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GAQ Qian, GUO Xueliang, HE Hui, LIU Xiange, HUANG Mengyu, MA Xincheng
2020,44(5):899-912, DOI: 10.3878/j.issn.1006-9895.1908.19114
Abstract:To characterize the microphysical characteristics and transformation process of stratiform clouds with embedded convections, a study was performed using the WRFV3 model and based on two aircraft measurements taken on May 1, 2009. The aircraft observation results showed that significant differences in the shapes and formation process of ice particles existed between the regions of stratiform cloud and embedded convection. Compared with the embedded convection region, the stratiform cloud featured more complicated shapes of ice crystals, including needle column, capped column, and dendrite types. However, the dendrite-type ice crystals dominated in the embedded convection region, and their growth was controlled by aggregation and riming processes. Overall, the results indicated that the basic characteristics of this stratiform cloud with embedded convections simulated by the WRF model agreed well with the aircraft observations, including cloud distribution, LWC, and numerical concentration on the flight route. The simulation results showed that in the stratiform cloud, with higher cloud water content and larger W, embedded convection could be developed because of a strong riming process. The hydrometeors of snow, graupel, and rainwater in the clouds accounted for 51.9%, 31.0%, and 16.0%, respectively, while cloud ice and cloud water accounted for very little. In the higher level, snow and graupel grew through deposition process. In the lower level, they grew through the riming process and melted into rain. Stratiform clouds with lower cloud water content and smaller W would remain as stratiform cloud. The hydrometeors of snow, rainwater, and cloud ice accounted for 90.4%, 6.1%, and 3.5%, respectively. The ice and snow grew through deposition process and melted into rain in the lower level.
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ZHAO Junhu, XIONG Kaiguo, CHEN Lijuan
2020,44(5):913-934, DOI: 10.3878/j.issn.1006-9895.1911.19132
Abstract:The real-time forecast accuracies of summer precipitation in Northeast China (NEC) from 1978 to 2018 were significantly low. Moreover, in the recent four years, when the prediction of the overall distribution of summer precipitation anomaly for the whole country was relatively accurate, the prediction of summer precipitation anomaly in NEC was contrary to the actual situation. Therefore, analyzing the cause for the low forecasting accuracy is necessary. In this paper, the forecasting ability of dynamic models and cognitive defects on forecasting summer rainfall in NEC are discussed. Moreover, by systematically reviewing the climatic characteristics, influencing factors, prediction methods of summer drought and flood in NEC, and the real-time forecasting skills, the causes have been obtained as follows: (1) The precipitation in early summer in NEC is mainly affected by the cold vortex activity in NEC, and in midsummer, it is mainly affected by the subtropical high in the West Pacific, the southerly wind in the Northeast, and the circulation pattern in the middle and high latitudes. However, the main dynamic climate models commonly used at home and abroad cannot accurately reflect the key circulation systems associated with precipitation in early summer and midsummer in NEC. (2) The relationship between the summer rainfall in NEC and the global sea surface temperature (SST) is weak and unstable. Especially, the influence of El Niño-Southern Oscillation (ENSO) on summer precipitation in NEC is complicated; the relationship between them varies from decade to decade. (3) The summer rainfall in NEC has remarkable multi-timescale variability (inter-seasonal, inter-annual, and inter-decadal timescales), influenced by different circulation systems, which makes accurately predicting summer precipitation in NEC more difficult. Finally, some scientific problems and possible solutions regarding summer rainfall forecasting in NEC are further discussed, which may be helpful for the future summer rainfall predictions in this area.
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2020,44(5):935-959, DOI: 10.3878/j.issn.1006-9895.2004.19135
Abstract:To study the effects of different boundary layer schemes on the simulation of landing attenuation stage of typhoon Meranti (1614), a series of high-resolution (1.33 km) numerical tests were carried out using seven boundary layer parameterization schemes in the mesoscale numerical model WRF v3.8, namely, YSU, MYJ, QNSE, ACM2, UW, GBM, and Boulac, in terms of movement track, intensity, structure, rainfall, and near-surface physical variables. The results indicate the following. First, boundary layer schemes significantly influenced the simulation of typhoon Meranti’s track, intensity, and rainfall during its landing attenuation stage, and the maximum differences in the 24-h simulated typhoon track, lowest atmospheric pressure, maximum wind velocity, and 24-h cumulative rainfall extremum were 80 km, 11 hPa, 27 m s-1, and 241 mm, respectively. Second, simulation results of the Boulac scheme showed a typhoon track that is closest to real-time results, followed by GBM, YSU, and MYJ schemes, and then by ACM2 and UW schemes, whereas the QNSE scheme displayed the worst simulation. Meanwhile, the UW and QNSE schemes simulated the lowest atmospheric pressure values, and MYJ and QNSE schemes simulated the maximum wind velocity values that are closest to actual observations. All boundary layer schemes simulated the features of the typhoon. For example, the lowest atmospheric pressure increased gradually during the landing stage, and the rate of such increase after landing was greater than that before landing, which agreed with real-time results. However, the increasing rate of the lowest atmospheric pressure before the typhoon landing that was simulated by each scheme is greater than the real-time result, whereas such increasing rate after typhoon landing is less than the real-time result. Third, the Boulac scheme best simulated the 24-h precipitation distribution, heavy precipitation area, structure, intensity, and TS score of precipitation at each level, whereas the MYJ scheme was the second best. As simulated by QNSE, UW, and ACM2 schemes, the rain belt advanced so quickly northwestward that the TS scores of precipitation at various levels were poor. Fourth, in the overall simulation of track, intensity, and precipitation of the typhoon, Boulac and MYJ schemes showed optimal results, in which the Boulac scheme was superior in simulating the typhoon track and precipitation and the MYJ scheme was superior in simulating typhoon intensity. The YSU and GBM schemes had the second best simulation results, whereas QNSE, UW, and ACM2 schemes had worse simulation performance. Moreover, the boundary layer schemes significantly differed in calculating the latent heat flux and sensible heat flux of near-surface layer, thereby affecting the simulation of typhoon track, intensity, and rainfall, leading to significantly different simulation results. The QNSE scheme resulted in an abnormally high latent heat flux, the MYJ and Boulac schemes resulted in the most modest values, and other schemes resulted in slightly smaller values. On the other hand, the QNSE scheme had a slightly higher sensible heat flux, the MYJ scheme showed the most modest one, and other schemes resulted in significantly smaller values. Finally, the boundary layer schemes significantly differed in the simulated thermal and dynamical structure of boundary layer, and Boulac scheme had the obvious advantages, particularly for the structure of boundary layer in daytime.
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PENG Jingbei, LIU Ge, SUN Shuqing, HE Kejun
2020,44(5):960-974, DOI: 10.3878/j.issn.1006-9895.1911.19141
Abstract:The East Asian winter monsoon (EAWM) has two dominant modes: the in-phase and out-of-phase variations of wind anomalies over northern and southern China. Different from the first mode reflecting a uniform strong/weak situation of the EAWM throughout eastern China, the second mode indicates a situation that the intensity of low-latitude EAWM over southern China is independent of and even opposite to that of mid–high-latitude EAWM over northern China. The present study focuses on the characteristics of tropical and subtropical circulation anomalies associated with the variability of low-latitude EAWM under the background of the second mode by using empirical orthogonal function analysis, correlation analysis, and partial correlation analysis. The results reveal that the inter-tropical convergence zone (ITCZ) can be considered as an important circulation system that contributes to the variation of low-latitude EAWM. Corresponding to a stronger and northward-extended ITCZ, convective ascensions over the tropical western Pacific and South China Sea are strengthened. This anomalous ascension may induce low-level anomalous northerly wind, thus resulting in a stronger low-latitude EAWM. In addition, the subtropical upper-level jet can be regarded as another important circulation system affecting the low-latitude EAWM. An increase in wind speed along the axis of the jet may cause anomalous northerly quasi-geostrophic winds near the jet entrance. Associated with the forced positive secondary circulation anomaly with anomalous descent (ascension) to the north (south) of the jet, the low-level anomalous northerly wind appears under the jet, which in turn, facilitates a stronger low-latitude EAWM. Finally, both the individual and joint effects of tropical convective activities and upper-level subtropical jet on the low-latitude EAWM are further investigated. Relatively, the influence of the ITCZ seems more important. When the two circulation anomalies simultaneously increase (i.e., more active convective activity of the ITCZ and stronger wind speed along the subtropical upper-level jet), their joint effect can significantly reinforce northerly winds to the south of 35°N over southern China and vice versa. The abovementioned results imply that the variability of low-latitude EAWM is not only affected by cold air surges from northern China but also modulated by the joint effects of tropical and subtropical circulation anomalies.
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2020,44(5):975-983, DOI: 10.3878/j.issn.1006-9895.1906.19145
Abstract:In the case of non-uniformly distributed layers, the vertical difference scheme used in GRAPES (Global/Regional Assimilation and Prediction System) model can only achieve first-order accuracy. A second-order scheme was designed and introduced into the GRAPES model in order to be used in the process of vertical discretization. An ideal test using the 1-D profile showed that the new scheme can improve the accuracy of difference computation obviously. An ideal density flow test was conducted to verify the correctness and stability of the new scheme in GRAPES model. A statistical evaluation of a medium-range forecast using the second-order scheme showed an improvement of forecast skill in large-scale fields, especially for the forecast after 120 h. Additionally, the second-order scheme was tested with a real-case experiment based on the extreme rainfall at South China, which again showed an improvement in the forecast of precipitation after 48 h.
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CHEN Yuxiao, XU Zhizhen, CHEN Jing, LI Hongqi, CHEN Fajing
2020,44(5):984-996, DOI: 10.3878/j.issn.1006-9895.2001.19157
Abstract:Precipitation ensemble forecasting is characterized by great uncertainty, and the uncertainty of the parameters in the physical that is closely related to the precipitation forecast is one of the sources of its numerical prediction error. As a frontier research field in international ensemble forecasting, the stochastically perturbed parameterization (SPP) method has been developed to address the uncertainty of representative model precipitation forecasts. To determine whether this method can reflect the uncertainty of numerical predictions of winter precipitation in China and provide a scientific basis for business applications, we used the China Meteorological Administration’s Global/Regional Assimilation and Prediction System (GRAPES) mesoscale regional ensemble prediction model and selected 16 key parameters from four parameterization schemes. These parameters, e.g., cumulus convection, cloud microphysics, boundary layer, and near-surface layer, greatly influence the uncertainty of model precipitation forecasts. In this paper, we introduce the stochastically perturbed parameterization (SPP) method and describe the results of an ensemble prediction experiment conducted from December 12, 2018 to January 12, 2019, a total of 31 days. We compare and analyze the effect of the SPP method on the winter weather situation and precipitation ensemble prediction. The results show that with the addition of a test for the SPP method, the results of probability prediction techniques for precipitation and isobaric elements are better than the control predictions without the SPP method, and the improvement of low-level and near-surface elements is better that of the iso-surface elements in the middle or upper floors. The precipitation prediction results obtained superior scores to those of the control prediction test, but because the improvement did not pass the test of significance, the differences were not statistically significant. The above results indicate that under the influence of the East Asian winter monsoon, the SPP method demonstrates no obvious improvement on the current prediction technique used for winter precipitation in China. The reason for this may be that the SPP method mainly represents the uncertainty of convective precipitation forecasting, whereas the winter precipitation process in China is mainly one characterized by the development of baroclinic instability. Because model precipitation is dominated by large-scale grid precipitation, and less convective precipitation, improvement in the winter precipitation forecast is not obvious. Thus, there is a scientific basis for applying the SPP method to the operation ensemble forecasting model.
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ZHONG Lihua, YANG Jing, LU Gaopeng, WANG Yongping, HE Qijia, QIE Xiushu
2020,44(5):997-1012, DOI: 10.3878/j.issn.1006-9895.2002.19169
Abstract:Red sprites are large-scale transient luminous events (TLEs) that usually occur between about 40 and 90 km altitudes above thunderstorms, and they are caused by cloud-to-ground (CG) lightning strokes and subsequent continuous current. Compared with studies that focus on sprites that occur in summer, those focusing on winter sprites are fewer due to limited comprehensive synchronous observation data. Influenced by the upper trough and warm, moist airflow at low level, a thunderstorm occurred in Arkansas, North America, on December 27–28, 2008. The Imager for Sprites and Upper Atmospheric Lightning (ISUAL) aboard the FORMOSAT-2 satellite could record two red sprite events. Using the red sprites optical observation data obtained by ISUAL, Doppler weather radar data, National Lightning Location data, ultra-low frequency magnetic field data, and cloud-top brightness temperature data provided by the National Environmental Center/Climate Prediction Center of the United States and the sounding data, this paper presents a detailed study of the characteristics of the winter thunderstorm that produced the red sprites and the related lightning activity. The results show that ISUAL did not record the halo that accompanied the two red sprites. The first was a columnar sprite, and the specific morphology of the second could not be determined because of its dim light. The parent thunderstorm of the red sprites was a mesoscale convective system (MCS), which appeared around 1500 UTC on the 27th near northern Arkansas and moved from west to east. The thunderstorm became stronger at about 2359 UTC, and the area of maximum radar reflectivity (55–60 dBZ) reached 339 km2 and then began to weaken. At 0303 UTC, the thunderstorm intensity increased, then the cloud gradually spread, and the thunderstorm began to weaken and completely dissipated at 1100 UTC. The first recorded sprite occurred at 0446:05 UTC, and the second at 0447:17 UTC. They tended to be produced in the dissipation stage of the MCS, when the frequency of the positive and negative CG lightning was low and the Percentage Of Positive CG to total CG (POP) increased significantly, and they were mostly over the stratiform cloud area with a brightness temperature of -40℃–-50℃. The sprite production was accompanied by an increase in the echo area of 30–35 dBZ. The area of radar reflectivity larger than 40 dBZ decreased, and the area of 10–40 dBZ increased during the sprite time window, suggesting that the sprite production was the decay of the thunderstorm and that the area of the stratiform region developed, which is consistent with the results of previous studies on summer sprites. The parent CG flash of red sprites was positive and with a single return stroke, and it was located in the trailing stratiform region of the MCS, where the radar reflectivity ranged from 25 to 35 dBZ. The corresponding radar echo top heights were 2.5 km and 5 km, and the peak currents were +183 kA and +45 kA, respectively. Based on the ultra-low frequency magnetic field data, the impulse charge moment changes (iCMCs) of two parent lightning discharges were estimated to be +394 C km and +117 C km. The ultra-low frequency magnetic antenna recorded the internal current signal of the first red sprite, indicating that the red sprite was strongly discharged.
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YANG Bingyun, LIU Jian, JIA Xu
2020,44(5):1013-1022, DOI: 10.3878/j.issn.1006-9895.1911.19181
Abstract:Cirrus clouds play an important role in atmospheric radiation and affect weather systems and climate change. Satellite remote sensing has considerable advantage in cirrus cloud detection, relative to traditional observation. As a passive remote sensing instrument, large deviations in the thin cirrus cloud top height data from the Moderate Resolution Imaging Spectroradiometer (MODIS) are detected. Comparatively, the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), which is an active remote sensing instrument, can acquire more accurate characteristics of thin cirrus cloud. In this study, MODIS cloud products in the Beijing–Tianjin–Hebei region from 2013 to 2017 are selected. Using the CALIPSO cirrus cloud top height data, a linear fitting method based on the cross-validation method is obtained, and the MODIS cirrus cloud top height data are corrected. The difference between MODIS and CALIPSO changes from -3 to 2 km to -2.0 to 2.5 km. Moreover, the maximum difference changes from approximately -0.8 km to approximately 0.2 km. In the context of different vertical levels and cloud optical depths, MODIS cirrus cloud top height data are improved after correction, which is more obvious at the lower cloud top height and optically thinner cirrus clouds.
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ZHANG Dianguo, WANG Shuo, GUO Xueliang, WANG Hong, FAN Mingyue
2020,44(5):1023-1038, DOI: 10.3878/j.issn.1006-9895.2004.19185
Abstract:On the basis of airborne Ka-band precipitation cloud radar (KPR) and droplet measurement technologies (DMT), the dynamic and microphysical characteristics of convective generating cells (GCs) embedded in stratiform clouds initiated by the Huanghuai cyclone on April 22, 2018 were analyzed. First, a total of 36 GCs were observed by KPR in spring in Shandong Province. The results based on the echo intensity, horizontal scale, and echo top height of these GCs show that the average echo intensity of GCs is concentrated at 20 to 30 dBZ, accounting for 69%. The horizontal scale of GCs is concentrated at 15 to 30 km, accounting for 61%. The echo top height of GCs is concentrated at 6 to 8 km, which is 2 to 4 km higher than the surrounding stratiform clouds. Afterward, the microphysical parameters of GCs in mixed-phase cumulus clouds on April 22, 2018 were counted. The results showed that the inner part of GCs is dominated by updraft with the maximum wind speed of 1.35 m s-1 and average updraft of 0.22 m s-1. GCs have high supercooled water content with the maximum of 0.34 g m-3 and average of 0.15 g m-3. The ice particle concentration in the inner part of GCs is 5.5 times that of its outer part, and the mean diameter of the inner part of GCs is 1.7 times that of its outer part. The images sampled by the cloud image probe showed that the ice particles on the head and tail of GCs were mainly columnar and radial, respectively, whereas the ice particles in the core of GCs were polymers. The growth of ice crystals depended on the accretion and collision processes. The ice crystals formed columns when the supercooled water was insufficient; otherwise, they rapidly formed graupels. The microphysical formation mechanism of precipitation in GCs is different and strongly depends on the supercooled water content. When the supercooled water content of the cloud was sufficient, graupels were rapidly formed, and surface precipitation was formed after they passed through the melting layer. When the supercooled water content of the cloud was insufficient, the formation of precipitation depended on the water vapor deposition and aggregation processes.
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2020,44(5):1039-1056, DOI: 10.3878/j.issn.1006-9895.2003.19186
Abstract:Atmospheric predictability research is the basis for weather and climate prediction. Under the background of global warming, meso/micro-scale extreme weather events such as heavy rain and severe convection have occurred more frequently in recent years, and their predictability has attracted wide attention. After briefly reviewing the history of atmospheric predictability research, this paper systematically reviews the latest advances in the predictability of heavy rain and strong convection over the last 20 years (1999–2018). The main research methods for meso/micro-scale predictability and their differences with traditional large-scale weather predictability methods are first discussed. Then, the primary initial error growth mechanism (error upscaling under deep moist convection) is elaborated in detail, and some arguments (error downscaling, error upscaling, and downscaling coexisting) are discussed. The effects of errors in NWP (Numerical Weather Prediction) models and convective environments on the practical predictability are also highlighted, and some recent mesoscale predictability experiments are reviewed. Finally, this paper briefly discusses the current problems, challenges, and future directions of the predictability research of heavy rain and severe convection.
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SHI Shiwei, ZHI Hai, LIN Pengfei, CHEN Tao
2020,44(5):1057-1075, DOI: 10.3878/j.issn.1006-9895.1912.19172
Abstract:Ocean salinity variation provides a new insight into related ENSO (El Niño–Southern Oscillation) expressed by climate variability. In this study, salinity variations and their related dynamic processes responsible for SSTA (sea surface temperature anomaly) were extensively compared and analyzed considering two strong El Niño events, 1997/1998 and 2015/2016, and one special El Niño, 2014/2015. The study shows that the development of ENSO is significantly associated with the occurrence and eastward diffusion of large-scale SSSA (sea surface salinity anomaly) in the western tropical Pacific. In April 1997 and 2015, corresponding to two strong El Niño events, there was a significant negative SSSA in the western–central Pacific. The anomaly moved eastward to the west of the dateline, which induced a shallower MLD (mixing layer depth), and a thicker BLT (barrier layer thickness), which enhanced the surface warming in the tropical central Pacific and the early warming in the equatorial eastern–central Pacific. Although a negative SSSA occurred in the April 2014/2015 weak event in the equatorial western–central Pacific, it did not develop eastward, resulting in a weakened thickening process of the BLT and a weak modulation effect on surface temperature. For the salinity change process corresponding to three El Niño events, surface advection and surface forcing caused by FWF (freshwater flux) were the major contributors to the salinity budget. Surface advection influenced the former variability of salinity tendency, inducing the occurrence of an ENSO signal. The precipitation in the tropical western Pacific had the most significant negative influence on FWF, which played a decisive role in the SSSA occurrence and ENSO development. Compared with the two strong El Niño events, the early FWF negative anomaly in 2014/2015 did not develop, did not move eastward, and weakened rapidly; this resulted in the slowing down of the negative salinity tendency in the western–central Pacific, deepening of the MLD, thinning of the BLT, and rapid cooling of the surface layer, which inhibited early warming in the equatorial eastern Pacific. The results of this study demonstrate that the salinity change was closely related to ENSO, and early SSS in the tropical western–central Pacific could be used as an index of SSTA. In particular, SSSA not only affects the strength of SSTA in oceans, it can also be used as a precursor to judge the development and strength of ENSO.
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ZHUANG Zhaorong, LI Xingliang, CHEN Jing, SUN Jian
2020,44(5):1076-1092, DOI: 10.3878/j.issn.1006-9895.1911.19193
Abstract:To improve the analysis quality by incorporating the flow-dependent ensemble covariance into the variational data assimilation system, the new GRAPES (global/regional assimilation and prediction system) hybrid-3Dvar system was built. The new system is based on the GRAPES regional 3DVar system, which uses the statistic covariance, and was built by augmenting the state vectors with another set of control variables preconditioned upon the ensemble dynamic covariance. The new hybrid-3DVar system and the localization method were verified through a single-observation assimilation experiment with ensemble samples produced by the 3D-Var’s control variable perturbation method. The real observation assimilation and forecast experiment for Typhoon Soudelor yielded the following conclusions: (1) The background covariance, which is represented by ensemble samples, is flow-dependent, and the root mean square spread in the ensemble of momentum field and mass field is largest near the typhoon center. (2) The analysis increments of the new hybrid-3DVar have a more detailed structure and more medium- and small-scale information. (3) The analysis and 24 h prediction qualities of model variables in the new hybrid-3DVar are significantly improved compared with the 3DVar system, and the precipitation position predictions are more accurate. (4) The 24 h forecast track of Typhoon Soudelor is closer to the observational one, and the 48 h-predicted intensity also approaches the real observation.
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ZHANG Lei, REN Guoyu, MIAO Shiguang, ZHANG Aiying, MENG Fanchao, ZHU Shichao, REN Yuyu, Suonan Kanzhuo
2020,44(5):1093-1108, DOI: 10.3878/j.issn.1006-9895.2004.19229
Abstract:Urbanization has a significant influence on the frequency and intensity of heat waves, but the mechanism of the effect of urbanization on the high-temperature process is not fully understood. In this study, the authors used the Weather Research and Forecasting (WRF) model to simulate a summer high-temperature process on 2–6 July 2010 in Beijing. This paper reports the main results obtained regarding the urbanization effect on the surface air temperature of urban areas during the heat-wave process. The optimized WRF model was able to simulate the temporal characteristics of the five consecutive days of high temperature and the variation in the urban-heat-island intensity (IUHI) in Beijing. The impermeability of the underlying urban surface lowers the 2-m relative humidity of urban areas with respect to that of rural areas, which weakens the ability of urban areas to regulate the surface air temperature via latent heat. After sunset, the urban-sensible-heat flux decreases slowly, and the cooling rate in urban areas is slower than that in rural areas. At night, the structure of the boundary layer is stable, and its height is low, as is the wind speed. In this case, the energy transmitted between urban and rural areas is constrained, and the strong urban heat island is formed, resulting in the temperature in urban area is significantly higher than that in rural area at night. After sunrise, both the sensible and latent heat fluxes of urban and rural land surfaces increase rapidly, and the stability of the boundary layer decreases. In the afternoon, the underlying urban surface favors high and low value centers in the sensible and latent heat fluxes, respectively, with a weakened ability to regulate temperature via latent heat. This is conducive to vertical exchange of energy, which decreases the stability of the boundary layer. The IUHI is lower in the afternoon than in the evening. Therefore, the obvious urban-heat-island effect created by the underlying urban surface in Beijing increases the strength of extreme-high-temperature events. Furthermore, in this heat-wave process, most of the eastern part of China is controlled by continental warm high pressure with clear skies and few clouds, and the northwesterly winds flowing over the Taihang Mountains generate a Fohn effect, which is the synoptic situations of the heat-wave formation in Beijing.
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ZI Ran, KONG Zhen, ZHANG Qiyue, XIA Yang
2020,44(5):1109-1124, DOI: 10.3878/j.issn.1006-9895.2005.19232
Abstract:Based on CMAP (Climate Prediction Center (CPC) Merged Analysis of Precipitation) monthly mean rainfall data and NCEP/DOE (National Centers for Environmental Prediction/Design of Experiments) II Reanalysis data from NOAA (National Oceanic and Atmospheric Administration) and the monthly precipitation and average temperature data from NMIC (National Meteorological Information Center), the authors defined an index (IAja) that describes the zonal asymmetric variation of the Asian westerly jet in the upper troposphere, from which the authors investigated the characteristics of the intensity difference between the eastern and western parts of the Asian westerly jet and its impacts on the climate of East Asia from 1979 to 2019. The conclusions are as follows: There are prominent interannual variations in the zonal asymmetry of the Asian summer westerly jet, with significant quasi-periods of 6–8 years and 2 years. When the zonal asymmetry of the Asian summer westerly jet is typically strong (weak), the wave-like anomalous rainfall pattern generates positive (negative)—negative (positive)—positive (negative) signs in the lower to higher latitudes in the East Asia sector along with negative (positive) temperature anomalies in the Lake Baikal area, and simultaneously significant positive (negative) anomalies in regions in West China and North Japan. The divergent and convergent wind components by the anomalous diabatic heating as a potential vorticity source directly induce the circulation anomalies in the mid-latitudes. The anomalous anticyclonic circulation causes the intensity of the west Asian jet to increase and the eastern segment to decrease, which strengthens the zonal asymmetry of the Asian summer westerly jet. The formation of and support provided by the zonal asymmetric anomalies of the Asian jet are affected by their convergence and divergence in the tropics and mid-latitudes, as well as the eastward propagation of wave energy in the westerlies. This eastward propagation of wave energy may be related to the sea surface temperature anomaly of the Northern Atlantic. These results facilitate a better understanding of the formation mechanisms of the zonal asymmetry of the Asian summer westerly jet.
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Suolang Tajie, SHI Ning, WANG Yicheng, ZHANG Dongdong
2020,44(5):1125-1140, DOI: 10.3878/j.issn.1006-9895.2003.19242
Abstract:Although the long-term trend of extreme temperatures has been extensively explored in previous studies, few studies have addressed the interdecadal variation of extreme temperatures. Based on the daily maximum temperature, minimum temperature, and daily temperature at 839 stations in China from 1961 to 2016, the authors analyzed the interdecadal variations in the winter extreme-low-temperature index in China. The first four wave components of the extreme temperature at each station were extracted by harmonic decomposition, which is regarded as the interdecadal component. A station is regarded as having undergone an obvious interdecadal variation if the cumulative variance explained by the interdecadal component is greater than 25%. The results show that the stations with obvious interdecadal variation in their winter extreme-low-temperature index are mainly located north of the Yangtze River, in northern Xinjiang, and in eastern Qinghai–Tibet Plateau. The interdecadal variations north of the Yangtze River and in northern Xinjiang are basically consistent after 1979. The years after 1979 can be divided into three periods: previously cold period (1979–1986), warm period (1987–2007), and later-cold period (2008–2016). The interdecadal variation in the extreme temperature indices of the stations located in the abovementioned two areas might be modulated by the interdecadal variation in the East Atlantic/West Russia (EAWR) teleconnection pattern, which corresponds to the interdecadal variation in both the frequency of the blocking-like circulation over the Ural Mountains and the amplitude of the planetary trough over East Asia.
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ZHOU Ying, ZHANG He, ZHANG Kewei
2020,44(5):1141-1154, DOI: 10.3878/j.issn.1006-9895.2002.19252
Abstract:As the atmospheric component of CAS-ESM1 (Chinese Academy of Sciences Earth System Model, version 1), IAP-AGCM4.1 (Institute of Atmospheric Physics Atmospheric General Circulation Model, version 4.1) is being developed independently by Institute of Atmospheric Physics. In this study, the authors used TECA (Toolkit for Extreme Climate Analysis) to identify and evaluate tropical cyclones (TC) over the western North Pacific simulated by IAP AGCM4.1 from 1979 to 2012. The results show that IAP AGCM4.1 can reproduce the spatial distribution, track, and source of TC reasonably well compared to observation data, but it underestimates the number of TC, with only 36% of the observed tropical cyclones over the western North Pacific simulated. Further analysis using K-means clustering revealed that this underestimation is mostly due to the model’s inability to reproduce northwestward-turning and westward TC. For TC with westward–northwestward, westward-turning, and eastward-turning tracks, the numbers simulated are approximately 39%, 48%, and 85% of those observed, respectively. Moreover, the correlation coefficients of the seasonal variations between simulated and observed TC can reach 0.91, with duration biases of roughly 1–2 d. IAP AGCM4.1 performs well in simulating the tracks of the westward–northwestward and eastward-turning TC, with relative biases ranging between 1%–5% for the longitude of the centroid, 4%–16% for the latitude of the centroid, and 5%–15% for the latitudinal and meridional standard deviations. In addition, IAP AGCM4.1 reproduces the evolutions of environmental circulation and subtropical highs quite well during the lifetime of eastward-turning TC, with the simulated strength and area indexes of the subtropical highs highly correlated with the observations (the correlation coefficient is 0.89). The poor simulations of northwestward-turning and westward TC are likely due to simulated biases in the subtropical high.
Volume 44,2020 Issue 5
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Dong Xinyu, Shi Xiaohui, Wen Min
Available online:April 19, 2024 DOI: 10.3878/j.issn.1006-9895.2404.23124
Abstract:The seasonal transition of the convective (STC) in the Maritime Continent (MC) during the boreal spring can largely influence the establishment of the Asian summer monsoon, but the interannual variability of STC in MC and its causes are still not well understood. In this paper, based on the climatic characteristics of STC in MC, we define some characteristic indicators of convection and circulation, further analyze the interannual variation characteristics of STC in MC, and explore the possible effects of sea surface temperature anomalies (SSTA) in the tropics and their mechanisms. The results show that the interannual variabilities of STC in MC and the evolution of atmospheric circulation over the surrounding areas have an overall consistency, and are mainly regulated by the El Ni?o ? South Oscillation (ENSO) events. In some special years, the distribution of the SSTA in the eastern tropical Indian ocean could stimulate an anomalous local atmospheric circulation, which will ultimately lead to some changes on the convective activity in MC.
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Available online:April 19, 2024 DOI: 10.3878/j.issn.1006-9895.2404.23129
Abstract:The summer precipitation in China is mainly affected by the East Asian summer monsoon, and the main factor affecting the monsoon is the land-sea thermal contrast. Based on the ECMWF / ERA5 reanalysis data and CN05.1 gridded precipitation data set from 1979 to 2022, this paper defines the European-Atlantic land-sea thermal contrast and two types of East Asian-Pacific land-sea thermal contrast: East Asia-North Pacific and East Asia-Subtropical High land-sea thermal contrast. The characteristics of three land-sea thermal contrast and the spatial and temporal characteristics of summer precipitation in China are studied, and the effects of land-sea thermal contrast on the mean and variability of summer precipitation in China and the influence of variability on extreme precipitation are analyzed. The results show that: (1) The precipitation in Northeast China, the lower reaches of the Yangtze River and the Tibet Plateau is significantly affected by the land-sea thermal contrast. The mean and variability of summer precipitation in these areas are increasing, and the increase of variability increases the probability of extreme precipitation in these areas. (2) The land-sea thermal contrast between East Asia-Pacific and Europe-Atlantic has maintained an increasing trend over the past 40 years and has shown an increasing trend under the medium emission scenario, and the land surface warming is higher than that of the ocean. (3) The main contribution of precipitation generation and change in Northeast China is the land-sea thermal contrast between East Asia-Pacific and East Asia-Subtropical High. The main contribution to the precipitation in the lower reaches of the Yangtze River is the land-sea thermal contrast between East Asia and the Pacific. The main impact on precipitation in the plateau area is the thermal contrast between East Asia-subtropical high and Europe-Atlantic sea and land. Finally, the results of LBM simulation further confirm that the Euro-Atlantic thermal contrast increases the precipitation in the western plateau and decreases the precipitation in the eastern plateau. These findings provide an important basis for us to understand the temporal and spatial variation of summer precipitation in China and the physical mechanism behind it.
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Li Yan, Xie Zuowei, Ding Min, Bueh Cholaw, 王月
Available online:April 17, 2024 DOI: 10.3878/j.issn.1006-9895.2404.23141
Abstract:This paper used the ERA5 reanalysis data to investigate the atmospheric circulation configurations and their evolution processes for three types of extreme low temperature events in the arid and semi-arid regions of China (dryland for brevity) during the winter half-year. This study examined the activity characteristics of transient eddies under different circulation configurations and their feedback forcing to the abnormal circulation. The results showed that the continuous amplification of tilted ridge and trough over the Eurasian continent was the key reason for extreme low temperature events in the dryland. This pair of ridge and trough was primarily maintained by the incoming low-frequency Rossby wave energy. Under its influence, transient eddies were abnormally active on the southern and northern sides of the titled ridge and trough, in which transient eddies in the south of trough guided part of cold air masses southward and further intensified the extreme low temperature events. In addition, the convergence and divergence of transient vorticity fluxes favored the continuous maintenance of tilt ridge and trough, which was conducive to amplification and eastward expansion of the low-level Siberian cold high pressure, and thus led to extreme low temperatures affecting the entire dryland. When the tilted ridge and trough were elongated longitudinally, the ridge over the Ural Mountain weakened and moved eastward as Rossby wave energy emitting downward. Correspondingly, the low-level Siberian cold high pressure also exhibited an eastward displacement, and the activity of transient waves was suppressed. The extreme low temperatures are mainly confined to the eastern dryland.
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Available online:April 15, 2024 DOI: 10.3878/j.issn.1006-9895.2401.23072
Abstract:Significant uncertainties exist in the ability of numerical models to reproduce heavy rainfall events over warm sector during the pre-summer rainy season in southern China. One such event occurred with heavy rainfall along the coastal line of Guangdong Province during the period of 29–30 May 2020, and all operational numerical models failed to predict this event at that time. Consequently, eight experiments were conducted to assess the influence of nudging surface-intensive observations into the numerical simulations. The findings reveal that nudging all surface meteorological elements, in what is termed the control experiment (EXP1), reproduces well the development of linear convection and the spatial and temporal evolution of heavy precipitation along the coastline of Guangdong Province. Sensitivity experiments focusing on nudging different surface elements indicate that nudging surface water vapor plays a pivotal role in convection initiation, primarily attributed to the swift escalation of relative humidity from 80% to near saturation (99%) within 3 hours in the low levels, accompanied by a marked reduction in convective inhibition (CIN), lifting condensation level (LCL), and level of free convection (LFC). Nudging surface temperature accentuates thermal buoyancy by amplifying potential temperature perturbations, thereby influencing the initiation and organization of convection. The occurrence and development of convection are considerably delayed in the absence of the nudging surface temperature, and its organization is less structured. Nudging surface wind helps to correct the near-surface southwesterly wind direction, aligning the convection evolution and the rainfall more closely with the observations. Additional six sensitivity experiments were carried out to further explore the impact of nudging duration on simulations. The results suggest that nudging all surface meteorological elements for 6 hours mirrors the outcomes of the control run, effectively reproducing well the heavy rainfall along the coastline. Despite a swift rise in water vapor within the initial 3 hours, the maintenance of water vapor for a certain time (another 3 hours) promotes rapid convection development. Thus, the numerical prediction performance of heavy rainfall in the warm sector over southern China can be improved to a certain extent by nudging surface intensive observations using the surface-grid nudging technique during the initial several (6) hours of model integration.
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CHI Yanzhen, WU Weijie, ZHENG Weipeng
Available online:April 09, 2024 DOI: 10.3878/j.issn.1006-9895.2402.23044
Abstract:The widely use of automatic weather station has greatly improved the accuracy of meteorological monitoring, providing important support for forecasting and warning, meteorological services, climate analysis and scientific research. Based on the daily precipitation data of the national and automatic weather station in 2015-2021, the multi-scale spatial and temporal distribution of precipitation, the spatial category and intensity characteristics of heavy rainfall, and a brief weather background were analyzed. The main conclusions are as follows:(1) Based on the area-density weights of the rainstorm stations in each district, the spatial classification index of the heavy rainfall is developed with 4 categories of local, regional, wide-range and territory-coverage considering the independence of the assessment factors and the non-uniform distribution of the stations. Based on the area weight of the number of rainstorm stations and the disaster-causing effects of different magnitude rainfall, the assessment index of heavy rainfall intensity is developed. By using the percentile method to determine the intensity grade of heavy rainfall, the spatial range and intensity of heavy rainfall are closely connected.(2) The precipitation in Xiamen was characterized by significant regional heterogeneity and local characteristics due to the topographic and geomorphological characteristics of mountains, sea and bays. The mean annual precipitation and heavy rainfall frequency increased gradually from the coast to inland, and the frequency of rainstorm was closely related to the distribution of topography. (3) In 2015-2021, there were 106, 37, 16 and 5 rainstorms of the aforementioned category in Xiamen, accounting for 65%, 22%, 10% and 3%, respectively.Heavy rainfall occurred in every month, and concentrated in the main flood season from May to September, with peaking in June and August.There were 8 extremely heavy, 24 heavy, 33 relatively and 99 general cases, and the total intensity and average intensity ranked firstly in 2016 and the weakest in 2020. The spatial category of the 8 extremely heavy events was territory-wide scale, while the 99 general heavy rainfall were all local-range events.(4) The main influencing systems of the regional torrential rain processes included warm-cold air activities, tropical cyclones, southerly stream, northward uplift of convergence zone, low-level wind shear and strong convection, etc. The wide-range especially the territory-wide heavy rainfall caused mainly by warm-cold air activities and tropical cyclones. A rare territory-coverage winter heavy rainfall event occurred on 9thDec 2015 due to the impacting of weak cold air and the strong warm moist airflow.The results can be used as a scientific reference for monitoring, forecasting, assessment and service of heavy rainfall.
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DUAN YAWEN, YANG QING, MA ZHUGUO, ZHENG ZIYAN, LI MINGXING
Available online:April 09, 2024 DOI: 10.3878/j.issn.1006-9895.2304.23062
Abstract:The spatial distribution of summer rainfall anomalies over eastern China often characterized by meridionally banded structure. The possible change of it in response to global warming is of great significance to water resource management and disaster prevention. Previous studies show critical role of climate variability on modulating these rainfall modes while seldom studies considered model’s internal variability on investigating their responses to increased greenhouse gas. Based on model simulations with different forcings from the fifth Coupled Model Inter-comparison Project (CMIP5), this paper analyzes the response of the leading modes of eastern China summer rainfall to increased CO2 concentration with consideration of model internal variability. The results show that increased CO2 would not change the leading modes of eastern China summer rainfall. The tripole and dipole mode during the recent decades would still be the leading modes in the abrupt quadruple CO2 experiment (4×CO2) and 1% per year increased until quadrupled CO2 experiment (1%CO2) with the dipole mode plays a more dominant role. However, the frequency, intensity and trend of these modes will change. Compared to pre-industrial control simulation (piControl), the temporal variability of the tripole and dipople mode both decrease under 4×CO2 forcing. The variability of dipole mode intensifies while tripole mode weakens under 1%CO2 forcing. With the gradually accumulation of CO2, the occurrence of the positive and negative phase of these modes will change. The phase of tripole mode which featured with drought over the Yangtze River Basin while flood over North and South China would happen more frequently. So does the “Southern flood and northern drought” phase of the dipole mode. Compared to piControl simulation, the sea surface temperature and atmospheric circulation anomalies associated with the dipole and tripole mode both weaken under 4×CO2 forcing. Whereas under 1%CO2 forcing, their differences are regional dependent. The tripole mode is associated with weakened anomalies over the Indian and western North Pacific Ocean while the dipole mode is associated with stronger central and eastern tropical Pacific and North Pacific sea surface temperature anomalies.
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shenshangqi, huangqijun, gexuyang
Available online:April 09, 2024 DOI: 10.3878/j.issn.1006-9895.2310.23073
Abstract:In this study, rapidly intensifying (RI) tropical cyclones (TCs) with ‘Atypical’ convection in the Northwest Pacific were screened by using reanalysis data and infrared cloud images. A group of slow-intensifying (noRI) typhoons with ‘Typical’ convection were gathered for comparison. It is found that the RI group has a stronger maximum region of surface latent heat flux on the left side of the vertical wind shear (VWS) direction. To further explore possible mechanisms, the ‘Atypical’ convection case ‘Lekima’ (2019) was selected for sensitivity numerical experiments. The diagnostic results indicate that the surface latent heat flux on the left side of the VWS direction helps establish convective-instability in the region. Consequently, the effect of the "Ventilation effect" was weaken through the "Boundary layer entropy recovery" mechanism caused by the surface latent heat flux. Under easterly VWS, convection activity can be enhanced in high surface latent heat flux regions during the transition from the down-shear to the up-shear, thereby stimulating strong upper outflow channels. The establishment of outflow channels (Outflow blocking mechanism) can resist the environmental easterly flow, which weakening the strength of VWS, and allowing the typhoon to develop vertically.
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Hu Qiyuan, QIN Zhangcai, QI Youcun, ZHU Ziwei, FENG Dian, ZHANG Li
Available online:April 09, 2024 DOI: 10.3878/j.issn.1006-9895.2403.23117
Abstract:The raindrop spectrum, as a high-frequency observation data that directly describes the characteristics of raindrop size and quantity, has been widely used in the fine evaluation and analysis of raindrop changes in different weather conditions and types. The study utilized raindrop spectrum observation data from 2019 to 2022 in the Shaanxi Province. We have analyzed the overall characteristics of precipitation under the influence of five weather circulations, the drop spectra characteristics of rainstorm and non-rainstorm processes, and the drop spectra characteristics of convective precipitation and stratiform precipitation. The results indicate that the contribution of precipitation with rainfall rate>5mm h-1 to the total rainfall of the process varies significantly among different circulation systems. The main reason for this situation is the difference in the number concentration and contribution of raindrops in each diameter intervals. For example, the southwest airflow type is often characterized by stable precipitation formed by long-term high concentration small raindrops, while the northwest airflow type is characterized by strong precipitation formed by short-term high concentration large raindrops. The characteristics difference of drop spectrum between different circulation rainstorm and non-rainstorm further increase, and heavy rainfall have a significant promoting effect on raindrop spectral parameters. From the variation of number concentration with diameter, the number proportion and diameter spectral width of convective precipitation raindrops with rainfall rate>5mm h-1 in the rainstorm are generally higher than those of non-rainstorm. The distribution range and magnitude of Dm-Nw between convective precipitation and stratiform precipitation are nearly similar, with differences in the location of mean and high value areas. Compared with similar regions such as Zhaosu, Zhuhai, and Palau Island, most of convective precipitation in Shaanxi tends to have oceanic convective precipitation characteristics. A few continental convective precipitation occur in flat straight airflow weather or northwest airflow weather. Based on the above analysis, this study differs from the traditional Z-R empirical relationship and optimizes the fitting of Z-R precipitation estimation equations for various circulation precipitation based on raindrop spectra, which helps to improve the accuracy of radar precipitation estimation in different weather scenarios in the local area in Shaanxi.
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GaoWenliang, YuShuhua, PengJun
Available online:April 07, 2024 DOI: 10.3878/j.issn.1006-9895.2309.23078
Abstract:Using the 1998-2018 NCEP/NCAR global analysis data, atmospheric observation data, and the Tibetan Plateau Vortex (TPV) and shear line yearbooks, a comparative analysis was conducted on the structural characteristics of high-impact eastward moving plateau vortices with quasi-straight long (QSLTPVs ) and short paths (QSSTPVs ) adopting synthetic method. The relationship between the intensity and structure of long and short path vortices was further discussed, thereby indicating that the evolution of long and short path vortices is to some extent determined by the structure of the low vortex itself. The results show that the long and short path vortices have the same structural characteristics, namely, the off-center vortex circulation vertical structure, the coincidence of the center of the low vortex and the positive vorticity center before its departure from the Tibetan Plateau, and the consistent trend of the vortex variation of the low vortex in different activity stages, and the upward motion mainly occurs in the south wind area east of the TPV vertical axis. The differences in the structural characteristics of long and short path vortices are clearly manifested during strengthening stage. The positive vorticity column and upward motion column associated with the long path vortex are stronger than those of the short path vortex. The positive vorticity column associated with the long path vortex tilts northward and has a symmetrical distribution compared to the short path vortex. The convective intensity of positive vorticity coming into the vortex area of the long path vortex is stronger than that of the short path vortex. The transfer of high-altitude westerly momentum of the long path vortex is more evident than that of the short path vortex. The center of south wind associated with the long path vortex is further to the east than that of the short path vortex. The intersection of east and west winds of the long path vortex is further to the south and stronger than that of the short path vortex. The positive vorticity advection center overlying the vortex area of the long path vortex is lower when it departure from the Tibetan Plateau and lasts longer, deviating to the east of the TPV, while the short path vortex is on the opposite side. These differences indicate that the long path vortex has a dynamic mechanism that is conducive to the long-term eastward movement of the TPV.
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Guo Ziyi, Huang Qian, Yao Suxiang
Available online:April 07, 2024 DOI: 10.3878/j.issn.1006-9895.2402.23126
Abstract:Atmospheric low frequency oscillations are closely related to summer precipitation and related catastrophic weather in China, and it is of great significance to study the effects of 10-30-day low frequency oscillations on weather and climate. In this paper, the effects and mechanisms of the 10-30-day oscillations at mid-high latitudes and low latitudes on the average summer precipitation in China during the period 1991-2020 are investigated by using station observations data and ERA5 reanalysis data, etc. According to the singular value decomposition(SVD) analysis, the 10-30-day oscillations at mid-high latitude are closely related to the spatial distribution of inverse-phase precipitation over Yangtze River and South China Sea, When the 10-30-day oscillations in north of Lake Baikal are weak and the oscillations in south of Lake Baikal are strong, the precipitation exhibits a significant decrease in the Yangtze River basin while showing a notable increase from the South China Sea to South China; The key region of the low latitudes 10-30-day oscillations is located in the northwestern Pacific, where precipitation in southern China exhibits a significant positive anomaly during periods of strong oscillation within this region. The 10-30-day oscillations at mid-high latitudes mainly affect the mean position of the summer subtropical westerly jet stream through wave-current interactions, which makes the position of the secondary circulation near the jet stream to be anomalous, thus indirectly affecting the precipitation in the Yangtze River Basin and the South China Sea to South China, and making it show anomalous inverse-phase distributions; Distinguishing it from the mid-high latitudes, the 10-30-day oscillations at low latitudes over northwest Pacific propagate northwestward to southern China, directly inducing precipitation anomalies.
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LI Yao, ZHANG Tiening, ZHAO Shuhui, SUN Li, ZHAI Qingfei
Available online:April 07, 2024 DOI: 10.3878/j.issn.1006-9895.2312.23095
Abstract:In order to study the vertical structure of precipitation in the northeast cold vortex cloud system further, this paper analyzes the microphysical characteristics of the three northeast cold vortex rainfall weather processes in Fumeng County since 2020 by using the micro-rain radar and laser raindrop spectrometer deployed in the national ground observation station of Fuxin Mongol Autonomous County, Liaoning Province. The results show:in the cases dominated by stable precipitation of Stratus clouds, the raindrop spectra measured by the micro rain radar and the raindrop spectrometer have a good consistency, while in the cases with more convective precipitation. The average raindrop spectrum observed by the micro rain radar and the raindrop spectrometer only shows good consistency in the medium particle segment (1-2.5mm); in the stratus precipitation stage, the smaller ice crystal particles begin to melt faster through the 0℃ layer, and the small cloud droplets accumulate below the 0℃ layer, and several concentrations of extreme values appear, below the extreme value, the larger ice crystal particles experience a longer melting distance and become larger raindrops, at the same time, the accumulation of small cloud drops further promotes the collection and collision effect of large cloud droplets, which is conducive to the formation of large raindrops, and a spectral width extreme value appears below the zero degree layer, which is manifested as a vertical raindrop spectrum "Bulge", "Bulge" occurs within 2-3 minutes from the onset to the fall. The "bulge" can be seen as the intuitive performance of the bright band promoting precipitation in the stratus precipitation stage, but whether this promotion of precipitation can bring a significant increase in rainfall intensity on the ground depends on the water vapor content in the near-ground atmosphere, which is manifested in western Liaoning, in dry spring, the relative humidity of the atmosphere is low, and the bright band does not help the broadening of the raindrop spectrum on the ground, but in the summer when the water vapor is relatively abundant, the downward movement of the "Bulge" to a certain extent leads to the widening of the near-ground raindrop spectrum and the increase of rain intensity; Compared with other regions, the precipitation concentration in western Liaoning is small, but the average concentration of stratus precipitation and convective precipitation is not much different, and the difference in mass-weighted diameter leads to the difference in rain intensity.
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Zhu Li, Jiang Xingwen, and Lu Ping
Available online:April 07, 2024 DOI: 10.3878/j.issn.1006-9895.2311.23074
Abstract:In this paper, using multi-source high-resolution data analyzes the triggering mechanism of convection in the second stage of the most vigorous development of convection during the heavy rain in Ya"an, Sichuan on August 4, 2021. The conclusions are as follows: (1) The mesoscale disturbance system in the middle and upper troposphere provides favorable dynamic and thermodynamic conditions for the triggering and development of convection in the second stage of the process. (2) The surface convergence line formed by the outflow of the cold pool can directly trigger convection, while the surface convergence line formed by the mountain-to-plain flows and the topographic circumfluence cannot directly trigger convection, Convection can be easily triggered only when there is a "secondary uplift mechanism" in the upper and middle layers of the boundary layer. The "secondary uplift mechanism" includes the coupling uplift mechanism of the ambient atmospheric convergence and uplift, the forced uplift of high altitude terrain, and the upstream updraft in front of the moving residual weak convection system. (3) The positive vorticity zone formed on the northeast side of Mount Emei under the mechanical forcing of terrain is conducive to the strengthening and development of convection. The low-level jet generated by the strong convective system moves northward and meets the cold pool outflow south of Mount Longmen, triggering the "elevated convection". This convection triggering mechanism is closely related to Mount Emei and nearby high-altitude mountains, and may be a unique convection triggering mechanism in the eastern slope of the Qinghai Tibet Plateau. (4) Under the action of different triggering mechanisms, the time difference and relative position of lift formation and convection initiation are different, among which the time difference and relative position distance are longer under the action of the mountain-to-plain flows and terrain flow.
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Wei Lei, Hong Liangyou, Yang Junfeng, Zhang Rong, Hu Wenhao, Hou Tuanjie, LV Yuhuan
Available online:April 07, 2024 DOI: 10.3878/j.issn.1006-9895.2312.23007
Abstract:Based on the wind field data from FNL reanalysis data, the atmospheric wind field of the height range of 0.8-47 km above Taiyuan (112.35oE, 37.37oN) is investigated. The vertical distribution characteristics and wind shear characteristics are analysed by the method of vector averaging and mathematical statistics. The wind field over Taiyuan is investigated for its effects on aircraft launch, leading to a classification of four periods based on wind characteristics: April, May and June are the early rainy season, July and August are the rainy season, September and October are the late rainy season, and November, December and January to March are the winter. According to the seasonal variation of the wind field, the vertical structure is divided into three layers with two height layers of 5 and 20 km. Below 20 km, the average wind speed in the rainy season is lower than in the other three periods. Above 20 km, the wind speeds in the winter and rainy season are higher than that in the early and late rainy season. The wind shear characteristics are calculated using the integrated vector wind method. The intensity of wind shear is greatest in the height range of 40-47 km in winter, and the maximum intensity value occurs around 12 km in other periods. The primary influence range of the wind shear caused by the maximum wind is within ±8 km. By using the new λ-PDF polynomial chaotic expansion method, the wind field parameters are effectively fitted and the uncertainty of the wind field distribution is resolved, providing theoretical support for complex flight problems.
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Available online:April 03, 2024 DOI: 10.3878/j.issn.1006-9895.2403.23106
Abstract:Based on the EAR5 daily reanalysis data and observational precipitation data at 2437 stations in China from 1979 to 2020, this study analyzes the zonal oscillation characteristics of the East Asian subtropical westerly jet and its relationship with the East Asian atmospheric circulation and precipitation during the Mei-yu period. The results reveal that there are two intensity and position variation types for the East Asian subtropical westerly jet during Mei-yu period by comparing the 200 hPa regional mean zonal wind anomalies in a large value area of standard deviation (37o-47oN, 100o-120oE) with the two jet stream centers over the Western Pacific (37o-47oN, 140o-160oE) and the Tibetan Plateau (37o-47oN, 80o-100oE). For the first type, the jet stream center is situated over the western Pacific Ocean in the early stage, then the intensity of the jet stream over the western Pacific weakens, and an enhanced jet stream center appears on the western side of the jet stream. The maximum zonal wind shows a rapid westward migration feature, which is called the rapid westward migration type. For the second type, the jet stream center is located over the Tibetan plateau in the early stage, then steadily strengthens and moves eastward. The maximum zonal wind exhibits a gradual eastward migration feature, which is referred to as the gradual eastward migration type. The analyses of circulation and precipitation corresponding to the two jet stream oscillation types indicate that, with the rapid westward migration of the jet stream, the east ridge point of the South Asian High is located to the east, and the western Pacific Subtropical High’s intensity is increased and moved to the west, and the circulation pattern in the middle and high latitudes is characterized as "two troughs and one ridge". Furthermore, as the meridional increase of 200 hPa divergence and the 700 hPa water vapor transport rises to the north, the position of the rain belt shifts from south to north. Corresponding to the gradual eastward migration type, the east ridge point of the South Asian High is located to the west, and the western Pacific Subtropical High’s intensity is decreased and contracted to the east, the circulation pattern in the middle and high latitudes is featured as "two ridges and one trough," and the blocking highs occur more frequently over the Okhotsk Sea region. Meanwhile, the upper-level divergence in the lower reaches of the Yangtze River weakens, while the upper-level divergence and lower-level water vapor transport strengthen in the upper reaches of the Yangtze River, thus forming an antiphase change in precipitation intensity between the upper and lower reaches of the Yangtze River.
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Available online:February 08, 2024 DOI: 10.3878/j.issn.1006-9895.2402.24014
Abstract:In 2023, National Natural Science Foundation of China (NSFC) received 114 applications for the Meteorological Joint Fund (MJF). After peering review, 48 applications were selected and entered the final competition where 28 applications were downselected and funded. The average funding rate is 24.8%. From the perspective of project applications, cooperation applications from different unit attributes account for 86%. There is a clear difference between MJF and the key programs in the field of “weather, climate, and associated sustainable development” of the Department of Earth Sciences (DES). The former has a technical research proportion of over 50%, while the latter has a proportion of less than 30%. 50% of the applicants are the scientists in the National High end Talent Program, indicating strong competition in applying for MJF. From the perspective of review and funding, the rating is better than previous years, with an average comprehensive score of 3.7 points from specific review projects, which is comparable to conventional key programs. Universities and the Chinese Academy of Sciences have been funded more than the organization within China Meteorological Administration, with 16 projects, accounting for 57% of the total funded projects. The average funding intensity of MJF is 2.627 million yuan per project, exceeding the funding intensity of 2.3 million yuan per project from the conventional key programs of DES, NSFC.
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Available online:January 19, 2024 DOI: 10.3878/j.issn.1006-9895.2310.22063
Abstract:Based on ERA-5 0.25°×0.25°reanalysis data, this paper calculated wet potential vorticity and frontier-generating function of the extreme rainstorm during 6 to 7 May, 2020 occurred on the north slope of the central Kunlun Mountains, the evolution characteristics of atmospheric instability in rainstorm process was analyzed, and the role of frontal system in convective triggering was clarified. The results showed: (1) During the heavy rainstorm period, the rainstorm area was controlled by the divergence superposition area caused by two stream jets at 200 hPa, the Central Asian vortex and the slowly-moving shear line in the north of the Plateau at 500 hPa. Additionally, the topographic convergence lifting at 700 hPa, and the confrontation of the cold air parcel in front of the surface high and the warm air parcel from Tarim basin, which provides favorable dynamic and thermal conditions for the development of the cloud cluster in the shallow mountain area on the northern slope of the Middle Kunlun Mountains. (2) The rainstorm process was divided into two stages. In the first stage(EP1), there was convective instability layer at the lower troposphere over Yutian to Qiemo area. In the second stage(EP2-1), there was a short-time heavy rainfall occurred in Cele station. The convective instability in the lower troposphere gradually translated to the symmetric instability, and the variation of Mpv2 at the lower troposphere was caused by the wet atmospheric baroclinic and vertical shear of the lower horizontal wind. Affected by the early short-time heavy rainfall and the release of latent heat of condensation, the lower layer atmosphere became warmer and moistened over Cele to Luopu area, and the lower layer atmospheric stratification stability turned into convective instability in the second stage(EP2-2). (3) The uplifting of terrain convergence and the frontogenesis at lower-upper troposphere in the northern plateau were the main reasons for the formation of mesoscale cloud clusters in the first stage. The cold front in the lower troposphere triggered the release of convective unstable energy, and the clouds near Qiemo developed rapidly. At the same time, the airflow which piled up in front of the hill climbed to the vicinity of 500hPa, the cold front frontogenesised and confronted the warm front on the north side of the plateau for a short time to form a cold occluded front. The vertical movement near the front enhanced the rapid development of convective clouds, and gradually merged with the convective clouds near Qiemo, resulting in the first stage precipitation (EP1) from Tian to Qiemo. During the second short-time heavy rainfall stage over Cele area(EP2-1), The cold front of 700 hPa in the lower troposphere frontogenesised, and the warm and wet inflow air in the direction of cloud movement met with the cold air mass of evaporation under the cloud and inflow behind the cloud. The warm air mass climbed further along the bottom cold pool, which made the cloud rapidly develop to mature stage, resulting in a short-time heavy rainfall over Cele area. As the Central Asian low vortex gradually entered the Northern Slope of the Middle Kunlun Mountains, the cold front frontogenesised in the lower troposphere and middle troposphere further strengthened the development of the upward movement, which was an important reason for the continuous precipitation from Cele to Luopu area in the second stage(EP2-2).
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lihaoqian, wanglu, chenlin, sunming, gezian, chengyifeng, zhangronghua
Available online:January 19, 2024 DOI: 10.3878/j.issn.1006-9895.2312.23111
Abstract:This study investigates the simulation skill of Meiyu precipitation over the middle and lower reaches of the Yangtze River (MLYR) in the regional climate model of RegCM4.7. To examine the potential roles of the cumulus convective parameterization schemes (CCPSs), horizontal resolutions (HRs), microphysics parameterizations and land models on the simulation skill of Meiyu precipitation, we carried out totally 96 sets of numerical experiments based on various model configurations. In general, RegCM4.7 has good performance in simulating the Meiyu precipitation over the MLYR, from the perspective of both the Meiyu simulation experiments for the super Meiyu case in summer 2020 and the long-term period of 1990-2020. Our quantitative analysis reveals that the CCPS plays a vital role in influencing the Meiyu simulation skill. Specifically, the Tiedtke scheme shows the best performance in yielding Meiyu precipitation, whereas the Grell scheme shows relatively low skill. The relatively reasonable simulation with the Tiedtke scheme was attributed to the reasonable representation of the convective precipitation, as well as the ratio of the convective precipitation to the stratiform precipitation. Furthermore, the impacts of HRs on the Meiyu precipitation simulation are tightly tied to the terrain. The low-HR (60 km) experiment tends to show a significant overestimation of precipitation over the complex terrain region. Along with the increase of HR, such wet bias of precipitation due to complex terrain can be significantly reduced. It is found that the mesoscale convective system (MCS) precipitation is anchored by steep terrain in the low-HR experiment, leading to the wet bias in long-term average of the precipitation; in contrast, the high-HR experiment is able to duplicate the diurnal variation of the MCS over the complex terrain that is generated in the afternoon and gradually propagates eastward, and such reasonable representation of MCS’s feature ultimately contributes to the reasonable long-term average of the precipitation during the Meiyu season. Besides, the results show that the Meiyu simulation skills are not sensitive to the choice of the microphysics parameterizations and land models. Overall, the current numerical experiments show that RegCM4.7 is capable of simulating Meiyu precipitation over the MLYR (even for the super Meiyu case in 2020), and the configuration with the Tiedtke CCPS tends to have the better simulation skills than other CCPSs in the RegCM4.7.
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WU ZIHAO, LIU ANKANG, WANG HONGLEI
Available online:January 16, 2024 DOI: 10.3878/j.issn.1006-9895.2309.23040
Abstract:To analyze the characteristics of cloud condensation nodules (CCN) and aerosol particle size distribution and their influencing factors in the Middle Tianshan region of Xinjiang, aerosol and CCN number concentration data were measured using an aerosol wide-range particle size spectrometer and a Cloud Condensation Nodule Counter from August 4–25, 2019, and combined with meteorological element data and the HYSPLIT model for comprehensive analysis. The results show that during the observation period, the mean value of aerosol number concentration in Tianshan was 3607±4105cm-3, with the highest percentage of Aegean nuclear mode particles (64.76%). The mean values of CCN number concentration at 0.1%, 0.2%, 0.4%, 0.6% and 0.8% supersaturation were 185±185cm-3, 648±345cm-3,1576±1045cm-3, 2077±1417cm-3 and 2408±1657cm-3, respectively. The average spectral distribution of aerosol number concentration showed a unimodal distribution with peak particle size located at 29.5 nm. The diurnal variation of aerosol number concentration peaked at 08:00 (Beijing Time, the same below), 17:00 and 20:00, which was mainly affected by the diurnal variation of boundary-layer height, mountain-valley wind, emission sources, and other factors. The aerosol particles in the Tianshan mountains during summer were found to exhibit different modes of distribution. The Aitken mode particles displayed a bimodal distribution, while the accumulation mode particles had a trimodal distribution. The number concentration of nuclear mode particles showed a unimodal diurnal variation, which may be attributed to new particle formation. The CCN activation spectrum fitting result is N=3111S0.896 (N is the CCN number concentration at the supersaturation S), which is a clean continental type feature. The diurnal variation of CCN number concentration peaked at 08:00, 18:00 and 21:00. New particle formation (NPF) is beneficial to the increase of CCN number concentration at the mountain Tianshan. Under the supersaturation of 0.1%, 0.2%, 0.4%, 0.6% and 0.8%, the average concentration of CCN in NPF day is 13%, 18%, 25%, 22% and 20% higher than that in the non-NPF day, respectively. The relative humidity (RH) has a greater impact on the concentration of nucleation mode particles and a smaller impact on the concentration of other mode particles. As RH increases, the aerosol size distribution shifts towards larger particle sizes. When RH>60%, the number concentration of aerosol and CCN decreased with increasing RH. The aerosol and CCN number concentrations are higher under northerly and easterly winds due to the influence of topography and valley winds. There are four main types of air masses in Tianshan: western (29.2%), northwestern (29.3%), northeastern (27.0%), and southern (14.5%). The aerosol number concentration of the northeastern air mass from the northern Tianshan Mountains is the highest at 5449±3793cm-3 and the lowest at 1971±2087cm-3 due to the different direction and movement path of the air masses and the influence of the northern urban zone. The northeastern air mass has higher CCN number concentrations at all supersaturation levels, which are 100%-150% higher than the lowest southern air mass.
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YISILAMU Wulayin, Miao JunFeng, WU BingXue
Available online:January 15, 2024 DOI: 10.3878/j.issn.1006-9895.2308.23028
Abstract:Sea Breeze Front（SBF）is the landward edge of the sea breeze circulation, which has similar characteristics to the cold front. SBF has always been a key object of coastal meteorological research since it can trigger strong convection even disastrous weather such as thunderstorms in coastal areas. In this paper, a typical SBF over the Hainan Island is investigated using the Weather Research and Forecasting model（WRF）. Sensitive experiments are designed to study the impact of land cover changes on the structure and evolution of SBF and its possible mechanism. The results show that impact of land cover change on SBF is determined by the comprehensive influence of multiple surface and vegetation attributes. The dynamic effects of the afforestation inhibit the development of SBF, while the thermal effects promote it, which means the influence of afforestation on SBF is the result of competition between the two opposite forces. The decreased albedo and increased leaf area index leads to a small increase in sensible heat fluxes, which can increase the temperature difference between land and sea which is the sea breeze driving force. The increase of surface roughness can decrease the wind speed, inland propagation and vertical velocity of SBF. However, the difference of SBF between FOREST and CNTL experiment is found to be small because of the large forest land use of the Hainan Island. In contrast, the thermal and dynamic effects of deforestation are both beneficial to promote the development of SBF. The increased albedo and decreased leaf area index results in a significant decrease in latent heat flux, and an increase in sensible heat flux at afternoon. Therefore, it is very obvious that warming and humidification effects of deforestation on the lower atmosphere, which increases the sea-land temperature gradient. On the other hand, the decrease of surface roughness leads to the increase of wind speed. Consequently, the wind speed, inland propagation and vertical velocity of SBF are significantly increased.
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Available online:January 15, 2024 DOI: 10.3878/j.issn.1006-9895.2305.22229
Abstract:Based on the causality of information flow, this study examined predictors for the dominant modes of autumn precipitation in Southwest China (SWC), then a statistical model of autumn precipitation in SWC was established. Finally, the prediction skills of the empirical model were evaluated. The first two dominant modes of autumn precipitation during 1979-2020 in SWC are basin mode and saddle mode obtained by empirical orthogonal function (EOF), which are closely related to the developing of eastern El Ni?o and central El Ni?o. The predictors of PCs of the first two dominant modes are chosen to begin with the causality of information flow. The multiple linear stepwise regression with leave-one-out method was applied to further select the predictors and then establish a statistical model. During the training period from 1980 to 2015, the correlation coefficients between predicted PC1 and PC2 and actual PCs are 0.89 and 0.83, and the sign coincidence rates are 90% and 83%, respectively. In the forecast years from 2016 to 2020, the predicted PC1 and PC2 are in phase with the actual PCs in four years, with the sign coincidence rate being 80%. During the 36-year training period from 1980 to 2015, the averaged anomalous pattern correlation coefficients (ACC) between the reconstructed precipitation with the predicted PCs and the observed precipitation anomalies is 0.48. ACC is greater than 0.5 in more than 1/2 years. The regional averaged temporal correlation coefficient (TCC) is 0.48. We also conducted similar-year forecast with predicted PC1 and PC2 to make up for the defect of weak precipitation of the reconstructed field.
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Zhou Ping, Fan Tianyi, Zhao Chuanfeng, Yang Xin, Wang Rumo
Available online:January 15, 2024 DOI: 10.3878/j.issn.1006-9895.2305.22206
Abstract:In this paper, a convective precipitation in the southwest of Hebei Province on May 22, 2017 is simulated using the Weather Research and Forecasting (Version4.3). By applying the satellite observed vertical profile of aerosol extinction coefficient in the model, this study quantifies the threshold values of aerosol optical depth (AOD) on affecting the precipitation rates by the aerosol radiative effect (ARE). The linkage of latent heating of microphysical processes and total advective heating to the radiative heating is discussed. The influences of ARE on temperature, moisture, relative humidity, and the thermodynamical conditions are analyzed. The results show that: (1) when AOD increases from 0.1 to 1.5, the influence of ARE on the peak precipitation rates increases and then decreases and the influence is the largest when AOD equals to 1.0. In contrast, the effect of ARE on the cumulative precipitation rates decreases and then increases, and the inhibition effect is the weakest when AOD equals to 1.0; (2) The change of radiative heating caused by ARE is accompanied by significant changes of latent heating rate of microphysical processes and total advective heating rate. The change of total heating rate is mainly determined by the latter two; (3) ARE enhances the vertical updraft in the mature stage of the convection, which is conducive to stronger convection and precipitation.
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Available online:January 15, 2024 DOI: 10.3878/j.issn.1006-9895.2307.22214
Abstract:Satellite microwave remote sensing data is one of the most important data required by global/regional assimilation system. The brightness temperatures of the upper atmosphere (middle and upper stratosphere) from microwave remote sensing are affected by many factors, and have certain errors. The accuracy evaluation of microwave remote sensing of the upper atmosphere has become an important research content due to the relatively lack of high-accuracy sounding data of the upper atmosphere. In this paper, the accuracy of the observation data of the on-orbit microwave temperature radiometers like AMSU-A、ATMS and FY-3D MWTS-2 is examined and evaluated in 2020. Three evaluation methods, i.e., comparison with radio occultation observation, with radiation transfer simulation and with cross calibration, are comprehensively used for the analysis. From different aspects, the three approaches reveal the error characteristics of the data at the upper atmosphere from various instruments, and the possible sources of the errors are analyzed. The specific deviation values of the brightness temperatures of the high-level channels are different from the three evaluation schemes, but the basic trend of the variation are consistent, that is, the high-level channels have greater noise than the middle and low level channels. In addition to the cross calibration method, the other two methods show the seasonal variation of the deviation. On the whole, AMSU-A performs better than MWTS-2 and ATMS. The temporal and spatial variation characteristics of brightness temperature accuracy at the upper atmosphere can provide reference for microwave data assimilation and climate application.
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Wang Xiaoqing, Dong Xiaobo, Yang Jiefan, Wang Shuyi, Hou Shaoyu, Zhang Xiaorui, Yan Fei
Available online:January 15, 2024 DOI: 10.3878/j.issn.1006-9895.2311.23061
Abstract:The microphysical characteristics of a supercooled cloud and the physical response of cloud seeding were analyzed using high-performance rain enhancement aircraft, ground-based S-band dual polarization radar and satellite remote sensing observations in central and southern Hebei Province on January 20, 2022. The results showed that, under the influence of the combination of southwest warm and humid air flow and easterly reflux, a large range of stratiform clouds formed with a cloud base of 1400 m and a cloud top of 2100 m, which were mainly composed of supercooled cloud droplets in the central and southern Hebei Province. Radar observation showed that after cloud seeding at a height of 2100 m, the supercooled cloud droplets rapidly froze into ice crystals, snow and a few graupel particles affected by AgI nucleation. The increase of particle size resulted in an enhanced radar reflectivity echoes in cloud-seeding regions. FY-4A satellite observations showed clear icing cloud tracks occurred after 17～19 min of cloud seeding, which can sustain for about 55 min. After cloud seeding, the supercooled cloud droplets formed ice crystal particles, which gradually grew and fell, causing the cloud top to sink and forming a cloud groove in the cloud top. Compared with the regions without seeding, the reflectance at 0.65 μm and the blackbody brightness temperature at 10.8 μm increased, the reflectance at 3.72 μm decreased within the cloud tracks.
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Available online:January 15, 2024 DOI: 10.3878/j.issn.1006-9895.2303.22248
Abstract:In February 2022, the southern China experienced persistent cold, rainy and snowy weather. The regional mean accumulated precipitation were 126.6 mm, 99.7% more than multi-year (1981~2020) average (63.4 mm), and the daily minimum temperature was 5.1°C, 2.6°C lower than the multi-year average. The analysis shows that particularly strong meridional wind vertical shear over southern China between 700 hPa and 925 hPa is a key circulation feature in February 2022. The related SST anomalies with the meridional wind vertical shear are analyzed. The results are as follows: Under the background of La Ni?a, the warming of SST over the tropical western Pacific and central North Pacific is beneficial to the deepening of the East Asian trough and northerly wind anomalies in the lower troposphere over southern China. The warming of SST over the central North Atlantic Ocean could reinforce the Ural Ridge and East Asia Trough through the Rossby wave train along the Western Europe-East Asia coast; strengthen the Siberian High and northerly winds in the lower troposphere over southern China. The warming of SST in the southeast Indian Ocean is conducive to the strengthened southern branch trough and western North Pacific anomalous anticyclone, which lead to the stronger southerly winds in the middle troposphere over southern China. The impact of SST has sub-seasonal difference. The SST over the central North Pacific and the central North Atlantic are significantly related to the Siberian High in February, which is conducive to the lower temperature in February. The SST over the southern Indian Ocean is significantly correlated with the southern branch trough in January and February, and western North Pacific anomalous anticyclone in February. The increase of precipitation in southern China from mid-January may be related to the persistent warming of SST in this area. Therefore, the SST anomalies in the above regions may be related to the sub-seasonal reversal from warm and dry to cold and wet in the winter of 2021/2022, and the persistent cold, rainy and snowy weather in February, 2022.
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ZENG Kang, MIN Jinzhong, ZHUANG Xiaoran, KANG Zhiming
Available online:January 03, 2024 DOI: 10.3878/j.issn.1006-9895.2310.23094
Abstract:In order to alleviate the common "fuzzy" problem in deep learning radar echo extrapolation prediction, a radar echo extrapolation prediction method (PhyDNetSGAN) with organic fusion of PhyDNet and frequency-domain matching generative adversarial network was developed, which can predict the combined radar reflectance factor in Jiangsu and its upstream region in the future 3h. By comparing PhyDNetSGAN, PhyDNet (without generative adversarial network), PhyDNetGAN and Sprog (improved optical flow method), the applicability of the new method in severe convection weather prediction was verified. The results show that: (1) Compared with Sprog, the deep learning method can better reflect the nonlinear evolution of strong echoes. (2) PhyDNetGAN and PhyDNetSGAN with the addition of generative adversarial network can obtain more refined radar echo extrapolation results in line with the subjective cognition of forecasters than the other two groups of experiments and alleviate the "fuzzy" problem. (3) The newly proposed PhyDNetSGAN can not only improve the forecast precision, but also better capture the form, position and central intensity of strong echoes, so as to obtain better prediction skills and extend the effective forecast time. (4) Compared with TS, the newly proposed comprehensive score index of TS, Bias and FID can better reflect the test effect of approaching forecast which is consistent with the subjective experience of forecasters.
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YAN Jinlei, ZHAO Yang, TUO Yufeng, KONG Xiangzhen, BI Lixia
Available online:December 26, 2023 DOI: 10.3878/j.issn.1006-9895.2308.23048
Abstract:Medium Range Weather Forecasts, were used to study lightning in different regions of mainland China. The relationship between lightning and convective available potential energy (CAPE), precipitation (P), convective inhibition (CIN) and relative humidity (RH) was analyzed from the spatial and temporal distribution and quantitative relationship. The results show that lightning has a good correlation with CAPE, P and CAPE×P in time and space. An appropriately small CIN and a sufficiently large CAPE are most conducive to generating lightning; The higher the CAPE, the more lightning; The smaller the inhibition energy is, the more likely it is to convection and further generate lightning. However, CIN should not be too small, because too small CIN will lead to less lightning. A low CIN value is not sufficient for lightning to occur, and the relative humidity needs to be high. Lightning activity is concentrated in the environment where RH is 60%~90%. If RH continues to increase, lightning activity will decrease. Even in high CIN conditions, with certain moisture and CAPE conditions, there can be a lot of lightning.
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Available online:December 26, 2023 DOI: 10.3878/j.issn.1006-9895.2312.23316
Abstract:Aerosol excintion is the main factor affecting atmospheric visibility. The nonlinear relationship between aerosol concentration and scattering and absorption characteristics leads to great uncertainty in the influence of aerosol on the visibility. The concentrations of reconstructed fine mass (RCFM) ranged from 1.4 to 19.4 μg m–3 and reconstructed aerosol extinction coefficients from 10.0 to 172.5 Mm–1 in the United States from 1988 to 2008 from IMPROVE (the Interagency Monitoring of Protected Visual Environments) network. The average fine particulate matter (PM 2.5) concentrations in various regions of China ranged from 14.3 to 188.3 μg m–3 from 2006 to 2018, corresponding to reconstructed extinction coefficients of 52.6–1044.0 Mm–1. The PM2.5 concentration in the U.S. region was comparable to that of Sanya, China. In most cases, sulfate was the largest contributing component to aerosol extinction, accounting for up to 77%, followed by organic matter with a maximum of 50%, while nitrate contributed more to aerosol extinction only in Southern California, exceeding 30%. The difference in extinction between the east and west was more significant than the difference in aerosol concentration because of the higher relative humidity in the east than in the west. In China, sulfate and organic matter were the main components of extinction, accounting for 21%–57% and 21%–39%, respectively, and nitrate was the main extinction component only in central China, exceeding 30%. The reconstructed extinction coefficient had both low values of overestimation and high values of underestimation (-60%–35%). The more severe the pollution, the more obvious the underestimation. Aerosol concentration and extinction level are significantly higher in China than in the United States. IMPROVE equation has obvious uncertainties to underestimate high extinction coefficient and to overestimate low extinction coefficient in China. The uncertainty will have a negative impact on the accurate implementation of air pollution prevention and blue sky program. It is urgent and significant to carry out the accurate accounting extinction of aerosol components and tracing the aerosol sources, which will provide scientific program to control the aerosol sources for improving atmospheric visibility in the various environmental climate regions.
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Available online:December 25, 2023 DOI: 10.3878/j.issn.1006-9895.2205.22059
Abstract:The development of high-resolution mesoscale weather forecast numerical models is an important way to improve the forecast of torrential rain. Regional mesoscale models, with a spatial resolution to 100m, pose great challenges to current computational resources. A feasible solution is to develop soundproof models to replace those fully compressible models. Soundproof models permit relatively larger time steps, improving the integration efficiency significantly. We developed a test version of a pseudo-incompressible model in a terrain-following mass-based coordinate (η coordinate), based on a sound-proof theory namely the pseudo-incompressible theory in 2018. Numerical tests indicate the results from the model are reliable. However, a key issue is the acoustic wave not yet excluded by the model. In this paper we improve the pseudo-incompressible model and establish a new dry air dynamic core for the pseudo-incompressible model. The most significant improvement of the governing equations of the new dynamic core is that it solves an elliptic equation for perturbation pressure, which ensures the exclusion of acoustic waves in theory. The improvement in the numerical scheme of the new dynamic core is that the time-integration scheme no longer relies on the time-split algorithm. We compared the simulation results by the improved version of the pseudo-incompressible model with those by WRF model in a dry hot bubble numerical test. It is found that the pseudo-incompressible model obtains similar dynamic and thermodynamic field distributions to those from the WRF model, and the simulated perturbation pressure time series are smooth, indicating that the acoustic waves have been removed. This is a significant improvement over the pseudo-incompressible model released in 2018.
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Available online:December 20, 2023 DOI: 10.3878/j.issn.1006-9895.2308.23075
Abstract:Based on the daily reanalysis data of the Japan Meteorological Agency (JRA55) from 1958 to 2020, the thermal budget characteristics before and after winter onset in North Asia (50°-75°N,80°-140°E) and the external forcing factors that affect winter onset are studied. The result shows that the climatological winter onset in North Asia occurs in the sixty-second pentad. Before the onset, North Asia experienced a process from drastic cooling to slow down. In this process, the diabatic cooling plays a major role, which is partially offset by the warm advection. Based on the linear baroclinic model, the diabatic cooling in the middle and high latitudes of the Eurasian continent is conducive to the formation of westerly and southerly winds in North Asia, resulting in strong local warm advection, and then partially counteracting the cooling effect of the diabatic heating itself. On the interannual time scale, the sea surface temperature anomalies in the Equatorial east-central Pacific and North Atlantic both affect winter onset in North Asia through anomalous wave train on the Eurasian continent, and they show significant signals one month and five months in advance, respectively, which has certain predictive significance. In terms of its impact on winter temperatures, the temperature in some parts of East Asia and southern China is higher (lower) in December in the early (late) year of winter onset in North Asia.
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Effect of Physical Parameterization Scheme Combined with Perturbation on Ensemble Prediction Quality
WEI LIQING, MIN JINZHONG, YANG TING
Available online:December 20, 2023 DOI: 10.3878/j.issn.1006-9895.2306.22219
Abstract:There are many parameters in the cloud microphysics scheme and the constraint relationship between the parameters is complex, so it has not been decided what parameters should be selected and how to carry out the parameter combination disturbance in the ensemble forecast. Based on WRFv4.2 model, this paper selects eight parameters of WSM6 scheme to conduct the ensemble prediction experiment of parameter disturbance for the heavy rainfall event of Meiyu front in 2020. Contrast and analyze the influence of different parameters and different disturbance range combinations on prediction, and try to jointly disturb the sensitive parameters of cloud microphysical scheme and boundary layer scheme. The results show that the combined disturbance of the 4 sensitive parameters of the cloud microphysics schemes has the best performance in the prediction test, which reduces the False Alarm Rate of torrential rain probability forecast, and improves the spread skills of humidity field, zonal wind, temperature field in low level and meridional wind in middle troposphere. The combined disturbance of the raindrop truncation parameter and the maximum of the cloud ice diameter presents a synergistic resonance effect, which can effectively improve the ensemble prediction effect. However, combined perturbations between graupel truncation parameters, graupel density and truncation parameters show that disturbance energy does not increase with the increase of disturbance parameters, and the antagonism between parameters will restrict the improvement of ensemble forecasting skills. The disturbance of three parameters in the MRF boundary layer scheme has significantly improved the ensemble prediction skill of low layer humidity field, and the combined disturbance of three parameters is better than that of a single disturbance; At the same time, joint perturbation of the cloud microphysical parameter perturbation scheme and boundary layer parameter perturbation scheme can achieve the best effect. It shows that the selection of parameter and the range of the disturbance can affect the effect of the ensemble forecast, a collaborative relationship between the parameters of the combination is easy to obtain a better forecast effect, while parameter combinations with antagonistic effect show negative skills. Multi parameter disturbance considering the dependency relationship between parameters and the range of disturbance is more conducive to the improvement of ensemble prediction effect, which provides a valuable reference for the selection of parameters in parameter disturbance in the future.
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WANG Tianshu, NIU Shengjie, WANG Ying, ZHAO Junjie, LIANG Mian, WANG Yuan, FAN Dongliang, YANG Feiyun, WANG Tao, ZHANG Hongwei, Yuan Wei
Available online:December 20, 2023 DOI: 10.3878/j.issn.1006-9895.2309.23070
Abstract:Comprehensive fog observation campaigns at Lushan Meteorological Bureau of Jiangxi Province were conducted with a fog drop spectrometer and an automatic weather station in January and December of 2016, respectively. This study investigated the physical characteristics (macro and micro) of supercooled fog and elucidated its evolution mechanism. Combining observational data with NCEP 1°×1° reanalysis data, the macro and micro physical characteristics of two supercooled fogs cases (case 1 on January 16-17, 2016, while case 2 on December 25-27, 2016) were analyzed. Our results revealed that the evolutions of the two supercooled fogs were strongly correlated with the movement of cold front. From the formation stages to the development stages, the dominated wind direction below 800 hPa changed from southwest to northerly, the front edge of the cold front arrived at the study area, and the temperature near the surface decreased sharply in both cases. At the mature stages of the two supercooled fogs, the rain stopped at the near-surface and the wind force weakened, meanwhile, the front inversion layer appeared in case 2. During the dissipation stages, the wind direction in 900-500 hPa changed into north in both cases and the wind speed below 800 hPa increased obviously. For micro characteristics, the average droplet spectra exhibited bimodal distributions in both cases, with the main peaks at 4.9 μm. However, the secondary peaks were at 8.9 and 11.0 μm in case 1 and case 2, respectively. Both cases presented instantaneous droplet spectra with the main peaks between 10 to14 μm, and the frequency were 12.4% and 46.3% in case 1 and case 2, respectively. Both cases had a transition from warm fog to supercooled fog. Compared with the warm fog, the number density of supercooled fog droplets in each size increased, especially for droplets with particle size below 14 μm. The correlation between fog droplet number concentration and average diameter in the whole process of case 1 was weak, which may be affected by factors such as fog droplet collision-coalescence and droplet competition for water vapor. Case 2 showed positively correlation among the fog droplet number concentration, average diameter and water content in the whole process, which indicated that the fog process was dominated by condensation nuclei activation and condensation growth. The strong low-level jet in southwest, the obviously decreased temperature in near-surface, and the inversion layer were all found in case 2, resulting in the wider droplet spectrum, the more prominent peak between 10 and 14 μm particle sizes in droplet spectrum, moreover, higher values of number concentration, average diameter, and water content comparing with case 1.
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HUANG Yu, WEN Dian, XU Huanbing, HUANG Mengyu, LU Xu, XU Liren
Available online:December 18, 2023 DOI: 10.3878/j.issn.1006-9895.2307.23013
Abstract:In this paper, two response characteristics of detonation dynamic disturbance experiments conducted in Xiangshan and Zhengyangmen, Beijing were studied based on high-precision laser wind radar, and using the wavelet analysis method to investigate the dynamic characteristics of natural wind field disturbance response caused by shelling. The results show that detonation has an impact on wind field, both experiments (<300m) showed a synchronous wind direction turning phenomenon with the start and end of detonation. Detonation dynamic disturbance produced Reynolds stress effect and formed secondary circulation vortex. Its influence characteristics are reflected by the dominant oscillation of wavelet analysis. Detonation stimulated multi-scale structure of vortex, which is located at height of 150-250m and decayed with height. The impact of detonation dynamic disturbance in both experiments was the strongest in vertical wind direction, resulting in a largest and stable vortex (with large scale, large amplitude and long period，barely variation with height); The horizontal wind direction took the second place, and the larger vortex in lower layer quickly turned into smaller in upper layer as height increased; The horizontal wind speed was the weakest, forming smallest and weakest vortex (with small amplitude and short period). The intensity and form of shelling had a significant impact on characteristics of wind field disturbance. The salute was small, the launch was relatively divergent, the secondary flow field formed was weak, and its maintenance and supplement effect on vortices was weak. The above shows that the non-uniform disturbed airflow field can excited asymmetric vortex pairs, and the occurrence of vortex pairs will cause the change of the dominant wind direction, accompanied by the change of the moving scale components, forming updrafts, breaking the original balance, and may make precipitation conditions more favorable, thereby achieving the effect of artificial weather modification.
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ZHANG Fanghua, KONG Qi, YUAN YI, RAN LINGKUN, SHEN DONGDONG
Available online:December 18, 2023 DOI: 10.3878/j.issn.1006-9895.2307.22225
Abstract:The extreme characteristics of the "21.7" rainstorm in Henan Province from July 19 to 21, 2021, including the impact range, duration, rainfall intensity, and cumulative precipitation, were analyzed using national precipitation data. Based on ERA5 reanalysis data and the generalized Omega equation, key physical factors affecting vertical movement were studied, and the differences from the "75.8" rainstorm were discussed. The results show that about 10% of the stations in Henan Province accumulated precipitation exceeding 500mm during the "21.7" rainstorm, with an average precipitation of 92.8mm on the 20th July 2021, ranking first since 1961. On that day, the hourly precipitation at 16:00-17:00 in Zhengzhou (201.9mm) broke the extreme hourly record in Chinese Mainland. Both the "21.7" and "75.8" rainstorm were accompanied by the transport of water vapor from typhoon flows. The water vapor of the "21.7" rainstorm mainly came from the vapor transport of the southeastern jet stream between Typhoon "Fireworks" and the sub-high, while the "75.8" rainstorm had two water vapor channels: the southwest airflow from the Indian Ocean and the southeast airflow from the Western Pacific. In both rainstorms, the total Q-vector divergence anomalies of the generalized Omega equation corresponded to areas of strong vertical movement. The vertical velocity intensity and total Q-vector divergence intensity of the "21.7" rainstorm was slightly weaker than that of the "75.8" rainstorm. The vertical motion of the "21.7" rainstorm was mainly causd by the combination of low-level dynamics and thermal forcing. For the "75.8" rainstorm, vertical motion was primarily caused by the middle-low level thermal forcing and low-level dynamic forcing. The different distribution of vertical motion in the spatial may be one of the reasons why Zhengzhou area is more prone to the occurrence of short-duration intense precipitation with low centroids and high efficiency.
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Longguang Chen, Chen, Chen, Xiangde Xu
Available online:December 18, 2023 DOI: 10.3878/j.issn.1006-9895.2303.23017
Abstract:The western side of the Sichuan Basin is one of the regions with the highest frequency of extreme heavy precipitation events (HPEs) in China. However, due to the complexity of terrain and atmospheric circulations systems, the formation mechanism of HPEs remains elusive. Based on the gauged data by China Meteorological Administration from 2001 to 2020, GPM-IMERG precipitation and ERA5 reanalysis data, we selected 100 extreme HPEs in the west of Sichuan Basin, and classified these HPEs into three categories with K-means clustering method. Then, the anomalies of atmospheric circulation and its evolution with respect to different category of HPEs are explored. The results show that, during the period of precipitation, the geopotential height is characterized by a positive anomaly at the upper-level (200hPa) and negative anomaly at the lower-level (850hPa), together with the enhanced vertical wind speed, a "top-cold and bottom-warm" atmospheric temperature structure, and the increased water vapor transport departing from the low latitude ocean area. However, their atmospheric circulations configuration, including the South Asian High, the Western Pacific Subtropical High, and the westerly jet in upper level, shows obvious difference and plays a dominant role in in shaping the precipitation formation of different types and associated water vapor transport: For category 1 HPEs ranked the highest frequency of occurrence, its associated water vapor transport mainly comes from the Bay of Bengal and the South China Sea, which controlled both by the Indian monsoon and the East Asian monsoon. As to category 1, HPEs occurs with the strengthened WPSH, and its water vapor mainly comes from the South China Sea, while the water vapor transport from the Bay of Bengal is restricted. When it comes to the category 3, its water vapor transport mainly controlled by the East Asian monsoon. Prior to the occurrence of HPEs, it can be found that the Rossby wave action shows an increasing trend, the atmospheric vertical wind speed increase significantly, and the temperature anomaly was more significant. These features are conducive to the occurrence of extreme precipitation events. The results also indicates that the changes in WPSH position and intensity on synoptic time scales are better indicators for the prediction of heavy precipitation formation compared to SAH.
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Institute of Plateau Meteorology
Available online:December 18, 2023 DOI: 10.3878/j.issn.1006-9895.2311.23092
Abstract:Based on the ERA5 (0.25° × 0.25°) hourly reanalysis data, this paper analyzes two different high-impact Southwest Vortex (SWV) processes with long-distance movement and stagnation over local area. It is suggested that two physical variables, the low- to mid-level convergence and pseudo-equivalent potential temperature, are the key factors influencing the development and evolution of the vortex. According to these findings, a vortex development index is defined in this study. By comparing the vortex development index with the evolution of the SWV and precipitation, we found that: (1) the vortex development index could indicate the development and evolution trend of the intensity and position of the vortex, whether it is a long-distance moving or a local stationary SWV process. The index could also reveal the occurrence of other weak closed lows or multi-core vortices during intense vortex events, as well as the moving mechanism of the SWV. (2) The vortex development index not only indicates the intensity and coverage area of vortex precipitation but also reflects the coexistence phenomenon between the SWV and precipitation, thereby providing a possible explanation for both the "rain-induced vortex" and the "vortex-induced rain" phenomenon. Results of this study suggest the positive significance of the vortex development index in the forecast of both the precipitation distribution and the position of the precipitation center of the high-impact SWV heavy rainfall events.
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Available online:December 07, 2023 DOI: 10.3878/j.issn.1006-9895.2306.23319
Abstract:Based on a brief review of the research progress of surface potential vorticity, this paper introduces the calculation of potential vorticity and its generation under complex terrain, and the research progress on the source of potential vorticity and potential vorticity circulation in recent years, focusing on the particularity of the surface potential vorticity on the Tibetan Plateau and its important influence on weather and climate. It is clarified that for adiabatic and frictionless atmospheric motion, the structural recombination of the potential vorticity itself (potential vortex reconstruction) can cause the development of vertical vorticity, which can excite the formation of plateau vortex in summer and make the eastern part of the plateau an important source of surface vorticity in winter. Based on the derived equation for the vertical motion associated with isentropic displacement () and including diabatic heating, it is further demonstrated that the eastward propagation of the positive vorticity created on the Tibetan Plateau along the westerly wind will cause the development in the downstream area of cyclonic vorticity, southerly wind, and upward motion in the lower troposphere, resulting in the increase of potential vorticity advection with altitude, which stimulates the development of extreme weather and climate events. It was pointed out that the diurnal variations of surface heating and latent heat release at the cloud bottom over the Tibetan Plateau significantly affect the diurnal variation of the potential vorticity near the surface, resulting in the development of the low-vortex and precipitation system over the Tibetan Plateau from late afternoon to night. It is proved that compared with the traditional surface sensible heating index, the surface potential vorticity index of the Tibetan Plateau can better characterize the seasonal changes of local precipitation, and is more closely related to the Asian summer monsoon precipitation. The concept of potential vortex circulation (PVC) is also briefly introduced. It is pointed out that since the change of convergence of PVC across the close boundary of an area is directly related to the change of potential vorticity of the area, in order to maintain the relative stability of the total potential vorticity in the northern hemisphere, the change of PVC on the trans-equatorial plane and the change of surface PVC must complement each other, so the change of the potential vortex circulation on the trans-equatorial plane can be considered a window for monitoring near-surface climate change. The near-equatorial air-sea interaction can directly cause the change of vertical shear of the zonal wind on the vertical plane across the equator, stimulate the trans-equatorial PVC anomaly, and thus affect the climate change near the surface of the northern hemisphere through the change of PVC in the atmosphere and the regulation of the Tibetan Plateau. The analysis shows that PVC analysis opens up a new way for establishing the link between tropical and extra-tropical atmospheric circulation changes, and has broad application prospects.
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Available online:December 07, 2023 DOI: 10.3878/j.issn.1006-9895.2311.23323
Abstract:In recent years, the disastrous weather, such as heavy rainfall and severe convection occur frequently in China, and vortices is one of the important weather systems that produce these disastrous weathers. In order to improve the understanding and prediction accuracy of the mechanism of vortices, and their producing heavy rainfall and severe convective weathers in China, this paper mainly summarizes the important research results of three types of vortices (Tibetan Plateau vortex, Southwest vortex and Dabie vortex) along the Yangtze River basin, Northeast cold vortex and Central Asian vortex in northern China in recent ten years. This paper mainly reviews the identification methods, statistical characteristics of spatial and temporal distribution, three-dimensional structure of these vortices, as well as the formation mechanism of heavy rainfall and severe convection weathers associated with the vortices in the past ten years. Finally, a brief discussion and outlook are given on the future directions in research and forecasting related to vortex systems and their weathers.
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Zheng Fei, Zhang Xiaojuan, Cao Tingwei
Available online:December 07, 2023 DOI: 10.3878/j.issn.1006-9895.2311.23325
Abstract:Under the influence of global warming, the continuously growing Marine Heatwaves (MHW) has a serious impact on the climate system and the social economy, of which the Western Pacific Warm Pool area is a typical area of MHW characteristic changes. Based on the MHW database, the National Centers for Environmental Prediction (NCEP) atmospheric and oceanic reanalysis data, the chlorophyll-a concentration data provided by the National Aeronautics and Space Administration (NASA) Aqua satellite and the biogeochemical Argo floats, by using statistical methods such as composite analysis and singular value decomposition (SVD), we explore the evolution characteristics, physical mechanisms and ecological impacts of MHW in the Western Pacific Warm Pool from 2020 to 2022. The results show that MHW properties in the Western Pacific Warm Pool region have increased significantly in the past 30 years and it is closely related to the continuous La Ni?a events. Under the background of multi-year La Ni?a events from 2020 to 2022, the frequency of MHW in the Western Pacific Warm Pool reached the highest in the world, and the coverage area, frequency, total days and cumulative intensity of MHW are the most notable since 1982. By using the mixed layer heat budget equation in the Western Pacific Warm Pool region, it is shown that the occurrence of the strongest MHW during the period 2020 to 2022 is mainly dominated by the downward shortwave radiation term in the net flux and the latitudinal advection term in the marine dynamic processes. In addition, we also revealed that the MHW properties and marine ecological indicator chlorophyll-a concentration show a negative correlation on the spatial and temporal scales in the Western Pacific Warm Pool region, especially the MHW events during 2020-2022 caused the significant decline of overall phytoplankton biomass in the upper ocean of the region.
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Huizhi Liu, Qun Du, Lujun Xu, Yang Liu, Xiaoni Meng, Yamei Shao, Yingqi Zheng
Available online:November 29, 2023 DOI: 10.3878/j.issn.1006-9895.2309.23315
Abstract:The Hengduan Mountains situated in the southeast margin of the Tibetan Plateau is in the conjunction area of the south Asia monsoon and southeast Asia monsoon, and it is also the heating area and sensitive area of the atmospheric change. It is of great importance for the understanding of the key processes of the atmospheric water resource in the Tibetan Plateau to investigate the effects and its parameterization schemes of the interaction between the land surface and the atmosphere on the water and energy exchange processes in this region. It is introduced about the land-atmospheric filed experiments developed in this area based on the continuous eddy covariance measurements. It is also analyzed about the patterns of the exchange process between the wetland/ lake/ grassland surfaces and the atmosphere in Erhai lake, Lijiang alpine grassland and Tengchong Beihai wetland land surface process observation sites. In addition, the characteristics of local circulation simulated with numerical models are also investigated in complex mountainous areas. The characteristics of land-atmosphere surface exchange process and their influencing factors for different types in the southeastern edge of the Tibetan Plateau and Hengduan Mountains have been preliminarily identified and revealed. The main conclusions are as follows: the carbon and water exchange processes in alpine meadows in the southeastern edge of the Tibetan Plateau are significantly influenced by precipitation distribution. In addition to meteorological factors, the carbon and water exchange in "floating blanket" wetlands with grass floating on the surface like blanket for whole year is also affected by changes in underlying surface vegetation and water proportion. The influencing factors of carbon and water exchange processes in different types of ecosystems vary at different time scales. Wind speed is always a key factor influencing latent heat and CO2 exchange in lakes, while precipitation also has a significant impact on CO2 flux in lakes at longer time scales. Furthermore, the complex terrain in the southeastern edge of the Tibetan Plateau has a significant impact on the ecosystem carbon and water exchange processes. Different types of local circulations generated by complex terrain have different effects on the carbon and water exchange processes of ecosystems
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Yang Luping, Wu Qigang, Hu Yuantao, Hu Aixue
Available online:November 28, 2023 DOI: 10.3878/j.issn.1006-9895.2310.23100
Abstract:Based on the latest satellite-derived sea ice concentration (SIC) data, this study investigates the seasonal and spatial characteristics of Antarctic sea ice trends from 1979 to 2014, and examines the relative contributions of the Interdecadal Pacific Oscillation (IPO) and Atlantic Multidecadal Oscillation (AMO) phase shift to the Antarctic sea ice trend and associated mechanisms. Results indicate that SIC in the Ross Sea and the Indian Ocean showed increasing trends in the four seasons, and the annual and seasonal Antarctic sea ice extent (SIE) exhibited significant increase trends from 1979 to 2014. During the warm seasons (December-May), SIC decreased significantly in the Amundsen-Bellingshausen Seas and decreased in the Weddell Sea ice, resembling a positive phase of Antarctic Dipole (ADP). During the cold seasons (June-November), the SIC trends in Amundsen-Bellingshausen-Weddell Seas showed a negative phase of ADP. The shift of IPO from a positive to negative phase during 1979-2014 deepened the Amundsen Sea Low (ASL) by exciting Pacific-South America (PSA) atmospheric teleconnection and significantly contributed to the negative phase of ADP in the austral winter and spring. During the austral spring, the shift of AMO from a negative to positive phase during 1979-2014 enhanced the ASL through the excitation of the Rossby wave and PSA wave train across the South Pacific basin and weakened the Ekman suction that would advert less warm water upward, contributing to the negative ADP and increased sea ice trend in the eastern Ross Sea, Amundsen Sea and Indian Ocean and explaining about 75% of the austral spring Antarctic SIE increased trend. In the austral summer, the above IPO and AMO phase transitions might have enhanced the Southern Annular Mode (SAM) and thus contributed to the increased trend of Antarctic sea ice. Our results suggest the seasonality and regionality of impacts of the IPO and AMO phase shifts on Antarctic sea ice trends through the atmospheric teleconnection mechanisms.
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Tian liqing, Li Shuwen, Qiu Xiaobin, Ran Lingkun, Shen Dongdong
Available online:November 24, 2023 DOI: 10.3878/j.issn.1006-9895.2308.22111
Abstract:Extreme rainstorm in Henan Province, China, from July 19 to July 21, 2021, was accompanied by a lot of low-level jet (LLJ) activity. The horizontal motion equation, the kinetic energy equation, and the geopotential height gradient equation in isobaric coordinate system are used in this research to investigate the key physical factors influencing the evolution of LLJ using ERA5 data. According to the investigation, the LLJ center initially formed at 925hPa near Zhengzhou, developed and intensified to the northwest vertically, and then its core location was elevated to 850hPa and 700hPa, successively. The horizontal gradient of the geopotential height had a significant impact on the local change of the zonal and meridian winds of the LLJ. The mountainous territory to the west of Zhengzhou had a low value system of geopotential height, while the plain region to the northeast of Zhengzhou had a geopotential height system with a high value. The two of them generated a strong zonal gradient force of geopotential height near Zhengzhou, which, in conjunction with the zonal east wind, driving the growth of kinetic energy of LLJ. The anomalous distribution of geopotential height was mostly attributable to surface geopotential height and the vertical integration of near-surface virtual temperature. The calculation of equation of the zonal gradient of geopotential height revealed that the vertical advection of potential temperature resulting from the zonal gradient of vertical velocity and the zonal gradient of diabatic heating were the principal forcing terms for the local variation of the zonal gradient of geopotential height. The relatively low temperature region in the mountainous region and the relatively high temperature region in the plain region had a significant effect on the development and evolution of the LLJ.
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Multi-scale effects of Tibetan Plateau-Indian Ocean thermal contrast on South Asian monsoon activity
Available online:November 24, 2023 DOI: 10.3878/j.issn.1006-9895.2310.23324
Abstract:The land-sea thermal contrast is the fundamental driving force for the Asian summer monsoon formation and evolution. Tibetan Plateau-Indian Ocean thermal contrast is a crucial factor influencing South Asian monsoon activity. This article reviews and summarizes the relevant research results about the impacts of the Tibetan Plateau-Indian Ocean thermal contrast on South Asian monsoon activity at different time scales, including sub-seasonal, seasonal, inter-annual, and inter-decadal scales. On the sub-seasonal scale, the main focus is on the influence of the thermal contrast on the onset of the South Asian monsoon. On the inter-annual scale, the emphasis is on the indicative significance of the thermal contrast for the interannual variation of monsoon intensity. On the inter-decadal scale, the inter-decadal variations in the relationship between the thermal contrast and South Asian monsoon precipitation are examined. Meanwhile, the article discusses some issues that need further research in this field.
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Available online:November 24, 2023 DOI: 10.3878/j.issn.1006-9895.2311.23322
Abstract:Waveguide teleconnections are quasi-stationary planetary waves propagating along the jet stream waveguide. They play an essential role in the maintenance and evolution of atmospheric circulation, and their abnormal activities are often associated with extreme weather and climate events. Studying the variation and mechanism of waveguide teleconnections at different timescales can not only deepen our understanding of the dynamics of atmospheric circulation but also serve as a scientific basis for weather forecasting, climate prediction, and even climate projection at corresponding timescales. According to the dynamical property of the jet stream waveguide, the atmospheric waveguide can be divided into the subtropical jet waveguide, which is maintained essentially by the barotropic effect, and the polar front jet waveguide, which is primarily maintained by the baroclinic effect. This paper focuses on the waveguide teleconnections in the boreal summer over the Eurasian region, when and where waveguide teleconnections are the most active. It first reviews the history and theory of waveguide teleconnection and then summarizes some recent advances in waveguide teleconnections along the subtropical jet and polar front jet, including their formation conditions, dynamic mechanisms, climate impacts, and future changes. Finally, it discusses some possible issues that deserve future investigation.
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Available online:November 20, 2023 DOI: 10.3878/j.issn.1006-9895.2305.23304
Abstract:El Ni?o-Southern Oscillation (ENSO) influences global weather and climate through teleconnection patterns. In tropical regions, ENSO can induce precipitation and sea surface temperature anomalies over remote ocean basins by influencing tropical tropospheric temperatures. In extratropical regions, ENSO can pose climate impacts over regions such as North America and Asia through the excitation of quasi-stationary Rossby waves. The background mean-state fields are of vital importance to ENSO"s tropical and extratropical teleconnections. On one hand, the background mean-state atmospheric circulations can influence the position and intensity of ENSO teleconnection wave trains through barotropic and baroclinic energy conversion. On the other hand, the tropical background mean-state sea surface temperature and convection fields can influence ENSO"s tropical teleconnection processes through the adjustment of moist static energy distribution. These studies suggest that analyzing energetic processes can help to understand the mechanisms through which the background mean-state fields influence ENSO teleconnections. The present study reviews the progress in energetic analysis researches on the impacts of the background mean-state fields on ENSO"s tropical and extratropical teleconnections in recent decades. Based on it, this study will further review the potential changes of ENSO teleconnections under global warming, and propose some important scientific questions that need to be studied in the future.
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Available online:November 20, 2023 DOI: 10.3878/j.issn.1006-9895.2309.23305
Abstract:This paper provides an overview of recent (2018-2023) progresses in the research filed of the Arctic-Eurasian midlatitude linkage and its association with Arctic sea ice loss. The progress includes the following aspects: (1) There is a substantial understanding of the contribution of Arctic sea ice melting in an extreme snowfall event in Europe, which cannot be explained by the mechanism that Arctic sea ice variations affect atmospheric circulation proposed in previous studies. (2) The response of winter Asian regional temperatures to the continuous melting of Arctic sea ice exhibits significant low-frequency oscillation characteristics. The continuous melting of Arctic sea ice is conducive to the alternating occurrence of warm Arctic-cold Eurasia (2004/05-2012/13) and warm Arctic-warm Eurasia (2013/14-2016/17). In the war Arctic-cold Eurasia phase, the enhanced Arctic-midlatitude connection was observed, while in the warm Arctic-warm Eurasian phase, the linkage between the Arctic and East Asia weakened. However, the mechanism by which sea ice melting affects the strength of the Arctic-Eurasian connection is unclear. (3) At summer mean and sub-seasonal time scales, summer heatwaves in the mid- and low-latitudes of East Asia are dynamically linked to the simultaneous cold anomalies in the mid- and low-troposphere over the Arctic. Arctic summer cold anomalies are conducive to not only slowing down Arctic sea ice melting, but also provide a precursor signal for predicting East Asian winter monsoon. (4) Arctic sea ice loss does not produce substantial impact on summer precipitation variability in the region south to North China. (5) Although there are many studies stressing the important roles of the troposphere-stratosphere interactions in linking Arctic sea ice loss to weather events and climate variability in the midlatitudes, the causal-effect linkage is still weak, and the uncertainty of the impact of the stratosphere process on weather events and climate variability is greater than that of the troposphere process. (6) It is no longer practical to distinguish the different roles of Arctic sea ice forcing and atmospheric internal variability in weather events and climate variability. In the future, more attention should be paid to the role of Arctic sea ice melting in resulting low-frequency atmospheric circulation variability, as well as the impacts of the spatial distribution differences in Arctic sea ice anomalies and different abnormal amplitudes. Additionally, quantitative research is also needed to explore the roles of Arctic sea ice melting in extreme weather and climate events.
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fanke, tianbaoqiang, daihaixia
Available online:November 20, 2023 DOI: 10.3878/j.issn.1006-9895.2308.23312
Abstract:Large inter-month variations of summer precipitation tend to cause alternations or transitions of extreme drought and flood in China, but seasonal averages may cover alternations on monthly scale, and affect the prediction skills on seasonal scale. Thus, it is necessary to improve the forecast of monthly climate which contribute to the enhancement of predictions on seasonal scale. This study focuses on the real-time predictions of monthly precipitation at 160 stations in China during the summer season (June, July, and August) with the year-to-year increment method and the field information coupled pattern method, and further calculate the seasonal precipitation with monthly predictions. The information from preceding observations and simultaneous predictions from the second version of Climate Forecast System (CFSv2) are considered. Consequently, the observed sea surface temperature (SST) over the mid-high latitude of the South Pacific in December, the observed sea ice concentration (SIC) in the critical region of the Arctic in January, and the simultaneous SST from CFSv2 released in February are selected as predictors to develop the downscaling model. Prediction models based on individual predictors are established firstly to evaluate the prediction skills of different predictors, and then the singular value decomposition (SVD) error correction method is applied to diminish the errors of downscaling models. The optimized ensemble scheme is also adopted to synthesize hybrid downscaling models for summer precipitation over China on monthly scale with higher stability, and further seasonal prediction is conducted with results on monthly scale. The re-forecast results during the period 1983?2022 showed that the hybrid downscaling models derived from the optimized ensemble scheme exhibit comprehensive prediction skills compared with single-predictor models. The percentages of stations, at which the time anomaly correlation coefficients of re-forecast results are larger than the 90% confidence level, count for 90%, 88%, and 82% respectively for June, July, and August. The mean values of the spatial anomaly correlation coefficients are respectively 0.39, 0.40, and 0.39, passing the 99% confidence level. For real-time prediction, the hybrid downscaling models perform well at both monthly and seasonal scales during 2020?2022, when summer precipitation situations are anomalous and different from each other under similar La Ni?a events. The averaged Ps scores of real-time predictions are respectively 75, 75, and 70 for precipitation in June, July, and August. The Ps scores for summer precipitation derived from monthly predictions are 72, 76, and 73 from 2020 to 2022, which are higher than the multi-year-averaged Ps score of real-time forecasts. Hence, seasonal predictions derived from effective monthly forecasts would improve the prediction skills of climate predictions on monthly–seasonal scale.
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俞永强, An bo, Liu Hai Long, Bao Qing, Lin Peng Fei, He Bian, Zheng Wei Peng, Luan Yi Hua, Bai Cong Rong
Available online:November 20, 2023 DOI: 10.3878/j.issn.1006-9895.2308.23317
Abstract:One of the major trends in the development of climate system models today is to improve the ability to simulate multi-scale interaction processes and extreme events in the climate system by increasing the spatial resolution of climate models. In the past five years, scientists from the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS) have developed and improved the 25 km resolution atmospheric circulation model FAMIL2.2 and the 1/10 degree resolution ocean circulation model LICOM3.0, and established the high resolution climate system model FGOALS-f3-H based on them. A large number of numerical simulations and climate predictions have been carried out using the above high-resolution models, including the high-resolution model comparison project (HighResMIP) of the sixth phase of the international Coupled Model Inter-comparison Project (CMIP6), and the establishment of an ocean circulation prediction system (LFS). Preliminary diagnosis and analyses show that compared to low-resolution models, high-resolution models can better simulate important weather and climate events such as typhoons, extreme precipitation, oceanic mesoscale eddies, and mesoscale sea-air interaction processes.
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Wang Yiming, Li Xiaohan, ZhangYi, Yuan Weihua, Zhou Yihui, Li Jian
Available online:November 17, 2023 DOI: 10.3878/j.issn.1006-9895.2309.22223
Abstract:Medium-range forecasting experiments were conducted using the 0.125-degree weather forecast model configuration of the domestically developed Global-to-Regional Integrated forecast SysTem model (GRIST). The precipitation forecast performance for the baseline version of GRIST was evaluated by comparing with the ERA5 reanalysis data, satellite observation data (GPM) and two global numerical weather prediction models. In addition, sensitivity of GRIST to different dynamic configurations was explored. The results show that GRIST under cold start can simulate the global 500hPa circulation well. Its performance on 500hPa geopotential height anomaly correlation coefficient (ACC500) is comparable to that of the Global Forecast System(GFS) of the National Centers for Environmental Prediction(NCEP). In terms of precipitation simulation, GRIST reproduced the spatial distribution of global mean precipitation overall consistent with the observation. With the increase of integration time, the model presents larger systematic precipitation wet biases than NCEP-GFS over the intertropical convergence zone (ITCZ) and the south slope of the Tibetan Plateau. Based on the analysis of precipitation intensity and frequency, these wet biases are likely due to the overestimation of precipitation frequency. Six key regions are selected to investigate the forecasted precipitation intensity-frequency spectrum and its diurnal variation. The intensity and frequency structure of “heavy precipitation” is better simulated by GRIST than that in NCEP-GFS. The simulation performance of diurnal variation of precipitation is generally reasonable, but an overestimation and advance of precipitation peak was found in several areas. The hydrostatic and non-hydrostatic dynamical cores of GRIST are highly consistent in the 0.125-degree resolution weather prediction, and the vertical 60 layers experiments have certain added value on simulating circulation and precipitation compared with the 30 layers.
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Jia Long, Yu Shanshan, Xu Yongfu
Available online:November 17, 2023 DOI: 10.3878/j.issn.1006-9895.2311.23309
Abstract:Ozone pollution is a significant environmental problem for some cities in China at present. The ozone formation depends on the chemical reactions affected by the atmospheric physical process and various meteorological conditions, so it is necessary to study near-ground ozone pollution from both chemical and physical aspects. This study analyzed the physicochemical processes of photochemical pollution in Huairou, an urban city in Beijing, in autumn 2022, by combining field observations and the Eulerian photochemical box model simulations. The daily variation characteristics of meteorological factors, such as temperature, relative humidity, and wind speed, and the concentrations of ozone and its precursors, volatile organic compounds (VOCs) and nitrogen oxides (NOx, x=1, 2), are determined. The results of source analysis show that the primary sources of VOCs were traffic emissions (46%), plant sources (25%), solvent evaporation (23%) and combustion process (9%). The contribution of ozone from regional transport and reactions of local VOCs was obtained based on the Euler photochemical box model. The results show that ozone was mainly from horizontal transport (> 74%) during the strong north wind prevailing period. During weak south or southeast winds, O3 was formed primarily by VOCs and NOx photochemical reactions. According to the ozone formation potential of VOCs, alkenes contribute the most to ozone formation, accounting for 67%, followed by aromatics (16%). Sensitivity analysis shows that ozone formation is most sensitive to physical factors, such as light intensity, temperature and boundary layer height; meanwhile, reactive alkenes are the most sensitive among VOCs. Finally, O3 pollution control strategies are suggested based on the EKMA curves.
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Available online:November 17, 2023 DOI: 10.3878/j.issn.1006-9895.2311.23318
Abstract:Atmospheric Oxidation Capacity
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Liang Wu, Tao Feng, Ronghui Huang
Available online:November 08, 2023 DOI: 10.3878/j.issn.1006-9895.2310.23321
Abstract:This paper provides an overview of the theoretical solutions for shallow water equations and the characteristics of tropical waves. It also presents systematic methods for identifying equatorial waves from observations. Recent advancements in tropical wave observational studies have revealed several mechanisms that affect tropical wave evolutions, such as wave-flow interaction, wave-cumulus convection interaction, and moisture mode. Local large-scale circulation and cumulus convection play a critical role in controlling the structure, intensity, and movements of tropical waves. This paper also reviews the impact and mechanism of tropical waves on the formations and tracks of tropical cyclones. By examining tropical waves, the multiscale variation of tropical cyclone activity can be explained well. However, further research is necessary to address scientific problems related to atmospheric tropical waves to advance tropical atmospheric dynamics.
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Available online:November 08, 2023 DOI: 10.3878/j.issn.1006-9895.2310.23302
Abstract:This paper is written to commemorate the 10th anniversary of our mentor-academician Ye Duzheng’s pass away and his great contributions to the development of atmospheric sciences in China and Institute of Atmospheric Physics, Chinese Academy of Sciences. This paper aims to make a brief review of his main contributions to the atmospheric sciences. Over more than 70-year research career, he proposed the theory of energy dispersion of Rossby wave, which has been one of classical theories of Dynamic Meteorology. Moreover, he established the theory of atmospheric general circulation over East Asia and the Tibetan Plateau Meteorology. Especially, he proposed a scale theory regarding the adaptation process of atmospheric motion and the new concept of adaptation to global warming. Besides, this paper provides an overview of his outstanding contribution to the development of Institute of Atmospheric Physics, Chinese Academy of Sciences and his serious and careful spirit of scholarship.
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Available online:November 08, 2023 DOI: 10.3878/j.issn.1006-9895.2310.23313
Abstract:Robust warming and frequent extremely high sea temperature events (marine heatwaves, MHWs) have been observed in the coastal China seas (CCS) over the past decades, causing a series of ecological disaster, including mass mortality of marine organisms and outbreaks of harmful algal blooms. This paper presents a comprehensive review of the research progress involving the warming and marine heatwaves in the CCS, including the characteristics and causes of long-term warming trend and MHWs, as well as their ecological impacts and adaptation strategies. Under the combined influences of the East Asian monsoon and Kuroshio, the sea surface temperature (SST) in the CCS, especially in the East China Sea (Bohai, Yellow and East China Seas), has shown an enhanced response to global warming, with annual mean increases of 1.02 ±0.19°C and 1.45±0.32°C during the period of 1960-2022, respectively, with significant inter-decadal and inter-annual variability. In addition to the influence of large-scale air sea interaction such as ENSO and PDO, SST changes are also directly affected and jointly affected by the East Asian Monsoon changes and the Kuroshio meridional transport. The ocean warming has caused rapid northward migration of geographic isotherms and seasonal phenological changes (spring arrives earlier and fall begins later than normal), resulting in the changes in the growth rhythm, geographic distribution, community structure and ecological service functions of marine organisms. Frequent extreme MHWs have caused devastating disasters to some marine ecosystems such as coral reefs and aquaculture. In the future, the mid-high latitudes of CCS will be simultaneously exposed to the enhanced warming, deoxygenation, acidification, and reduced productivity; and sever climate tipping points of marine ecosystems such coral reef ecosystems in the South China Sea are very likely to triggered in the near future. There is an urgent need for in-depth research on the physical processes and predictability of marine heatwaves, as well as the forecasting and early warning systems. Furthermore, transformative climate action measures should be developed to enhance the climate resilience of ocean systems, and strong mitigation measures need to be taken as soon as possible to slowdown global warming.
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Available online:November 08, 2023 DOI: 10.3878/j.issn.1006-9895.2310.23310
Abstract:Among the factors that influencing the East Asian summer monsoon (EASM), tropical sea surface temperature (SST) is the main reason for the variation of the East Asian summer monsoon system. In recent decades, the studies on the influences of the tropical SST anomalies on the EASM have achieved great progress. From sub-seasonal, interannual to interdecadal timescales, this paper has briefly reviewed the advances in the studies on impacts of the tropical air-sea interactions on the EASM and the associated mechanisms, with focuses on the main progress of the impacts of El Ni?o–Southern Oscillation (ENSO), tropical Indian Ocean and Atlantic. In addition, roles of tropical SSTs in the link between EASM and the East Asian Winter monsoon are also systematically reviewed. Finally, we put forward several related issues that need to be further investigated in the future, for instance, the impact of tropical SST anomalies on the sub-seasonal variation of EASM, tropical SST changes under global warming and its impact on the EASM.
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Available online:November 08, 2023 DOI: 10.3878/j.issn.1006-9895.2310.23303
Abstract:This study reviews the seasonality and temporal-spatial scale dependence of the air-sea relationship based on recent analyses of the relationship between surface turbulent heat flux and sea surface temperature. The contents include the representation, regional change, seasonal change and temporal and spatial scale variation of surface turbulent heat flux-sea surface temperature relationship as well as relative contributions of surface wind speed and sea-air humidity difference to changes in surface latent heat flux-sea surface temperature relationship. The surface turbulent heat flux-sea surface temperature relationship displays notable differences between the mid-latitude oceanic frontal zones and subtropical gyre regions. In the mid-latitude oceanic frontal zones, the oceanic process has a main contribution to sea surface temperature variations, indicative of an oceanic forcing, which is stronger in winter than in summer. In the subtropical gyre regions, surface turbulent heat flux plays a major role in sea surface temperature variations, indicative of an atmospheric forcing, which is more obvious in summer than in winter. In the western Arabian Sea, the oceanic process has an obvious influence on sea surface temperature variations in summer, indicative of an oceanic forcing, whereas the surface turbulent heat flux has a major influence in winter, indicative of an atmospheric forcing. In the Bay of Bengal, the South China Sea and the Philippine Sea, the atmospheric forcing is prominent in both winter and summer. In the mid-latitude ocean frontal zones during winter and the western Arabian Sea during summer, the oceanic forcing increases with the time scale, whereas in the other regions and seasons, there exists a transition from the atmospheric forcing in shorter time scales to the oceanic forcing in longer time scales with the transition time scale of about 20-40 days. In the mid-latitude oceanic frontal zones, the oceanic forcing decreases with the increase of the spatial scale and switches to the atmospheric forcing with the transition spatial scale shorter in summer than in winter. The atmospheric forcing usually enhances with the increase of the spatial scale.
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Available online:November 08, 2023 DOI: 10.3878/j.issn.1006-9895.2310.23301
Abstract:In recent years, the frequency and intensity of extreme climate keep increasing significantly, particularly in China (Yin et al., 2023b), which poses more and more threats to the social-economic and life security. Chinese scientists are also paying more and more attention to the extreme climate in China and East Asia. In contrast, although the middle and high latitudes of Asia are also highly sensitive to climate change, they have received relatively little attention, which may be due to the relative lack of climatic data, or may be related to the low population and economic and social development in the high latitudes of Asia (especially Siberia). In fact, with the deepening of the research on the amplification effect of the Arctic warming, it is extremely necessary to carry out the research on the impact of climate change and extreme climate in the middle and high latitudes of Asia, and extend our research concern from East Asia to the north. There are many key scientific issues to be investigated, especially the processes, mechanisms and predictability of climate extremes in the region, their impact on ecosystems, and their future evolution. Therefore, the Geoscience Division of the National Natural Science Foundation of China supported this research as a major project on a merit-based selection (the project implementation period is 2020-2024). In this paper, the author briefly introduced the framework of the project and some preliminary research progresses.
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Yang Ruyi, Zhang Yuanchun, Sun Jianhua, Mu Jianli, Yu Tingzhao
Available online:November 08, 2023 DOI: 10.3878/j.issn.1006-9895.2309.23080
Abstract:A typical mesoscale convective system (MCS) over the second-step terrain that moved eastward, merged with convection moving eastward from the eastern edge of the Tibetan Plateau (TP), and influenced the downstream convection systems, had been studied using a numerical simulation. The case occurred from June 29 to July 1, 2016, and resulted in heavy precipitation in the middle reaches of the Yangtze River to the Yangtze-Huai River Basin. This simulation had successfully reproduced the eastward movement of the MCSs over the second-step terrain and the merging with convection moving eastward from the TP, which affected the downstream convective systems. The results revealed the spatiotemporal distribution of precipitation over the middle and lower Yangtze River. The evolution of the MCS is divided into four stages: the formation stage, the propagation stage, the merging stage, and the weakening stage. Due to the cyclonic disturbance in the northeastern part of the Southwest Vortex, the MCS formed in the western mountainous area over the second-step terrain. After moving eastward out of the second-step terrain, the MCS merged with the eastward-propagating convection from the eastern edge of the TP over the downstream areas, which promoted the strong development of upward motion, enhanced the convergence in the lower layers, and induced a mesoscale vortex in the lower troposphere. The mesoscale vortex and the merged convection gradually coupled, triggering heavy rainfall in the eastern plains east of the second-step terrain.
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Available online:November 08, 2023 DOI: 10.3878/j.issn.1006-9895.2309.22231
Abstract:Abstract Based on FY-2G geostationary meteorological satellite and precipitation data, the spatiotemporal distribution characteristics and their relationship of convective clouds and heavy rainfall in mountainous areas of southwestern Sichuan were analyzed under the influence of the western Sichuan Plateau at the eastern side of the Qinghai-Tibetan Plateau from June to September during 2019-2021. The results show that: (1) The Ganzi Prefecture (98～103°E, 28～32°N) of the western Sichuan Plateau in the southeast part of the Qinghai-Tibetan Plateau is an active center of convection, and convective clouds mainly move southwards following the northwest path from the western Sichuan Plateau. After arriving at the Panxi region of mountainous areas of southwestern Sichuan, convective clouds keep moving in three directions: eastward, southeastward, and southward, respectively. And these pathways areas are also the key formation areas of heavy precipitation in mountainous areas of southwestern Sichuan. (2) Heavy rainfall related to the northwest path influence in mountainous areas of southwestern Sichuan is more significant in June-July than in August-September, with the most in July and the least in September. Moreover, the frequency of heavy precipitation for the southeastward-moving type is the highest, followed by the southward-moving type, and the eastward-moving type is the least, exhibiting prominent inter-monthly variation. (3) In the key area of the western Sichuan Plateau, because of the typical north-south ridges of Hengduan Mountains, the Shaluli Mountains and Great Snow Mountains form the generation area of the initial convection for heavy precipitation under the northwest path influence at 14:00~15:00 Beijing time, while the characteristics of their initial convection, the influencing time and the precipitation peak differ from each other for the eastward-, southward- and southeastward-moving convections. (4) The hourly short-duration heavy precipitation under the northwest path influence has obvious characteristics such as single peak and night rain, while the abruptness, duration and intensity of heavy precipitation for the eastward-, southeastward-, and southward-moving convections exhibit certain differences. (5) Although the initial convection and the convective clouds that first affect heavy precipitation along the northwest path in mountainous areas of southwestern Sichuan both originate from the key area of the western Sichuan Plateau, these features such as the convective location, development impact, precipitation distribution and precipitation center are disparate depending to the next eastward-, southeastward-, and southward-moving types. In a word, it is of important significance for further understanding the meso- and micro-scale convective activities and its influence on heavy precipitation in complex mountainous areas under the topography of the Qinghai-Tibetan Plateau.
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Available online:October 27, 2023 DOI: 10.3878/j.issn.1006-9895.2308.23058
Abstract:Based on the Normalized Differential Vegetation Index (NDVI) dataset obtained from the Advanced Very High Resolution Radiometer (AVHRR) of the National Oceanic and Atmospheric Administration (NOAA), as well as the high-resolution near-surface air temperature and surface precipitation rate of China meteorological forcing dataset (CMFD) from 1982 to 2018, the variation characteristics of vegetation and their response to climate warming and humidification in Qinghai Plateau during the growing season (May-September) were studied. The methods used in this study include linear tendency estimation, M-K test, partial correlation and analysis of variance, etc. The results show that: (1) During the growing season of Qinghai Plateau from 1982 to 2018, the vegetation exhibits a spatial distribution feature that decreases gradually from southeast to northwest, and there is a significant increasing trend overall with a climate tendency rate of 0.01/10a. However, the trend of vegetation has a bi-polar development feature in space, that is to say, while the vegetation in the eastern and southwestern parts of the Qinghai Plateau improves significantly (57.3% of the total area), the vegetation of the Qaidam Basin in the northwestern part of the Qinghai Plateau shows a deterioration trend (14.8% of the total area). (2) During 1982-2018, the climate of the Qinghai Plateau is characterized by warming and humidification as a whole, but there are differences in the regions and intensities of climate warming and humidification in different periods. The warming in P1 period (1982-1998) was stronger than that in P2 period (1998-2018), and the humidification in P2 period was stronger than that in P1 period. The trend of NDVI in the growing season of Qinghai Plateau shows a significant mutation around 1998. Before 1998, it fluctuates with no obvious trend, but after 1998, it shows a significant increasing trend, which is consistent with the warming and wetting trend of the Qinghai Plateau vegetation. (3) There is an interdecadal variation in the response of surface vegetation on the Qinghai Plateau to climate warming and humidification. In P1 period, the heat factor (air temperature) inhibits the growth of surface vegetation under insufficient water conditions, while in P2 period, under relatively sufficient water conditions, both water and heat factor promote the growth of surface vegetation. Therefore, the surface vegetation of Qinghai Plateau vastly improves in the growing season.
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Chen Hongbin, Shi Hongrong, Fan Xuehua, Xia Xiang''ao
Available online:October 26, 2023 DOI: 10.3878/j.issn.1006-9895.2309.23320
Abstract:Long-term observations of aerosol optical properties are critical for quantifying aerosol radiative forcing and climate effects, as well as for studying air quality and environmental health. This paper provides a systematic review of the global AERONET network and introduces the development and research achievements of the AEROENT Beijing station, which has the longest observation time in China. Based on more than twenty years of observation data from the Beijing station, the multi-time scale variability of optical radiation products is analyzed. The importance and urgency of long-term observations are also discussed.
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Available online:October 26, 2023 DOI: 10.3878/j.issn.1006-9895.2309.23306
Abstract:Tibetan Plateau (TP) snow anomalies (TPSA) in winter-spring is one of the important predictors of the East Asian summer monsoon (EASM). This paper systematically reviews the studies on the impacts of the interdecadal transition of TPSA on the EASM in recent 20 years. The main conclusions are as follows: (1) interannual variability of the TPSA shows a striking shift from an east-west dipole to a mono-sign structure, which was affected by the sea surface temperature anomalies in the North Pacific and tropical Atlantic, and also bound up with the Antarctic Oscillation and Arctic Oscillation. (2) The interdecadal change of the TPSA in spring influences the EASM precipitation by impacting the subtropical westerly jet in the upper troposphere and the low-level moisture transport. (3) The TPSA can impact the Meiyu rain belt through the “TP atmospheric river” mechanism. (4) The Atlantic Muti-decadal Oscillation can modulate the relationship between the spring TPSA and the Meiyu precipitation. This relationship is robust (weak) during the positive (negative) phase of the Atlantic Muti-decadal Oscillation. Finally, this paper discusses the and prospects the key scientific issues in the influence of the TPSA on the EASM.
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Available online:October 26, 2023 DOI: 10.3878/j.issn.1006-9895.2305.23314
Abstract:The CNMM-DNDC, which is developed by the authors, is a three-dimension (3D), high-resolution and process-oriented terrestrial hydro-biogeochemical model that fully couples the cycling processes of carbon (C), nitrogen (N), phosphorous (P) and water in terrestrial ecosystems at site, catchment, regional, or global scales. Here, this model is reviewed in terms of development background, basic ideals and theories, core scientific processes, characteristics and features, comprehensive functions, verification by observations, and preliminary applications at site, regional or catchment/basin scales. Since the publication of its first version in 2018, this model has undergone several scientific process improvements and function enhancements. As a result, the cycles of C, N, P elements and water have been fully coupled in this model through numerically linking a series of biogeochemical reactions of these life elements, and matter phase changes and mechanical movements, which are occurring in terrestrial earth surface systems. Wide validations with field comprehensive observations demonstrate that the CNMM-DNDC model can be generally applicable for long time 3D and “3H” integrative simulations of terrestrial ecosystems in different bioclimatic zones from tropical to boreal permafrost regions, wherein the “3H” is referred to high spatial, high temporal and high process resolutions. As this model is designed to well describe the biogeochemical transformations and the 3D movements of the three life elements and water at different (site, ecosystem, catchment/basin, regional or global) scales, available validations and preliminary applications so far have demonstrated its potential to simultaneously predict multiple variables to measure the sustainability in terms of the United Nations Sustainable Goals (SDGs). The predictable variables include at least hydraulic soil erosion, surface runoff and subsurface flow, leaching of water and C, N and P solutes, horizontal flows of dissolved and particle C, N and P substrates or matter, emissions of greenhouse gases (carbon dioxide, methane, and nitrous oxide) and gaseous N pollutants (ammonia and nitric oxide), ecosystem productivity, water evapotranspiration, and balances of energy, water, C, N and P. The CNMM-DNDC model is expected to provide advanced technical support of numerical simulation for the multiple-goal implementations of the SDGs, as it could be a) a robust tool for virtually experimental studies on complex processes at different scales and b) a core model of a decision supporting system to optimize carbon and environmental management.
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xuyongfang, liaojie, zhaoyufei
Available online:October 25, 2023 DOI: 10.3878/j.issn.1006-9895.2310.23069
Abstract:Based on the data set of the China"s basic elements of meteorological radiation (V2.0) archived by the National Meteorological Information Centre, a dataset of 1991-2020 China Surface Meteorological Radiation Climate Normals is developed. During the development of the dataset, a systematic quality check and verification revision of the metadata of the ground radiation station observation dataset since 1991 was carried out. Based on the site migration information of the observation station and the radiation observation history documents, the time nodes of manual observation to automatic observation were counted, and the segmentation information needed for climate statistics was established. A set of radiation climate background fields unified as automatic observation methods with better representation was provided. Based on the hourly radiation data of the China"s basic elements of meteorological radiation (V2.0), the hourly annual climate normal of China"s surface meteorological radiation is obtained. Compared with the hourly radiation climate value of China"s surface meteorological radiation from 1981 to 2010, it provides a higher temporal resolution of the radiation climate value statistics, and has a wider application value. 1991-2020 China Meteorological Radiation Climate Normals provides the climatic background information of the hourly (daily, monthly, annually) total radiation, net total radiation, scattered radiation, vertical direct radiation, horizontal direct radiation and reflected radiation of about 103 stations in China (including the mean value, cumulative value, extreme value and occurrence date), providing data support for weather and climate research.
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Danyun Wang, Xiaodong Zeng, Xiang Song
Available online:October 20, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22067
Abstract:Evaluation of climate and vegetation status in earth system models (ESMs) is fundamental to understanding climate change, terrestrial ecosystems, and the carbon cycle. In this study, the temperature, precipitation, and LAI in the growing season over China from eighteen ESMs of the Sixth International Coupled Model Comparison Project (CMIP6) were evaluated based on site observation and remote sensing data. Then, a multiple linear regression model was used to quantify the sensitivity of LAI to temperature and precipitation, and to evaluate the ability of the CMIP6 model to simulate the sensitivity of vegetation in geographical and climatic spaces. At last, the models with a better simulation performance were selected. The results show that (1) Most models can simulate the spatial distribution of temperature, precipitation, and LAI in the growing season, but there are obvious deviations in their mean value and change trends. (2) Compared with the observation, The simulation ability of LAI sensitivity to temperature and precipitation showed that the simulation of the positive region was better than the negative region, and the sensitivity of vegetation in ecotone was greater than that in China. There was a large deviation in the amplitude of vegetation sensitivity and its distribution in climate space (i.e., the corresponding relationship with climate field). (3) Comprehensively based on evaluations above, CANESM5-CanOE, INM-CM5-0, IPSL-CM6-LR, and MPI-ESM1-2-LR have the best performance on simulations of climate and vegetation during the growing season in China.
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XIE Yue, RAN Lingkun, SHEN Xinyong, HUANG Wei, and ZHOU Kuo
Available online:October 16, 2023 DOI: 10.3878/j.issn.1006-9895.2211.22220
Abstract:The heavy rainstorm that occurred on September 9–10 on the southern slope of the Tianshan Mountains was numerically simulated using Weather Research Forecast (WRF) model with European Meteorological Center ERA5 0.25°×0.25° reanalysis data and precipitation data from the CMORPH satellite. The potential instability feature was analyzed, and the influence of different scales of topography perturbations on the variation of potential instability was examined using the topographic sensitivity test and the terrain-following tendency equation of potential stability. The following results were obtained: (1) The lower atmosphere was potentially unstable before the rainfall. However, with the release of unstable energy, the lower atmosphere tended to become stable after the rainfall. (2) the potential divergence term caused by flow-over wind mainly was the primary forcing term in the tendency equation of potential stability. The dominant term of flow-over potential divergence was the vertical shear of meridional flow-over wind coupled with the meridional gradient of generalized potential temperature term. During the rainstorm, the development of potential instability was affected by the vertical shear of meridional flow-over wind and meridional gradient of generalized potential temperature, which were changed by topography perturbations. This ultimately led to the occurrence of the rainstorm. The findings of this study could be helpful in improving the forecast of rainstorms in Xin Jiang.
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Yin Lei, Wang Jin, Tang Xiba, Li Na
Available online:October 10, 2023 DOI: doi:10.3878/j.issn.1006-9895.2306.23047
Abstract:In this study, a hailstorm that occurred in Guiyang, Guizhou province on 19 May 2020 was numerically simulated using the Weather Research and Forecasting (WRF) model version 4.2. It was revealed that the numerical simulation generally reproduced the moving path of the hailstorm in Guiyang. By analyzing the dynamic, thermodynamic and microphysical structure of the hailstorm during the different developing stages and diagnosing the tendencies of hail mixing ratio, the microphysical mechanism of hail formation was studied, and a conceptual model was given. The main conclusions were as follows: (1) The simulated hailstorm in the mature stage was characterized by a super-cell storm, existing free-echo and overhang region. The updrafts reached up to 12 km with a maximum vertical velocity of about 20 m s-1, and then flow out eastward as a result of the westerly wind in the upper troposphere, forming wide anvil clouds. Strong downdrafts existed at lower levels in the rear of the updraft region. (2) Hail embryos were formed through the collection of raindrops by cloud ice (Piacr), occurring at 6-7 km, and then grew up by collecting supercooled cloud droplets and raindrops (Psacwg, Pracg). The main sink term of hail was melting to rain (Pgmlt). (3) During the mature stage of the hailstorm, Psacwg, which mainly happened at upper levels of the strong updrafts (6-10 km), increased significantly and produced large mass content of hail with a maximum value of 11 g kg-1 in the region of overhang echo and the upper levels of updrafts. (4) During the dissipating stage of the hailstorm, the vertical velocity decreased and the anvil clouds in upper troposphere expanded. The net production rate of hail decreased and led to a reduction of hail mixing ratio, while the conversion rate of Pgmlt increased, and produced large amount of rain water near the ground.
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Available online:October 10, 2023 DOI: 10.3878/j.issn.1006-9895.2306.23055
Abstract:The changing climate has increased the frequency of hazardous weather events, which has placed higher demands on monitoring hazardous weather. In addition to the conventional S-band and C-band operational radar networks, in recent years, many cities in China have built X-band weather radar monitoring networks to improve the spatiotemporal resolution of hazardous weather monitoring and the low-level observation information of weather systems. Hybrid-tilt reflectivity is extracted from the multi-tilt radar measurements over the radar domain, which is closest to the surface and not affected by orographic blockage. It is important for monitoring the occurrence and development of convective systems. In order to take advantages of the wide detection range of S-band or C-band weather radars and the high spatiotemporal resolution of X-band weather radars, this study presents a method of mosaicking hybrid-tilt radar reflectivities derived from the measurements of S-band or C-band and X-band weather radars. This method includes 1) generation of hybrid-tilt reflectivity, 2) conversion of radar reflectivity in different frequencies, and 3) mosaicking of reflectivity measurements from multiple radars. Based on this method, the hybrid-tilt reflectivity mosaic products of Shenzhen and Xi’an are generated, with the spatial resolution of 30 m and the temporal resolution of 1 min. During the events of different precipitation types, the hybrid-tilt reflectivity mosaic products are evaluated using the reflectivity measurements from the Dual-frequency Precipitation Radar onboard the Global Precipitation Measurement Core Observatory (GPM-DPR). The result shows that the hybrid-tilt reflectivity mosaic products are highly consistent with the GPM-DPR reflectivity measurements, and the mean errors are within ±1dB.
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Available online:October 10, 2023 DOI: 10.3878/j.issn.1006-9895.2307.23311
Abstract:We have reviewed recent researches associated with the Atlantic Multidecadal Oscillation (AMO) and its influences on East Asian climate. Specifically, we focus on the drivers, index definitions, impacts on East Asian summer and winter climates of the AMO as well as the combined effects of the AMO and other Oceans. Until now, the mechanisms of the AMO are still under debate. The AMO is considered to be caused by the multidecadal Atlantic Meridional Overturning Circulation (AMOC) variability, the external forcings (e.g., aerosols) or the stochastic atmospheric forcing. The positive phase of the AMO can strengthen the East Asian summer monsoon and increase the summer precipitation and temperature over East Asia through three ways, and vice versa. Meanwhile, under the positive AMO phase, the East Asian winter monsoon system is strong and the mid-latitude Eurasian continent and northern China are cold, and vice versa. Given the importance of AMO, further understanding the drivers of AMO and its climatic impacts on East Asian climate is conducive to improving decadal to interdecadal predictions of East Asian climate.
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Song Linye, Yang Lu, Cheng Conglan, Chen Mingxuan, Cao Weihua, Wu Jiankun
Available online:October 07, 2023 DOI: 10.3878/j.issn.1006-9895.2306.23059
Abstract:Based on the high resolution integrated forecast system of RISE, using the meso-scale CMA-BJ model with 3km resolution and the global-scale ECMWF model with 0.125 degree resolution, adopting the hourly observation data of conventional and dense automatic weather stations, taking the outdoor mountainous competition area in Beijing Winter Olympics as the research area, this study compares the effects of different numerical weather prediction (NWP) model background on the accuracy of surface 2-m temperature and 10-m wind analysis and hourly forecast for the future 1-24h with 100m grid resolution. The results show that: (1) Both the regional and global models can be used as the background of RISE system to effectively form 100-meter fine integrated products in complex terrain, but the impacts of different NWP model backgrounds on the analysis and forecast performance for different meteorological elements are obviously different; (2) For temperature analysis, the model background has the least influence. The spatial distribution of RISE temperature analysis with CAM-BJ and ECMWF as the NWP model background is basically the same, and the MAE error is both less than 0.2oC; (3) For wind analysis, adopting high-resolution regional model can improve the refinement level of RISE high-precision wind integrated products better than the global model with coarse resolution; (4) For temperature forecast, the performance of RISE 100m grid forecasts with ECMWF model background is significantly better than that with CMA-BJ model background, and the average forecast errors for Winter Olympic alpine stations and all stations are reduced by 10.5% and 7.0%, respectively. (5) For wind speed forecast, the MAE errors of 1-6h forecast for RISE Winter Olympics alpine stations with CAM-BJ and ECMWF model backgrounds are 1.42m/s and 1.30m/s, respectively, and the MAE errors of 7-24h forecast are 1.52m/s and 1.54m/s, respectively. Besides, the average 1-24h MAE errors for all stations in RISE region are 1.38m/s and 1.24m/s, respectively. The results in this study are helpful to further understand the role of model background in the 100-meter-level integrated forecast, and have important scientific significance and practical value for improving the accuracy of weather forecast in complex terrain.
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Meng TIAN, Bingui WU, Yunchen LIAO, Jianbo YANG, Hailing LIU
Available online:September 15, 2023 DOI: 10.3878/j.issn.1006-9895.2307.22249
Abstract:Radiative cooling at the top of fog is a crucial physical process during the evolution of fog, driving a “top-down” turbulent mixing. Therefore, the YSU (Yonsei University) scheme incorporates a module (ysu_topdown_pblmix) to represent this process. However, the influence of such “top-down” turbulent mixing on heavy fog events in the North China Plain remains unclear. This study evaluates the suitability of ysu_topdown_pblmix in simulating fog events in the North China Plain based on Himawari-8 satellite retrievals, automatic station observations, 15-layer atmospheric boundary layer gradient measurements, and 5-layer turbulence-related observations. Large-eddy simulations are also used to supplement the analysis. The investigation reveals that while ysu_topdown_pblmix overall decreases the fog area simulation scores in the North China Plain, it significantly improves the simulation of near-surface temperature, humidity, and fog boundary layer structure. This enhancement is attributed to the “top-down” turbulent mixing driven by radiative cooling at the fog top. However, the present ysu_topdown_pblmix exhibits an excessive entrainment effect, leading to too much intrusion of warm air above the fog top, resulting in rapid dissipation of fog. Sensitivity tests demonstrate that reducing the evaporative enhancement coefficient in ysu_topdown_pblmix can mitigate the strength of turbulent entrainment at the fog top, thereby improving the simulation of fog events. These findings suggest that incorporating ysu_topdown_pblmix is necessary for numerical simulations of heavy fog events in the North China Plain, but further refinement of relevant parameters is required.
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Li Yanhui, Zhang Feimin, Yang Kai, Wang Chenghai
Available online:September 13, 2023 DOI: 10.3878/j.issn.1006-9895.2303.22201
Abstract:In this paper, wind profile radar, runway automatic observation and Doppler weather radar were used to analyze the occurrence and evolution characteristics of a dry downburst (referred to as "5.14" in this paper) under a weak synoptic scale forcing in the semi-arid region of Lanzhou on May 14, 2020. The mesoscale numerical model WRF (Weather Research and Forecasting) is used to simulate the formation, movement and evolution characteristics of the hydrocondensate over the divergence outflow area of the process, and the possible mechanism of the outflow propagation of the process 5.14 is discussed. The results show that the lifetime of "5.14" process is about 30 min, and the cloud top height is more than 9 km. At the height of 3-6 km to the rear of the cloud body, the sudden intrusion of dry cold air jet, the fracture of cloud body, the collapse of cloud top, the downward transmission of momentum and the divergence of outflow jet at the height of 1-4 km in the middle and low altitude are the possible causes of the outflow of downburst. Snow crystals collide with supercooled cloud droplets to freeze and merge, resulting in a rapid growth of graupel particles in both sinking and outflow areas. The simulated mixing of graupel particles is 105 times larger than that during the outbreak of downburst. Graupel particles in sinking zone accelerate the formation of cold pools in clouds, which is one of the reasons for the excitation of strong downdraft. With the movement of the cloud body, the strong downdraft generates divergence outflow on the ground, and the intersection of the adjacent divergence outflow leads to the convergence upward movement of the airflow. Two updraft areas are formed on both sides of the downdraft at the front of the cloud body movement direction. With the deepening of the cold and dry inflow jet, two vertical circulations are generated in the direction of cloud body movement. The vertical circulation is formed by an updraft and a wet downdraft in the cloud. The wet downdraft in the vertical circulation forms cold pool diffusion near the surface, which promotes the burst of downburst and stimulates the gust front. The gust front diffused in the outflow direction of the downward-hitting storm divergence center, and the warm and wet updrafts in front of the gust front helped the new units merge into the original storm, and the storm was strengthened. With the advance of the gust front, the warm and wet updrafts were cut off, leading to the sinking of the heavy cold cloud top, and the continuous upward-rushing and collapsing of the cloud top formed the outflow propagation process of the downward-hitting storm. Rainwater particles transported by updraft in front of gust front are frozen near the 0 ℃ temperature layer. Heat released in the freezing process leads to the continuous rise of 0 ℃ temperature layer in the process of outflow propagation, and the melting layer of graupel particles sinking in the clouds rises. The evaporation layer of rainwater particles formed after melting increases in the falling process. As graupel particles melt and rainwater evaporates and absorbs heat in the process of falling, cold pools near the ground are constantly strengthened, leading to increased surface wind speed in the process of divergence propagation, which is an important reason for the formation of surface gales in the outflow propagation of downburst. The updraft, on the other hand, heats the atmosphere by condensation and enhances the upward motion. The development of downdraft contributes to the formation and maintenance of convective circulation and cold pool. After the formation of the downburst, the vertical closed circulation formed continuously in the direction of cloud body movement is the moving mechanism of the divergence center of the downburst. Due to the convergence and uplift effect of the outflow of the surface cold pool, the range of the updraft zone in the moving direction keeps increasing, and the vertical closed circulation cannot be regenerated due to the blockage of the updraft zone. At the same time, the eastward movement of the cloud body maintains the weakening of the circulation of water condensate in the vertical closed circulation structure of the downburst, which dissipates the vertical closed circulation structure and leads to the weakening and extinction of the divergence center of the downburst. Compared with previous studies, this dry downburst also has such features as inflow jet at the back of cloud body, radar echo reflectivity factor nuclear decline, momentum downflow, high water content of graupel particles, heat absorption and cold pool formation in the melting and evaporation process of water condensate. However, there is an obvious vertical closed circulation in the divergence center of dry downburst, which is the starting and maintaining mechanism of the divergence center of downburst. At the same time, the divergence center of downburst is closely related to the formation of gust front, and the gust front process is the main reason for the outflow propagation of dry downburst to form surface gales.
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Lu Chuanbin, Dai Qiudan, 陈娟, 孙向明, 张思超
Available online:September 08, 2023 DOI: 10.3878/j.issn.1006-9895.2308.23091
Abstract:As a city with large population and food supply, Fuyang’s rapid urbanization process in recent decades has caused urgent attention to its climate and environmental issues. Research on the long-term boundary layer structure and its relationship with meteorological conditions in the context of climate change is of significant importance. By using conventional meteorological observation data from Fuyang, Anhui Province, high-resolution L-band sounding observations from Fuyang sounding station between 2010 and 2019, as well as the ERA5 reanalysis data, we employed the bulk Richardson number method to calculate the planetary boundary layer height (PBLH). The characteristics of the long-term PBLH variations in the Fuyang region were compared and analyzed. The relationships between PBLH and meteorological factors such as 10-m wind speed, near-surface temperature, relative humidity and surface pressure were analyzed at monthly, seasonal, and interannual scales using multi-year data. The discrepancies between the observed PBLH and those from the ERA5 were also examined. The results indicate that the PBLH observed at 08:00 and 20:00 throughout the year in Fuyang remained below 500 m. This was due to the relatively weak solar radiation during these time periods, leading to under-developed boundary layer or transitioning towards nocturnal stable boundary layer conditions. The PBLH at 20:00 was higher than at 08:00, which is attributed to the combined effects of lower pressure, higher temperature, and lower relative humidity in the evening, which led to a higher uplifting of the PBLH and surpassed the effect caused by lower wind speeds. The PBLH exhibited significant seasonal variations regardless of the observation time (8:00 or 20:00), with the order of seasons being summer > spring > winter > autumn. The ERA5-derived PBLH exhibited a generally consistent seasonal variation pattern with the observations. The ERA5 PBLH was 23 m higher than the observed PBLH at 08:00, primarily due to elevated wind speeds, higher temperatures, and lower atmospheric pressure in ERA5. However, at 20:00, the ERA5 PBLH was 99 m lower than the observed PBLH with more complex influencing factors. The multi-year monthly averaged correlation coefficients between ERA5 and observed PBLH were relatively high, with values of 0.91 and 0.74 at 08:00 and 20:00, respectively, indicating the potential of using ERA5 data for long-term trend studies of PBLH in Fuyang and southeastern regions. The fluctuation patterns of observed and ERA5 annual average PBLH showed overall consistency over the years, but there is stable in the data of observed PBLH, while in ERA5, a slightly decreasing trend is demonstrated (not statistically significant at p<0.05). At the monthly average scale, surface meteorological factors significantly influenced PBLH, with atmospheric pressure and wind speed exerting a greater impact compared to temperature and humidity. The multi-year monthly averaged PBLH from ERA5 exhibited a significant negative correlation with surface pressure and a strong positive correlation with surface wind speed. The correlation was stronger at 08:00 compared to 20:00; The relationship between the annual average PBLH value and the ground meteorological elements is not significant, therefore, although climate change leads to an increase in surface temperature and relative humidity, the change of annual average PBLH is statistically not significant. Intensive observations indicated that both observed and ERA5-derived PBLH gradually increased from 02:00 to 20:00, followed by a decrease, reflecting the typical diurnal variation characteristics of boundary layer height, with a deeper boundary layer during the day and a shallower boundary layer at night.
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Available online:September 06, 2023 DOI: 10.3878/j.issn.1006-9895.2307.23022
Abstract:The southwest vortex (SWV) has strong disasterability and extensive influence, which is of great significance to reveal its rainfall mechanism and climate characteristics. The objective identification algorithm based on grid data is one of the important basic contents in the research field of the SWV. The local disturbance caused by high spatial resolution grid data and the influence of topography on the integrity of SWV circulation are the main reasons for the low identification accuracy of existing algorithms. In this paper, a new objective identification method for the SWV based on 700hPa wind field is proposed. This method can overcome the adverse effects of local disturbance and terrain occlusion without pre-processing the identification data such as smoothing, and significantly improve the accuracy of the SWV center identification. The improved tracking algorithm can recognize the new SWV, avoid the wrong connection of the old and new SWV centers, and obtain more objective SWV tracks. The evaluation results show that the average identification hit rate, missing report rate and false alarm rate of the new method are 85.71%, 14.29% and 11.7%, respectively. In the area east of 104°E, which is less affected by terrain, the identification hit rate is more than 90%, and the missing report and false alarm rate are both lower than 10%. Better recognition effect and higher computational efficiency make the new method more satisfying to the needs of scientific research and professional work.
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LIU Huijun, WU Qishu, WEI Guofei, HAN Mei, PAN Ning
Available online:September 06, 2023 DOI: 10.3878/j.issn.1006-9895.2307.2115
Abstract:Taking the correction experiment of ECMWF model station forecast of 12 h cumulative precipitation as an example, taking Fujian, Jiangxi, Zhejiang and Shanghai as the research area, three technologies cited or initiated by Fujian when realizing the optimal threat score (OTS) correction method are introduced in detail, and compared with similar technologies. The results are summarized in the following points: 1) The 3-year quasi-symmetric sliding window sampling method is used to collect training samples to calculate the OTS correction threshold, and the effect is better than that of the sampling method of collecting the samples from the same season in the previous 3 years. 2) The magnitude of the OTS correction threshold F1 (i.e. elimination threshold) is closely related to the magnitude of 2 m temperature. As the temperature rises, the elimination threshold first increases and then decreases. Compared with the modeling scheme without grouping, the grouping modeling based on the maximum 2 m temperature forecast can obtain the elimination threshold under different temperature conditions, which can simultaneously reduce the false alarm ratio and missing ratio of light rain, and improve the equitable threat score of light rain by 5.0%~8.2%. 3) The effect of the first scheme, which is to use the inverse distance weighted interpolation method to interpolate the model precipitation forecast, and then use the OTS correction method to correct the precipitation forecast, is better than that of the second scheme, which is to use the nearest neighbor interpolation method to interpolate the model precipitation forecast, and then use the OTS correction method to correct the precipitation forecast.
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Available online:August 31, 2023 DOI: 10.3878/j.issn.1006-9895.2306.23063
Abstract:A transitional snow event occurred in Fujian Province on 19 to 23 February 2022 and was characterized by the co-existence of warm layer in the middle troposphere and cold layer in the lower troposphere. Multiple precipitation types occurred on the ground including rain, snow and wet snow, etc., increasing the difficulty of forecasting. Based on data from weather radars and other sources, , a classification method of precipitation types is firstly used to identify the time periods of snow and wet snow at each weather station, on this basis, the influence of environmental temperature evolution on transitional snow event as well as the vertical characteristics of transitional snow event are investigated by analyzing synoptic circulation and vertical features of radar variables. The results show: (1) the transition between snow and wet snow could be clearly distinguished according to the characteristics of VPR and environmental temperature information in areas that topography and surface temperature are uniformly distributed, that is, VPR monotonously increases with decreasing height during snow stage, while a significant bright band presents in the middle layer of VPR during wet snow stage. Great emphasis should be put on the capability of weather radars in observing precipitation in the lower level. If radar variables could not capture the change of precipitation characteristics caused by the difference of temperature in the near-surface layer due to the limitation of observation environment, the precipitation types on the ground could be markedly different even though the VPR features resemble each other in higher layer. (2) the vertical characteristics of polarimetric radar variables indicate that, the growth mechanism of hydrometeors in the upper layer and above melting layer is similar to general dry snow events, the major differences of transitional snow events are the complicated melting and refreezing processes of particles caused by the warm layer and cold layer. A bright band signature displays when hydrometeors falling through warm layer, then melted particles are fully or partially frozen reaching the ground as snow or wet snow, depending on the intensity of cold layer beneath warm layer and temperature at surface. The vertical features of radar variables (e.g. the change of intensity of bright band) could timely reflect the change of environmental temperature, which is conductive to distinguish precipitation types and could make up for the inaccurate forecasting of numerical model and the absence of atmospheric profiles to some extent.
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Qi Duo, CUI Xiaopeng, ZOU Qiangli, JIANG Rouyi, GAO Hua
Available online:August 31, 2023 DOI: 10.3878/j.issn.1006-9895.2304.23026
Abstract:Using high-resolution simulation produced by the WRF (weather research and forecasting) model, three dimensional precipitation equation, and definition of precipitation efficiency, an heavy rainfall event occurred in Mianning on 26 June 2020 is studied. The vertical dynamic structure, hydrometeor distribution and various physical processes of precipitation are compared and analyzed. The characteristics related to water substances ( water vapor, rain, snow, hail, graupel, ice and liquid cloud) in complex terrain areas are further revealed.The results indicated that the rainstorm process can be divided into two stages. In the first stage, from 1800 BJT (Beijing time) to 2200 BJT 26 June 2020, The sharp ascending motion in the strong precipitation area promotes the convergence of water vapor and liquid-phase hydrometeors from the weak precipitation area. The abundant liquid-phase hydrometeors collected in the strong precipitation area are converted into heavy rainfall and ice-phase hydrometeors to supply cloud growth. At this time, The strong convective echo with the reflectivity of ＞35 dBZ reached the highest level. In the second stage, from 2300 BJT 26 to 0100 BJT 27 June 2020, the local ascending motion in the strong precipitation area is weakened, which leads to the weakening of the convergence of liquid-phase hydrometeors , but the convergence of water vapor is still strong and the location of maximum ascending motion is descended, which is helpful for the condensation of water vapor and the collision of clouds and raindrops. There are two maximum centers of ascending motion in the vertical direction. The echo intensity shows profile of strong-weak-strong. The ice particles in the upper atmosphere may be as seeds for the lower cloud, which is helpful for the conversion of liquid-phase hydrometeors into heavy rainfall. The precipitation efficiency varies significantly among different rainfall intensity ranges, from 5 % to 70 %. The greater the precipitation efficiency, the stronger the surface precipitation.
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Zhanmei Yang, Jingyong Zhang, 杜振彩
Available online:August 31, 2023 DOI: 10.3878/j.issn.1006-9895.2306.22125
Abstract:Under the background of global warming, floods and droughts occur frequently in summer over northeastern China, leading to severe consequence to human and natural systems. However, the current seasonal prediction of summer precipitation over northeastern China is still low, far from meeting the needs of disaster prevention and reduction. The precipitation during the rainy season over northeastern China is mainly concentrated in midsummer (July and August), and its interannual variability is comparable to that of interdecadal variability. This study focuses on analyzing the predictive role of interannual variability of soil temperature in the interannual variability of midsummer precipitation over northeastern China. This study found a significant negative correlation between the interannual variability of midsummer precipitation over northeastern China and the interannual variability of spring soil temperature over central and eastern Europe, as well as a significant positive correlation with the interannual variability of spring soil temperature over the eastern Qinghai Tibet Plateau and northeastern West Asia. The abnormal soil temperature in the key areas in spring corresponds to the abnormal soil temperature in the downstream region during the midsummer, which leads to abnormal atmospheric circulation in East Asia during the midsummer. The upper level westerly jet is strong and northward, and the western Pacific subtropical high is northward, resulting in enhanced water vapor convergence and upward movement over northeastern China, leading to increased precipitation in the midsummer. A seasonal prediction model for the interannual variability of spring soil temperature over central and eastern Europe, eastern Qinghai Tibet Plateau, and northeastern West Asia was established to predict the interannual variability of summer precipitation over northeastern China. The TCC of the Leave-One-Out Cross-Validation can reach a maximum of 0.64 and hindcast for the period of 2012 -2021 can reach a maximum of 0.78 in the GLDAS-Noah, ERA5, and CRA data sets, indicating that spring soil temperature plays a key role in predicting the interannual component of midsummer precipitation over northeastern China. The research results can provide a scientific basis for improving the prediction of summer precipitation over northeastern China, and can be easily applied to actual prediction.
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Liao Shujie, Wu Qigang, Sun leng, Yao yonghong, Hu yuantao
Available online:August 31, 2023 DOI: 10.3878/j.issn.1006-9895.2306.23051
Abstract:The winter and spring snow depths on the eastern Tibetan Plateau (TP) are characterized by interdecadal variability, with a significantly increased trend approximately before 1990 and a decreased trend after 1990. In this paper, we first analyze trends of winter and spring snow depth over the eastern TP in 1960-1989 and 1990-2014, and its relationships with the trends of temperature, precipitation and other atmospheric circulation conditions. Three sets of outputs from the CESM2 model, including (1) total external radiative forcing, (2) well-mixed greenhouse gas radiative forcing, and (3) anthropogenic aerosol radiative forcing, are then used to assess the respective contributions of radiative forcing and North Atlantic Oscillation (NAO) to the trends of snow depth in the eastern TP during the winter-spring period of 1960-1989 and 1990-2014. Observational analyses indicate that the post-1990 snow reduction was mainly caused by increasing surface air temperature and decreasing snowfall, while spring snow depth was mainly caused by increasing surface air temperature. During 1960-1989, all radiative forcing, greenhouse-gas forcing only, or aerosol forcing only contributed little to increased trends of winter and spring snow depth over the eastern TP. The NAO instead contributed about 49% of increased trends of winter snow depth over the eastern TP, but little of increased trends of spring snow depth over the eastern TP. Comparison of observed and modelled trends in other atmospheric variables suggests that all radiative forcing led to significant warming and reduced snowfall on the eastern TP from 1990-2014, and contributed significantly to the continued reduction in both winter and spring snow depths in the later period, explaining 29% and 82% of the observed winter snow depth reduction in the later period. Both greenhouse gas forcing and aerosol radiative forcing contribute significantly to plateau warming and together contribute to the reduction in snow depth in the eastern TP in winter and spring during 1990-2014. The decreasing trend in the NAO index can explain 22% of the reduction in snow depth in the eastern TP in winter from 1990-2014, but contributes slightly to the reduction in snow depth in spring. With future increases in anthropogenic greenhouse gases and decreases in aerosol emissions, warming in the eastern TP is expected to intensify further and snow depth in this area will continue to decrease.
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Available online:August 31, 2023 DOI: 10.3878/j.issn.1006-9895.2305.23020
Abstract:The daily precipitation ensemble forecasts provided by different numerical models are evaluated by "point-to-point" verifications and spatial verifications. The results show that different numerical models have different forecast capabilities for different aspects of precipitation. Based on technology of the Method for Object-based Diagnostic Evaluation (MODE), an Object-based Superensemble (OBJSUP) model is proposed, which employs the similarities of the spatial structure of precipitation objects in the observation field and forecast field as the weights of the contributing models. It is different from the Gridpoint-based Superensemble (GPSUP) that calculates the weights using traditional "point-to-point" error analysis. Compared with the optimal single model, the multi-model ensemble technologies (including OBJSUP and GPSUP) both effectively improve the short- and medium-term precipitation forecasting skills, and the OBJSUP model generally performs better than the GPSUP model. The main reason is that the OBJSUP model can better improve the prediction of the centroid location of the precipitation object. For an extreme heavy precipitation event occurred in Guangdong Province in the summer of 2018, the comparisons between the forecasts of OBJSUP, GPSUP and the high-resolution regional model COSMO (Consortium for Small Scale Modeling) demonstrate that OBJSUP and GPSUP both under-predict the intensity of extreme heavy precipitation, but the COSMO dynamic downscaling exhibits a certain ability to predict the heavy precipitation occurring in eastern Guangdong.
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Available online:August 29, 2023 DOI: 10.3878/j.issn.1006-9895.2307.23308
Abstract:The South China Sea and surrounding areas (SCSSA) is one of the most sensitive regions with strong sea-land-air interactions. Extreme precipitation over the region has received widespread attentions in recent decades, because its large latent heat can exert substantial impacts on climate variability across the globe, through providing substantial energy and moisture for global atmospheric circulations. Utilizing gauge-based gridded data and a statistically downscaled CMIP6 dataset, we systematically investigate the historical and future spatiotemporal characteristics of maximum 1-day precipitation (RX1day), maximum 5-day precipitation (RX5day), very heavy precipitation days (R20) and very wet days (R95p) over this region. The RX1day, RX5day, R20, and R95p are commonly used to represent heavy rainfall, persistent heavy rainfall, high-frequency heavy rainfall, and accumulated heavy rainfall amount, respectively. Result shows that four indices share an analogous spatial pattern during 1951-2014 at annual and seasonal time scales, with large values appearing over Southeast Asia, the Southern China, and southern part of the Tibetan Plateau. That is, these regions are not only with heavy rainfall, but also manifest sustained and high-frequency heavy precipitation. The four indices show large values over Southeast Asia in four seasons, and depict great (small) values over South Asia, the Tibet Plateau, and East Asia in summer (winter). The projected four indices in the future maintain the historical spatial structures, and the four indices averaged over the whole region exhibit increasing trends during 2015-2100 under the SSP1-2.6 and the SSP5-8.5 scenarios. The percentage changes in the four indices during 2016-2035, 2046-2065, and 2080-2099 under two scenarios with respective to 1995-2014 exhibit slightly decrease in Southeast Asia and East Asia, and increase over South Asia and the Tibetan Plateau. In addition, the physical mechanism associated with extreme precipitation over Southeast Asia has been further explored. The cold sea surface temperature anomalies (SSTAs) over Indian Ocean, warm SSTAs over the tropical North Atlantic, and SSTAs over the tropical Pacific and Atlantic are responsible for southern dry and northern wet, overall wet, and northern dry and southern patterns of extreme precipitation over Southeast Asia, respectively.
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Hu Jinggao, Xie Jincai, Ren Rongcai, Liu Shuai
Available online:August 22, 2023 DOI: 10.3878/j.issn.1006-9895.2306.22216
Abstract:Based on the Modern-Era Retrospective analysis for Research and Applications reanalysis dataset, this study analyzes the classification of stratosphere final warming (FW) that takes both the stratosphere and the lower mesosphere into account. The results show that the seasonal transition of circumpolar zonal wind from westerly to easterly wind also exists in the lower mesosphere, which is similar to that in the stratosphere. In addition, the interannual variability of polar-mean air temperature and circumpolar zonal wind in spring in the lower mesosphere is as strong as that in the stratosphere. Thus it is suggested that FW events still appear in the lower mesosphere. The annual FW onset date at each pressure level is then determined. It is found that the average onset date of FW events varies from April 7th to 27th at different pressure levels with a standard deviation varying from 11.3 to 18.3 days. The latest onset occurs at 1 hPa and the minimum standard deviation occurs at 0.1 hPa. According to the characteristics of the vertical profile of FW onset date, this study classifies the FW events into three types. That is simultaneous type, successive type, and climatology-like type, respectively. The FW occurs almost simultaneously at the whole levels from the mid-stratosphere to lower mesosphere in the simultaneous type. Accompanying with the FW occurrence, there is a reversal of the sign of polar-mean geopotential height and temperature anomalies. Strong planetary wave activities dominate the onset process of this type. Although the onset process of the successive type is relatively similar to that of the simultaneous type, the planetary wave activities weaken greatly during the FW onset in this type. The non-adiabatic heating of solar radiation plays an important role in this type. In the climatology-like type, the occurrence of FW event at 10 hPa is dominated by dynamics. After the occurrence of FW event in the mid-stratosphere, the planetary wave activities are inhibited in the upper stratosphere which causes the occurrence of FW event mainly resulting from non-adiabatic heating in those pressure levels. There are two possible explanations for the FW onset at 0.1 hPa. On the one hand, the 0.1-hPa FW onset may be dominated by non-adiabatic heating. On the other hand, for some FW events, secondary planetary wave activities following FW onset in the stratosphere may lead to the onset of FW at 0.1 hPa.
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JIA Jia, DAN Li, WANG Lizhi, Zhan Siyu, Ma Zhuguo
Available online:August 09, 2023 DOI: 10.3878/j.issn.1006-9895.2305.23067
Abstract:The improvement of numerical weather prediction depends on the improvement of the model physical process, the model initial field and model spatial resolution. The improvement of the model resolution has become an effective way to improve the model prediction effect. Based on the global forecast system, T1534 (13km) and T254 (55km) models with different resolutions were used to forecast the temperature, pressure, wind speed and precipitation over China. The results show that, among the two resolution models, North China has the best forecast effect. The correlation coefficients with ERA5 reanalysis data are all above 0.8, and the root-mean-square errors of the seven subregions decrease significantly with the increase of resolution. In the simulation of air temperature, the root-mean-square error in southwest China is 2.171, which is reduced by 30.1% to 1.523 after the model resolution is improved. In the simulation of wind speed, the correlation coefficients of the two resolution products are generally higher in the monsoon region than in the non-monsoon region. In a region with complex terrain, such as northwest China, the root-mean-square error of wind speed increases slightly with the increase of model resolution. It can be seen that the improvement of model resolution may not necessarily improve the accuracy of wind speed forecast. According to the heavy precipitation weather process in Shandong on August 10, 2019, the two models with different resolutions can simulate the precipitation characteristics well and cover the actual precipitation falling area. The deviation scores of various precipitation grades predicted by the high resolution model are lower than those of the low resolution model. In this heavy precipitation process, the relative humidity was close to saturation on the precipitation day, which was easy to condense, and with the improvement of the model resolution, the relative humidity was enhanced and the structure became more refined. Meanwhile, the central pressure of the low-level cyclone simulated by the high resolution model was lower than that of the low-resolution model, and the cyclone intensity was greater and the convective precipitation process was stronger.
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QIE Xiushu, ZHU Jiangwan, DI Shaoxuan, LUO Shuoming, HUANG Zifan, LIU Dongxia, ZHANG Hongbo, YUAN Shanfeng, LIU Mingyuan, SUN Zhuling, XU Chen, SUN Chunfa, WANG Dongfang, JIANG Rubin, YANG Jing
Available online:August 09, 2023 DOI: 10.3878/j.issn.1006-9895.2306.23307
Abstract:Atmospheric electricity mainly studies the electrical processes occurring in the Earth"s atmosphere and near-Earth space as well as their mechanisms and effects. The core research contents are lightning physics and thunderstorm electricity. Since the 1980s, Atmospheric electrical research has continuously made new progress in China. Thanks to the advances in high-time-resolution lightning detection technology, the research on atmospheric electricity has not only achieved important results in the aspects of lightning physics and thunderstorm cloud charge structure, but also in the impact of lightning and thunderstorms on the near-Earth space, and the characteristics of lightning in strong convective weather, and lightning data assimilation and early warning and forecasting of lightning have made important progress. This paper summarizes recent research progress of atmospheric electricity in China in the past five years from six aspects, including high-precision lightning detection technology, lightning physical process and mechanism, the impact of thunderstorms on the middle and upper atmosphere, observation and numerical simulation of thundercloud charge structure, characteristics and forecast of lightning in strong convective weather, the impact and response of lightning on climate change, etc. Based on this review, key priorities for future research on the atmospheric electricity are highlighted.
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Available online:August 09, 2023 DOI: 10.3878/j.issn.1006-9895.2306.22197
Abstract:This paper uses the GFS (Global Forecast System) global numerical weather forecast product of NCEP (National Centers for Environmental Prediction) as the initial field of the model forecast, and uses the regional mesoscale forecast system CMA-MESO (China Meteorological Administration Mesoscale Model) (formerly GRAPES_MESO) version 5.1 to analyze a rainstorm process that happened in Sichuan Basin on September 3-5, 2021, Five groups of experiments were designed with three different resolutions (1km、3km、10km) and two cloud microphysical parameterization schemes (WSM6、Thompson) for numerical simulation,The results show that: (1) The simulated rain belt in the test is basically consistent with the actual situation, but there are differences between the time, area and intensity of heavy rainfall. With the increase of precipitation threshold, TS score decreases while Bias amplitude increases, which lead the rate of false report and missed report also increases. (2) There is no significant difference in the simulation results of water vapor flux between the same resolution cumulus parameterization scheme and different microphysical schemes; There are strong updraft in the simulated rainstorm regions of the five groups of experiments, and the simulation intensity increased with the increase of resolution. (3) The simulation results of liquid particles with different cloud microphysics schemes at the 1km resolution are similar, but the results of solid particles are obviously different. (4) When cumulus parameterization scheme is added to the 3km resolution, there is a large deviation for the simulation results of heavy precipitation center. On the whole, the experimental simulation results of the precipitation process show that under the condition of high resolution, the saturation adjustment scheme of Thompson scheme is slightly better than that of WSM6 scheme, and the 1km_thompson scheme is more accurate in depicting rain belts, and the precipitation simulation is the best.
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HUANG Lijun, CUI Xiaopeng, CHEN Liqiang
Available online:July 13, 2023 DOI: 10.3878/j.issn.1006-9895.2304.23030
Abstract:In this study, 3730 cold vortexes (CVs) in Northeast Asia from 2000 to 2019 are objectively identified and tracked, including "short duration" CVs that last [6, 24) and [24, 48) hours and traditional northeast CVs that last at least 48 hours. Differences in the spatial and temporal distribution, intensity, and scale characteristics of CVs of different durations, and their impact on precipitation over Northeast China during warm seasons, are further investigated. The results show that: (1) CVs with a duration of [6, 24) hours are the most common, accounting for about 60%, while traditional CVs are the least, about 15%. (2) CVs are more likely to occur from May to August, but CVs with different durations peak in different months. (3) The high occurrences of CV centers with durations of [6, 24), [24, 48), and ≥48 hours appear in the northeast corner, northeast quadrant, and central part of the identification region, respectively. The first moments of CV centers mainly occur near the western boundary between 45°–55°N, and CV centers with a duration of [6, 24) and [24, 48) hours are also more frequent in the northeast quadrant and north-central part, respectively. The last moments of CV centers are located near the eastern boundary of the identification region north of 40°N. (4) The longer the CVs last, the stronger the CV centers and the larger the CV sizes. The CVs are stronger and larger in cold seasons than in warm seasons. (5) The average ratios of total precipitation and short-time heavy precipitation under CVs are both more than 60% (the latter is larger). The longer the duration of CVs, the larger the ratios. The spatial distributions of total precipitation and short-time heavy precipitation under different durations of CVs present remarkable differences. The research on “short duration” CVs also needs more attention.
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YE Mao, WU Zheng, ZHAI Danhua, CHEN Fajing
Available online:July 07, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22173
Abstract:Based on hourly precipitation forecast data with lead time of 12–36 h for CMA-MESO staring at 08:00 BT and hourly gauge-satellite-radar merged precipitation products in the summer (June to August) of 2020, the performance of CMA-MESO for precipitation forecast in Sichuan Basin and the surrounding areas is thoroughly evaluated in terms of hourly precipitation characteristics. The results show that CMA-MESO can capture the spatial distribution characteristics of summer precipitation. The observed larger values of hourly mean precipitation amount and precipitation frequency are located in the high altitude mountains in the west, north and east of Sichuan Basin, and the observed larger values of precipitation intensity are mainly located on the windward slope of the mountains, but the large centers of forecast precipitation amount and precipitation frequency are located in the south of observations. CMA-MESO reasonably reproduces the diurnal variation of summer mean precipitation which is the eastward-delayed diurnal peak phase of precipitation amount and precipitation frequency in the study region, the bimodal pattern with the diurnal peak in the morning and the sub-peak in the evening of the regional averaged precipitation amount and precipitation frequency and the single diurnal peak of the regional averaged precipitation intensity. However, the diurnal variation phase of forecast leads that of observations. The forecast hourly precipitation amount is larger than observations, and obvious positive deviations mostly occur at night (21:00–03:00 BT) and from afternoon to evening (14:00–20:00 BT), which are mainly contributed by forecast deviations of general rainfall (0.1–10 mm h?1) and heavy rainfall (≥10 mm h?1) respectively, and the large deviations are located from the southeastern margin of the Qinghai-Xizang Plateau to the western Sichuan Basin and in the east and south of Sichuan Basin respectively. The forecast deviation of thermal field and dynamic field combined with the influence of topography is found to be the reason for the forecast deviations of rainfall amount.
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Available online:July 07, 2023 DOI: 10.3878/j.issn.1006-9895.2303.22182
Abstract:The effective radius of cloud particle is a critical parameter in cloud microphysics. It is very important to accurately obtain the distribution characteristics of effective particle radius for the analysis of cloud formation, precipitation and severe weather forecast, and earth-air radiation budget. Based on the measurements of the visible and infrared scanner (VIRS) carried by the tropical rainfall measuring mission (TRMM), the spatial distribution and profile characteristics of the effective particle radius are analyzed for the summer from June to August of 1998 to 2012. The results show that the effective particle radius is not uniformly distributed in space. The particle scales range from 5 to 30 μm, and the local scales can reach more than 30 μm. Moreover, the particles over ocean have larger effective radii than those over land. The standard deviation mostly ranges from 2 to 10 μm, but can reach more than 10 μm in some region. The profile distribution of the effective particle radius in different regions shows that the effective particle radius increases first and then decreases with the decrease of brightness temperature. For the small effective particle radius, the profile over ocean is larger than that over land, and the profile in the northern subtropical zone is larger than that in the southern subtropical zone. For the large effective particle radius, the difference of profile among different regions is small. The standard deviation profile of effective particle radius shows that the maximum standard deviations of small particles, moderate particles and large particles are located at ice cloud, mixing cloud and water cloud regions, respectively. The results of this study provide an observation basis for the model to simulate the distribution characteristics of the effective radius of cloud particles in the tropical and subtropical regions.
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Available online:July 07, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22222
Abstract:The heavy rainstorm process in Zhengzhou on July 20,2021 caused huge losses to people "s lives and property. However, the precipitation of this rainstorm is extremely strong, and the uncertainty of numerical prediction is great. In order to improve the ability of CMA numerical model to describe the uncertainty of extreme rainfall intensity forecast of such rainstorm, the 3 km horizontal resolution convective scale numerical forecast system (CMA-Meso 3km) is used to carry out the convective scale ensemble forecast experiment by designing the ensemble assimilation observation disturbance scheme and the cloud analysis radar reflectivity filtering threshold adjustment scheme. The uncertainty characteristics of extreme rainfall intensity forecast of convective scale ensemble forecast are evaluated and compared with CMA global ensemble forecast and regional ensemble forecast. The results show that: 1) there is still a certain deviation in the forecast of extreme precipitation based on the convective scale ensemble forecast with 3km horizontal resolution, but the extreme rainfall intensity values of different ensemble forecast members have good spread, and the extreme rainfall intensity values of individual members are close to the actual 624.1mm, which better represents the forecast uncertainty of extreme precipitation. 2) By comparing the extreme rainfall intensity, dispersion and cumulative precipitation neighborhood fraction skill scores of CMA ensemble forecasts with different resolutions, it is shown that the extreme rainfall intensity and dispersion are closely related to the horizontal resolution of the model. The higher the resolution, the higher the probability forecast skill of extreme rainfall intensity indicating that the convective scale ensemble forecast can better describe the uncertainty and extremeness of extreme rainfall intensity forecast. 3) The convective-scale ensemble forecast that simultaneously disturbs the conventional observation data and radar data can affect the model water vapor field and circulation situation in a short forecast period, which promotes the development of precipitation forecast ensemble dispersion in a short forecast period and effectively improves the probability forecast ability of extreme rainfall intensity. In general, the convective-scale ensemble forecast by disturbing conventional observation data and radar data is helpful to improve the probability forecast skill of extreme rainfall intensity.
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Available online:July 07, 2023 DOI: 10.3878/j.issn.1006-9895.2303.23002
Abstract:Based on CN05.1 observation grid data and Coupled Model Intercomparison Project Phase 6 (CMIP6) model simulation data, the study comprehensively evaluated the simulation capability of CMIP6 models for self-calibrating Palmer Drought Severity Index (scPDSI) in China, and selected 7 models ensemble with relatively good performance to project the change characteristics of scPDSI, runoff and soil moisture in China in the 21st century, and on this basis, the study analyzed the uncertainty of CMIP6 future projection. The results show that the simulation capability of CMIP6 models for scPDSI over China still needs to be improved, the simulation performance of MME is better than most individual models, but there are still deficiencies in temporal trend and amplitude. The temporal trend of scPDSI shows a slight increasing trend under SSP1-2.6 and SSP2-4.5 scenario, the trend values are respectively 0.03/10a and 0.01/10a, and a decreasing trend under SSP5-8.5 scenarios (-0.05/10a). Soil moisture show decreasing trends over time, the trend values of top-10-cm-layer soil moisture and total soil moisture are -0.30%/10a and -0.26%/10a in the SSP5-8.5 scenario, respectively. Runoff show increasing trends over time, the trend values of surface runoff and total runoff are 1.76%/10a and 3.13%/10a in the SSP5-8.5 scenario, respectively. At the end of the 21st century, the annual scPDSI over China generally decreases under higher emission scenarios, the change of soil moisture is generally "high in the North and low in the South", the downtrend is most significant in the Qinghai-Tibet Plateau region, and the change range of surface soil moisture is bigger. Runoff tends to rise in most areas, except Northwest China and the Qinghai-Tibet Plateau region, and the change range of it is bigger under higher emission scenarios. The probability density curves of most variables in the 21st century flatten under higher emission scenarios, so that the future changes become more dramatic.
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Available online:July 07, 2023 DOI: 10.3878/j.issn.1006-9895.2305.22205
Abstract:Based on the typical rainstorm cases occurred in the western edge of Sichuan Basin from 2015 to 2018, the environmental field conditions of rainstorm with different spatial distribution characteristics were analyzed, and the reasons for frequent occurrence of night rain in Sichuan Basin were discussed from the perspective of atmospheric diurnal variation characteristics in summer. The results show that: (1) Influenced by the high and steep terrain in the western margin of Sichuan Basin, the air temperature and humidity in the middle and lower layers in the western Sichuan Basin are good, and the warm and humid southeast airflow converges and lifts when encountering the large terrain, which is prone to heavy rainfall. When the rainstorm occurs in the west of the whole basin (west type), the humidity in the west of the whole basin is very high and the southeast wind is strong; When the rainstorm occurs in the northwest of the basin (northwest type), the southeast wind in the middle and low levels is the strongest, and the dynamic effect is the most significant; When the rainstorm occurs in the southwest of the basin (southwest type), most of them are accompanied by northerly wind into the basin, and there is an obvious north-south wind shear convergence. The water vapor divergence flux is a good indicator for the intensity and location of heavy rain in the western Sichuan Basin. (2) The diurnal variations of the convective available potential energy, relative humidity, pseudo-equivalent potential temperature, wind field at low and middle levels and divergence all indicate that the precipitation in the western Sichuan Basin tends to occur at night.
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ZHANG Hanbin, SHI Yongqiang, Lu Bing, XIA Yu, WU Zhipeng
Available online:July 07, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22235
Abstract:withtheresolution of numerical prediction system became higher, the Subgrid-scale orographic gravity wave drag(GWD) and low-level blocking parameterization is not suitable. The WRF v4.3 has introduced two additional orographic drag suite, the small-scale GWD and turbulent orographic form drag, thus to form a scale-aware scheme. Application test has been carried out to evaluate performance in high-resolution model covering North China area, three schemes are designed, including shut down the GWD in the model, open the original GWD, and open the new scale-aware GWD.The results show that for the original GWD it contains only subgrid-scale orographic GWD and low-level blocking without varies with resolution, thus to bring strong affectionto the wind at all levels in the model, but not always positive. The scale-aware GWD scheme can minimize the aforementioned two stress to zero while keep small-scale GWD and turbulent orographic form drag in 3km model,therefore the drag force only in the Planetary Boundary Layer(PBL) and the low-level wind can be effectively improved.The statistical results show that scale-aware GWD can significantly decrease the positive biasand the RMSE of near surface wind forecast, but for other variables the improvement is not significant.
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HuangJiaWei, WangYongQian, WuXiaoJuan
Available online:July 04, 2023 DOI: 10.3878/j.issn.1006-9895.2305.22098
Abstract:Based on the daily meteorological observation data of 158 stations in Sichuan Province and the road meteorological disaster data from 2018 to 2020, the correlation analysis is used for a total of 14 factors including temperature, humidity and Precipitation Factors and their daily variation composite characteristics to study the difference of road icing modes under plain and mountainous terrain. The results show that the correlation coefficient between average relative humidity and icing is 0.451 and -0.451 in the two terrain respectively. The difference of icing mode in mountainous and plain terrain is mainly reflected in the different factors that meet the water vapor conditions required for icing. In addition, based on the dimensionality reduction of principal components, stepwise regression and lasso principle, the logistic icing prediction model is constructed, the accidental error is reduced by 50% cross validation, and the obtained model is evaluated by using the standards of accuracy, ROC curve and AUC value. The performance of the three models under the two terrains ranked the same. Lasso-Logistic model had the best effect, with an average accuracy of 86.98%, followed by SR-Logistic, with an average accuracy of 84.05%, and PCA-Logistic was the lowest, with an average accuracy of 84.09%. In the typical case test, the prediction accuracy of Lasso-Logistic in plain and mountainous areas is 86.15% and 83.70% respectively, which is the highest among the three models. At the same time, the introduction of the composite characteristics of meteorological factors over time can improve the prediction accuracy of the model. Among them, Lasso-Logistic, PCA-Logistic and SR-Logistic have improved the accuracy of the model by 3.68%, 3.00% and 3.00% compared with the model with only daily mean. The results show that lasso logistic icing prediction model can effectively predict road icing events under two kinds of terrain, has strong universality, and can provide reference for road icing disaster early warning.
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Chang Youzhi, Zhang Jie, Li Na, Ran Lingkun
Available online:June 14, 2023 DOI: 10.3878/j.issn.1006-9895.2305.22242
Abstract:The paper conducts a high-resolution numerical simulation of an extreme rainstorm process that takes place under complex topographic conditions in South Xinjiang, utilizing the WRF model. Additionally, water vapor sensitivity experiments are carried out to investigate the impact of water vapor on extreme rainstorms in the arid zone of South Xinjiang. Through these experiments, the mechanism of how water vapor affects the rainstorms in South Xinjiang via dynamic-thermal coupling is initially uncovered. Further investigation into the characterization ability of the generalized wet level vortex and convective vorticity vector reveals their impact on heavy rainfall in arid zones. The study concludes that changes in water vapor have a significant effect on the intensity of precipitation extremes. Specifically, an increase in water vapor results in a significantly higher change in precipitation intensity than the change in water vapor itself. This effect is most pronounced when low-level water vapor is enhanced, and when mid-level water vapor is increased, the extremity of precipitation is also significantly enhanced. Furthermore, the study found that the change in precipitation intensity is linear within the first hour of changing water vapor. This is attributed to the fact that changing water vapor significantly alters the Convective Available Potential Energy (CAPE) of the precipitation atmosphere. The stronger the CAPE, the more potent the convective trigger becomes, leading to stronger vertical motion that can further pump lower level water vapor. This positive feedback mechanism results in extreme precipitation. Sensitivity experiments reveal that increasing water vapor significantly enhances upward motion, the strength of the low-level easterly rush, and the water vapor convergence in the precipitation zone. This leads to an increase in water vapor transported to the mesosphere and an increase in the release of latent heat of condensation, further amplifying upward motion and increasing precipitation intensity. Conversely, decreasing water vapor results in a significant reduction in upward motion, the strength of the low-level easterly rush, and the water vapor convergence in the precipitation zone. As a result, the water vapor transported to the middle layer decreases, and the latent heat of condensation in the middle layer decreases, leading to a reduction in upward motion and a decrease in precipitation intensity. The simulated precipitation exhibits a strong correlation with the spatial distribution and temporal evolution of both the generalized wet vortex and convective vorticity vectors. This correlation is particularly evident following changes in water vapor, as the characteristics of both vectors display similar changes. These results suggest that the rich dynamic and thermal information contained in these physical factors can effectively capture the key features of extreme precipitation in arid regions. Moreover, by coupling these physical factors with precipitation data, they may prove useful in the early warning and prediction of precipitation in the future, particularly in arid areas. Therefore, the coupling of these physical factors and precipitation has the potential to improve the accuracy of precipitation forecasting in arid zones.
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YinQiuchao, WangLu, GeZian, GaoQingjiu
Available online:June 08, 2023 DOI: 10.3878/j.issn.1006-9895.2305.22245
Abstract:Based on the daily maximum temperature data (CN05.1) in China during 1961-2017, this paper reveals the dominant modes of the interannual variation of the number of summer extremely high-temperature days (EHTD) in China through empirical orthogonal function analysis (EOF), and explores the key influencing factors and related physical mechanisms that lead to the formation of each mode. The results show that the first mode is the zonal distribution across China, which is mainly related to the Arctic Oscillation (AO). The Rossby wave train propagating southward from the northern Europe strengthens the zonal high anomaly across China when the AO is in a positive phase. The second mode shows the meridional dipole pattern, which is mainly influenced by the Polar-Eurasian teleconnection (POL) wave train spreading from North Atlantic Ocean to East Asia and the sea surface temperature anomaly over the western tropical Pacific enhances local Hadley cell, which makes the south (north) of China under the control of high (low) pressure systems. The increase of EHTD in the first two modes is related to the increase of incident solar radiation caused by the decrease of precipitation caused by local high-pressure anomalies. The distribution of the third mode is concentrated in the Tibetan Plateau (TP), which is mainly influenced by the zonal wave train propagating downstream from the Mediterranean Sea. On the one hand, the circulation anomaly corresponding to the wave train will cause the divergence of water vapor and the weakening of upward motion, which will decrease the cloud cover and increase the downward cloudy-sky shortwave radiation; on the other hand, it will cause atmospheric warming, which will increase the downward clear-sky longwave radiation. Both of them provide favorable conditions for the increase in the number of extremely high-temperature days. The results of this study will help to further understand the characteristics of summer extreme high temperature in China, and provide a theoretical basis for the seasonal prediction of extreme high temperature.
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ZHANG Xin, WANG Qiuping, MA Xulin, ZHANG Xupeng, CHENG Wei, XIA Yuancai
Available online:June 08, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22224
Abstract:An accurate and objective evaluation of its performance is of great significance to the improvement and development for the new observation system. Our new generation of round-trip drifting sounding system (RDSS) breaks through the traditional sounding observation mode innovatively and realizes the “up-drift-down” three-stage observation through one release, which expands the ability and scope of existing sounding observation. The sensitivity of forecast in the middle and lower reaches of Yangtze River to the new Round-trip Drifting Sounding observation data was studied based on forecast sensitivity to observations (FSO) method in this paper. The result shows that the assimilation of conventional observation can reduce the forecast error and improve its quality in different degrees, in which the wind and temperature observation contributed most significantly. The new Round-trip Drifting Sounding observational data has more significant contribution to the forecast in the target area of the middle and lower reaches of Yangtze River. The forecast error of 71.4% times in the test period was further reduced after data assimilation combined the new RDSS data, and the meridional wind and humidity observation contributed mostly. What’s More, the contribution of its wind observation has obvious spatial difference where the large value areas of forecast error reduction are mainly distributed in the test station and its vicinity. In addition, the wind, temperature and humidity observation of new data in the whole layer have a significant positive contribution to the forecast quality, while the zonal wind observation in the middle and lower troposphere have a weak negative contribution.
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maoying, kouleilei, wangzhixuan, chenyao
Available online:May 18, 2023 DOI: 10.3878/j.issn.1006-9895.2305.22168
Abstract:The classification of rain types is essential to understand the microphysical characteristics of regional precipitation, the construction of multi-source precipitation fusion error model, and the radar quantitative precipitation estimation. Based on the C-band dual-polarization radar data of Nanjing University of Information Science and Technology and the observation data of raindrop disdrometer in Nanjing from 2015 to 2016, this paper proposes a radar rain type classification method applicable to Nanjing area, and compares and verifies the classification results of rain types. Firstly, 36 typical stratiform and convective precipitation processes were filtered out based on the time series data of the rainfall rate of raindrop disdrometer, the ground-based radar reflectivity factor Plane Position Indication (PPI) and Time Height Indication (THI). Then, the raindrop size distribution (DSD) parameters of typical stratiform (convective) precipitation at three raindrop disdrometer stations were counted: normalized droplet number concentration (NW) and median raindrop diameter (D0), and the log10(NW)-D0 classification line applicable to Nanjing area was fitted. The classification line based on the raindrop disdrometer data is applied to the ground-based radar DSD parameters retrieved based on the variational method to classify the ground-based radar rain types. According to the time-height distribution of rain type separation index in typical stratiform (convective) processes, and comparing with DPR precipitation classification products, the classification effect is verified. Finally, the classification results are applied to radar classification quantitative precipitation estimation to further illustrate the application effect of precipitation classification. The results show that the fitting classification lines of the three raindrop disdrometer stations in Nanjing are very consistent, and the typical stratiform (convective) processes of three stations can be well separated on both sides of the classification line; Compared with the DPR precipitation classification products, it is found that the classification effect of the classification line in Nanjing is higher than that of other typical rain types classification methods, and the recognition rate of stratiform and convective precipitation is the highest, with 84.56% and 72.64% respectively; The accuracy of radar quantitative precipitation estimation based on rain type classification is better than that of unclassified rain measurement formulas, and classified R(Kdp) has the best performance among all classified rain measurement formulas (CC=0.7648，MAE=3.0952 mm/h，RMSE=5.4297 mm/h).Classified R(Zh) has the best performance in stratiform precipitation retrieval, classified R(Kdp) has the best performance in convective precipitation retrieval, while classified R(Zh,Zdr)has the most obvious improvement on the accuracy of the original rain measurement formula.
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WU Zeyi, GUO Fengxia, LU Xian, LIU Zhou, DENG Jie, CHEN Ke, WANG Qingyuan
Available online:May 18, 2023 DOI: 10.3878/j.issn.1006-9895.2305.22215
Abstract:In order to further understand the impact of updraft on the complex charge structure characteristics within thunderstorm clouds, the WRF model with electrification and discharge parameterization scheme is used to simulate the process of a strong thunderstorm with inverted charge structure on June 6, 2012 in the DC3 experiment. The results show that the electrification region corresponds to the strong echo region, which mainly occurs in the ice-water mixing region with cloud water content greater than 0.2 g/kg in the updraft region. The non-inductive electrification mechanism dominates the electrification process in thunderstorm clouds. There is considerable charged particles in the periphery area of the updraft, which is mainly formed by the backward horizontal transport of charged particles from the electrified area by the airflow. The polarity of homogeneous particles change little in a large range, but the net charge distribution presents more complex due to the different content and charge of particles. The updraft with a certain intensity can destroy the continuity of the charge area, resulting in a high-density and smaller area with positive and negative staggered distribution in the convection region. Since there is no updraft in the stratiform area, the charged particles mainly come from the horizontal transport in the updraft area, so the charge structure in the stratiform cloud area is relatively continuous and wide, but the charge density is relatively weak. Due to the different intensity and inclination degree of updraft in different cell life periods, there are certain differences in the distribution characteristics of hydrometeor particles among cells, which makes their reversal temperature and electrification rate significantly different. Therefore, the charge area in the updraft area becomes more fragmented and the charge structure becomes more complex during the merger.
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ZHANG Wei, CHEN Dehua, CUI Mengxue, WANG Jing, HU Yajun, WU Bingui
Available online:May 15, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22088
Abstract:Using fog droplet spectrum data in Xiangan from 2019 to 2021, We investigated the statistical characteristics of micro-physical parameters and fog droplet spectrum of sea fog in Southern coast of Fujian. Based on the relationship between visibility and particle number concentration(N), liquid water content(L) of fog and relative humidity(RH), We established various parameterization schemes and evaluated the fitting effect of each scheme. The results showed that average N and L of sea fog in Southern coast of Fujian was 47.5 cm-3 and 0.0763 g·m-3. N and L increased significantly with the enhancement of fog level while mean diameter, effective diameter increased slowly. When visibility drop below 100 m, average N and L reached 115.42 cm-3 and 0.228 g·m-3. N and L spectrum both exhibited double peak characteristic. Main peak of N located in 4～6 μm and secondary peak was in 22～26 μm. L showed opposite characteristic with peak value in 24～26 μm and secondary peak in 4～6 μm. This showed that N of fog is mainly controlled by small droplets, but particles of 20～30 μm contributed more to L. Compared with other coastal regions, average N of Southern coastal Fujian was smaller than southern coast of China but larger than eastern coast of China. Average L was larger than southern coast but smaller than eastern coast. Compared with inland regions such as city or country sites, N of the same fog level was smaller but L was larger. Four parameterization schemes of visibility were established by using full samples and segmented method. Test results indicated that visibility subsection fitting scheme based on L×N was optimal, especially for visibility below 1 km .
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LI Jiaqing, XU Haiming, DENG Jiechun, MA Jing
Available online:May 15, 2023 DOI: 10.3878/j.issn.1006-9895.2305.22172
Abstract:Based on the ERA5 daily reanalysis data from 1979 to 2019, the self-organizing mapping (SOM) analysis is performed to objectively classify tropospheric polar vortex over the northern hemisphere in winter, analyze the temporal variation characteristics of the polar vortex weather pattern, and reveal its causes of the long-term variation. Results are shown as follows: (1) According to the center position of the polar vortex, it can be divided into circumpolar type, dipole type, Eurasian type and North American type, in which the circumpolar and dipole types are the dominant circulation types. The circumpolar and dipole types show a significant decreasing and increasing trend respectively, with obvious interannual and interdecadal variability. (2) The long-term decrease of the circumpolar type and the long-term increase of the dipole type are mainly due to the rapid warming of the Arctic region, which leads to the continuous reduction of the meridional temperature gradient and the weakening of baroclinicity between the middle and high latitudes of the northern hemisphere. The weakening of the circumpolar westerly circulation weakens the strength of the polar vortex in the northern hemisphere, which makes it very easily to split. Then, based on the data of the pre-industrial control simulation (piControl) and the simulation forced by a 1% /yr CO2 increase (1pctCO2) with Ocean-Atmosphere Coupled Model (CESM2) for the Coupled Model Intercomparison Project Phase 6 (CMIP6), SOM is also used to further explore the relationship between the long-term variability of circumpolar and dipole type and global warming. It is found that the circumpolar and dipole types are still the dominant circulation types in piControl and 1pctCO2. The circumpolar and dipole types have no significant variability trend in piControl, but show a significant decreasing and increasing trend respectively in 1pctCO2, which further verifies that the long-term variabilities of two polar vortex weather patterns under observation are closely related to global warming.
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Available online:May 15, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22227
Abstract:This study tried to establish a precipitation dataset over China in the last 120 years. The precipitation records before 1950 rescued by CMA and in-situ measurements from the national observatories after 1950 were merged to obtain long time series since 1900s. 2446 daily and monthly precipitation time series comprise this dataset in which 321, 126 and 60 sequences have records earlier than 1945, 1930 and 1915, respectively. The breaks caused by inhomogeneity issues in historical data were checked and removed by PMF, PMT and QM methods respectively. 113 breakpoints from 107 stations were identified which significantly deviated the precipitation and seasonal variability from the regional climate state. The homogenizing adjustments eliminate these surges and slumps in historic data induced by non-climatic factors. The homogenized data show much higher spatial and temporal consistency with neighboring measurements. Based on the homogenized data, the precipitation amounts over China showed slight changes in last 120 years, the change rate of the precipitation anomalies percentage from 1900 to 2022 was around 0.35±0.21 %/10a.
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XIAO Liusi, ZHANG Hualong, WU Naigeng, FENG Lu, LIU Wenjun
Available online:May 12, 2023 DOI: 10.3878/j.issn.1006-9895.2302.22130
Abstract:In order to improve the understanding of the development of extreme precipitation at smaller time scale in South China monsoon region, the spatial and temporal distribution of 5-minute extreme heavy rain and persistent characteristics of extreme rainfall events in flood season were analyzed based on the 5-minute precipitation observation data of automatic weather stations from 2013 to 2021, and compared with the characteristics of hourly extreme precipitation. The results show that the 5-minute extreme precipitation threshold (E5min) has a significant meridional difference, forms a high-value center in the Pearl River Delta region and is generally less affected by the inherent influence of topographic mountains. However, the 1-hour extreme precipitation threshold (E1h) decreases from the coast to the land, and the high value area is mainly located on the windward slope of the southerly wind terrain. In the pre-flood season, E5min decreases from southwest to northeast, and distributes relatively evenly in the post-flood season. Different from the diurnal variation characteristics of hourly extreme precipitation, E5min in the pre-flood season all have a double-peak structure (the main peak in the afternoon, while the secondary peak in the morning), but only the 3 regions adjacent to the Pearl River estuary have double-peak structures in post-flood season, and the rest are unimodal. The longer average duration of extreme precipitation at each station, the more obvious spatial differences, with the longest duration in the southern coast, followed by the central region, and the shortest duration in the north. Further summarizing the extreme events with spatial and temporal correlations, it is found that daytime extreme events are more frequent, move faster, and have a wider range than nighttime events, while nighttime events last longer. Among them, the moving speed of the inland precipitation system is faster than that of the coastal area, especially in the Yunfu-Zhaoqing area, resulting in a high precipitation efficiency in 5 minutes, but a low hourly threshold. The duration of extreme precipitation events in the central and southern coastal areas of the Pearl River Delta is the longest (up to 2.34-3.65 hours at night), which may be related to the comprehensive effects of urban agglomeration and sea-land effect in this region.
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Available online:May 06, 2023 DOI: 10.3878/j.issn.1006-9895.2304.23015
Abstract:Northeast China cold vortex (NCCV) often induces low temperature and cold damage in Northeast China during summer, resulting in "Dumb Disaster" to the "Northeast Granary". Using the fifth-generation reanalysis data of ECMWF, this paper analyzes the key circulation configuration, as well as formation and maintenance mechanism of NCCV with low temperature impact during early summer (May–June) over 1979–2021. The results show that two ridges over Lake Baikal and the Okhotsk Sea as well as NCCV form a typical inverted "Ω" circulation, which favors invasions of cold air and high potential vorticity from the high latitude region into Northeast China. At the same time, easterlies on the south flank of high over the Okhotsk Sea bring cold air into Northeast China. These two cold air intrusions together cause the abnormally cold in Northeast China. The "- + -" Rossby wave train from the eastern European Plain to Lake Baikal is the precursor of NCCV, which is incipiently amplified by the diabatic heating and friction. Subsequently, the Rossby wave plays a major role, which causes the high potential vorticity intruding southward and accumulating. The East Asian jet barotropically deforms such high potential vorticity to form a deep NCCV. As the downward dispersion of Rossby wave energy and the dissipation of diabatic heating and friction, NCCV weakens drastically. When the quasi-stationary ridge maintains over the north of Lake Baikal, it cuts off the connection between Northeast China and the cold air and high potential vorticity over the high latitude region. The Rossby wave hardly leads NCCV to develop and thus NCCV has no obvious low temperature impact over Northeast China.
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DAI Qiudan, Guo Zhenhai, Wang Longhuan, Sun Xiangming, Xie Zhenghui, Sun Shufen, and Xiao xia
Available online:May 06, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22186
Abstract:Using the ERA5 single-layer reanalysis data combined with the planetary boundary layer tower (PBL tower) meteorological observations from a north-south climate transition zone mountainous forest in Huainan as forcing data, we evaluate the applicability of the Community Land Model (CLM4.5) against observed canopy flux and micrometeorological data at this site. Also three experiments to study the impact of soil texture on soil moisture are designed to improve the model performance. The results show that overall CLM4.5 performances good in Huainan mountainous forest, and the simulated results driven by observation is better than that of ERA5 data. In terms of radiation simulation, both the simulated results of the radiation components using ERA5 data and PBL tower observation data are good, especially driven by PBL tower observation, and the correlation coefficient between the simulation results and observations throughout the year is more than 0.97, and the root mean square error is below 25.056 W m-2. The correlation coefficient of the ERA5 forcing simulation is slightly lower, but it also reaches 0.92, and the root mean square error is below 29.939 W m-2; In terms of soil temperature, both the correlation coefficients reach more than 0.98; the correlation coefficients of soil moisture results are all above 0.86, but systematically higher; and the average correlation coefficients of the simulated results of the sensible heat flux are 0.72 and 0.78, respectively. Through the comparison simulating tests of three soil texture parameters, it is shown that the simulated results of the soil moisture with the measured three layers of soil texture plus the data of the deep soil texture are closest to the observation. Thus the accurate description of the soil texture can greatly improve the simulation of soil moisture. But further tuning of the parameters or parameterization scheme is still needed. In addition, the ERA5 reanalysis single-layer data as forcing in this site are reliable, and thus can be used in the further simulating work. This study could be useful for further study of land and atmosphere exchange in the north-south climate transition zone of Huainan, China.
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Available online:April 28, 2023 DOI: 10.3878/j.issn.1006-9895.2212.22243
Abstract:Using HadISST and ERSSTv5 SSTs, CMAP precipitation and ERA5 reanalysis data, this paper studies the relationship between spring sea surface temperature (SST) in the North Pacific and autumn precipitation in the the Maritime Continent. The results show that: 1) Victoria mode (VM) is the second mode of EOF analysis of spring SST in the North Pacific, which has a significant negative correlation with autumn precipitation in the Maritime Continent. 2) When VM is in positive (negative) phase in spring, it is usually accompanied by the positive (negative) phase of the Pacific meridional mode and the cold (warm) SST anomaly in the Northwest Pacific. The SST gradient would lead to the westerly (easterly) anomaly in the equatorial Pacific, impacting eastward propagation of equatorial Kelvin wave and leading to warm (cold) SST anomaly in the central and eastern Pacific. SST gradient and westerly (easterly) anomaly persist into autumn through Bjerknes feedback, so the mature El Ni?o (La Ni?a) event forms in autumn. Then, through the Walker circulation, the abnormal sinking (rising) movement, low-level divergence and high-level convergence (low-level convergence and high-level divergence) over the Maritime Continent occur, resulting in precipitation deduction (increase). 3) This interannual relationship between the variation of springtime VM and the autumn precipitation over the Maritime Continent has changed in 2003, which was a significant negative correlation from 1979 to 2002, but was insignificance from 2004 to 2020. The reason for this decadal change is that the North Pacific Oscillation altered from 2004 to 2020, which led to the weakening of the influence of the North Pacific Oscillation on the key area of southern SST part of VM, thus weakening the amplitude, weakening the meridional gradient of the key area of SST between the southern and northern part of VM, weakening the VM amplitude, and finally reducing the correlation coefficient.
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Wang Ting, Zhu Congwen, Ma Shuangmei
Available online:April 28, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22188
Abstract:The rainy season in China is mainly regulated by the annual cycle of East Asian summer monsoon (EASM), showing a significant year-to-year variation. Based on the daily precipitation in China and the atmospheric reanalyzed data, we analyzed the trends of EASM onset, withdrawal and duration, as well as the rainy season in China during 1961?2020. Our results show the EASM onset and withdrawal has advanced and delayed by 3.54 days and 1.64 days, respectively. And the duration has increased by 5.18 days per decade since 1961. The rainy season in China has changed before and after1999 with spatial differences. In contrast to the past two decades (1977?1998), the onset of rainy season in recent years (1999?2020) has advanced mainly in the eastern part of the Northeast China, Qinghai-Tibet Plateau and the north of Northwest China, where the advanced rainy onset was 5 days earlier, and exceeded 20 days in some areas. The withdrawal of rainy season has delayed more than 10 days in northeast of the Qinghai-Tibet Plateau, north and west of the Yangtze River. The change of onset and withdrawal resulted in a sharply increased rainy duration in northeast of Qinghai-Tibet Plateau, north of Yangtze River, and the southeastern part of the Northeast China, where the rainy length became more than 15 days longer and more than 25 days in some areas. The warming surface air temperature (SAT) around Lake Baikal with enhanced upper-level anticyclone in April are the key to the onset advance of the EASM and the rainy season in China. The warming of the northwest Pacific Ocean SST in October with enhanced subtropical anticyclone in the northwest Pacific are the key factors leading to the withdrawal delay of the EASM and the longer rainy season in northern China. When the warming of SAT and SST in these two regions are superimposed with the La Ni?a events, the duration of EASM and the rainy season in China becomes much longer on interannual time scale.
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Sun Yankun, Xin Huajian, Xu Min, Wu Tong, Zhao Shunman, Xu Dongxin, Zhou Yongji, Hu Bo
Available online:April 28, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22178
Abstract:Based on the radiation data observed in Beijing from 2005 to 2020,the variation law of Ultraviolet(UV) radiation in Beijing in recent ten years is revealed, and the main factors affecting the long-term variation of UV radiation are analyzed. The results show that the UV radiation shows obvious diurnal and seasonal variation characteristics.The diurnal variation showed a single peak pattern, with the maximum value appeared at noon, and the low value in the morning and evening,and the maximum value and minimum value appeared at 12 noon (16.26 W/m-2) and 8 PM (5.64 W/m-2) ,respectively.The ultraviolet radiation gradually increased from spring to annual maximum in summer, and then began to decline until annual minimum in winter. The monthly average maximum and minimum appeared in June (12.17 W/m-2) and December (5.4 W/m-2),respectively.The annual mean value of UV radiation was 9.74 W/m2.The ultraviolet radiation is positively correlated with clearness index and negatively correlated with aerosol optical depth (AOD) and PM2.5.
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Available online:April 28, 2023 DOI: 10.3878/j.issn.1006-9895.2304.22175
Abstract:To insight the performance of numerical weather prediction model on refined heavy rainfall, a neighborhood verification method named Fractions Skill Score (FSS) is introduced to examine the capability of six operational models on 3h-accumulated precipitation during the warm season in 2019 in Zhejiang Province, with particular focus on short-term torrential rain and the impacts of different weather backgrounds. The results show that: (1) Based on the cumulative climatological probability of station 3h-accumulated precipitation, the FSS method is improved by determining the skill score thresholds for 5 grades precipitation with thresholds of 0.1, 3.0, 10.0, 20.0 and 50.0 mm/3h as 0.583, 0.522, 0.506, 0.502, and 0.500, respectively, and applied in the assessment of their prediction skill scales in the long time series. (2) The regional models outperform the global models in heavy rain forecasts, only the mean scores of Shanghai Regional Numerical Weather Prediction System (CMA-SH9) and Zhejiang Regional Numerical Weather Prediction System (CMA-ZJ3 and CMA-ZJ9) achieve the forecast skills for torrential rain, and their corresponding skill scale is 159, 159, and 183 km. There are about 60% of forecasts in these models achieve the prediction skills, and the cumulative frequency of the skill scale is increased by nearly 50% from 3km to 183km. This scale-selective evaluation result can provide a reference for the application of model products at different scales. (3) The differences in the models performance of precipitation forecasts under various weather backgrounds are obvious. The best model for predicting torrential rain under the background of tropical cyclones, Mei-Yu fronts and weak-synoptic forcing is the Global Forecast Model from European Centre for Medium-Range Weather Forecasts (EC-GFS), the CMA-SH9 and the CMA-ZJ3, with skill scales as 27, 99, and 135 km. Therefore, the application of model products should be treated differently in terms of weather background type.
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LI Shangfeng, SHAO Qiduo, YIN Luting, GAO Zongting, and LIAN Yi
Available online:April 28, 2023 DOI: 10.3878/j.issn.1006-9895.2212.22139
Abstract:Based on CN05.1 daily mean temperature data with a horizontal resolution of 0.25°×0.25° during 1961-2020, daily NCEP/NCAR reanalysis data and daily sea surface temperature (SST) data from NOAA, this paper analyzed the variation characteristics of the onset dates of spring and their early signals over Northeast China (NEC). The results showed that: (1) The spatial distribution characteristics of the onset dates of spring over NEC appeared a progressively later pattern from south to north. The maximum spring area was mainly concentrated in the 26th and 27th pentad, and the advanced trend was evident in recent 60 years. (2) In the years of spring starting early, positive anomalies of temperature and precipitation appeared over NEC in March, and there was an “Ω” circulation pattern at 500-hPa over the West Siberian plain, Baikal and Kamchatka Peninsula. In the years of spring starting late, negative anomalies of temperature and precipitation appeared over NEC in March, and there was a high pressure ridge in the Ural Mountains with a large-scale tilted ridge on the east side, which atmospheric circulation fields lasted from the 22nd pentad to the 26th pentad. (3) La Ni?a–related SST anomalies appeared over the equatorial central eastern Pacific, positive SST anomalies occurred in the ocean south of Greenland and east of the Philippines in the years of spring starting early, while it was opposite in the years of spring starting late. Moreover, through correlation analysis, it was found that SST anomalies during the preceding winter (December-January-February, DJF), in the ocean south of Greenland and east of the Philippines had better indication for the onset dates of spring.
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LuZihan, LiXiaojing, TangYoumin
Available online:April 28, 2023 DOI: 10.3878/j.issn.1006-9895.2303.22075
Abstract:Using the ADT-HURSAT cyclone dataset produced by the unified satellite observation and identification scheme, the general characteristics of tropical cyclones in the North Indian Ocean (NIO) during the 40-year period from 1978 to 2017 were statistically analyzed. The study found that spring and autumn were the peak seasons for tropical cyclones in the NIO, and that the peak number of cyclones in the Bay of Bengal was about one month earlier than in the Arabian Sea in both peak seasons. Cyclones in the NIO occurred mainly in the eastern waters of the Arabian Sea and the west-central waters of the Bay of Bengal. Cyclones of the Cyclone-Storm class were more common in the North, whereas all cyclones above (including) Extremely-Severe-Cyclone-Storm class occurred within 5 ° N-15 ° N latitude. In the case of interdecadal changes, the number of tropical cyclones in the NIO increased by an average of 5 per decade in the autumn for the decadal change, and the region was characterized as moving northwestward in the next two decades, with tropical cyclones in the Arabian Sea moved 1.3 ?and 3.2? (p < 0.01), more significant than the Bay of Bengal cyclones, with an average intensification rate of about 20% over the Bay of Bengal.Compared to previous 10 years (1998-2007), their number decreased and their maximum intensity increased to 120kt; conversely, their number remained stable since 1998, but their maximum intensity decreased. These conclusions differed from studies using other datasets, indicating that dataset quality was important for analyzing cyclonic characteristics. Further analysis showed that decadal variation in latent heat flux was main factor controlling interdecadal change of tropical cyclone generation area in the NIO.
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LIU Di, TIAN Wenshou, LUO Jiali, ZHANG Ruhua
Available online:April 28, 2023 DOI: 10.3878/j.issn.1006-9895.2105.21040
Abstract:Based on the WRF-Chem model, the characteristics and the mechanisms of the Stratosphere-Troposphere-Exchange (STE) are analyzed in a deep convection that occurred in the southeastern part of the Tibetan Plateau on August 12, 2010. The results show that the strong updraft in the deep convection could directly transport the air with high concentration of CO and low concentration of O3 near the ground into the lower stratosphere, and increase the concentration of CO and decrease the concentration of O3 in the lower stratosphere. The deep convection induced a strong turbulent mixing process, which caused the continuous STE in the Upper-Troposphere-Lower-Stratosphere (UTLS) region within 3-4 hours after the deep convection, transporting the ice crystals, CO and O3 in the troposphere to the lower stratosphere. The water vapor entering the lower stratosphere is significantly reduced because of the condensation and dehydration.
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ZHANG Duanyu, WANG Junchao, WANG Xiaofang, CUI Chunguang, and YE Jintao
Available online:April 24, 2023 DOI: 10.3878/j.issn.1006-9895.2301.22002
Abstract:A continuous heavy rain course lasted in Shandong Province from 9 to 12 August 2019 mainly brought by landing typhoon Lekima. Local rainfall of Shandong peaked at night of 10 August. Reasons why the heavy rain there became the largest at night of 10 are studied by using hourly rainfall data, conventional observation data, Temperature of Black Body (TBB) observed by China FengYun-2G (FY-2G) Meteorological satellite, as well as American National Center of Environmental Prediction (NCEP) reanalysis data. Main method of this paper is diagnostic research by using both equation of zonal horizontal motion and that of atmospheric kinetic energy. The conclusions could be drawn as follows. (1) Main influence systems of the heavy rain were westerly trough on 500 hPa, southwesterly upper level jet, southeasterly low level jet, inverted trough of typhoon Lekima on 850 hPa, as well as typhoon circulation of Lekima itself. A large scale upper level jet of southwester on 200 hPa moved southeastward to affect northwest Shandong Province in 10 August. Another large scale southeasterly low level jet on 850 hPa jumped quickly northward passing Shandong Province at 0800 BJT 10. Convective clouds of both inverted trough and typhoon Lekima circulation itself moved northward over central Shandong Province successively, causing the top rainfall of that area at night of 10 due to cumulative effect. (2) The fastest east wind increasement on 850 hPa appeared at the northeast of Zhangqiu radiosonde station around 2000 BJT 10 during the rainstorm course. Results show that the main reason why east wind augmented was advection of east wind, but geostrophic deflection force term wasn’t conducive to easterly increasement. (3) Southwester jet emerged at 200 hPa at Zhangqiu radiosonde station at 2000 BJT 10, southeaster jet maintained at 850 hPa at Qingdao radiosonde station from 0800 BJT 10 to 0800 BJT 11. The rain reached its peak at night of 10 in the middle of Shandong Province, because the region was not only at the right and rear of upper level jet, but also at the left and front of low level jet simultaneously. Both kinetic energy at Zhangqiu on 200 hPa and that at Qingdao on 850 hPa augmented fastest 12 hours before wind speeds reached their maximum value of those days. Results diagnosed through kinetic energy equation show that, the item most favorable to upper level wind speed increasement on 200 hPa near Zhangqiu station was advection of potential energy, and the item most favorable to low level wind speed increasement on 850 hPa near Qingdao station was divergence of kinetic energy vertical flux. (4) Although typhoon circulation of Lekima itself acted on Shandong from 2000 BJT 10 to 0800 BJT 13, and the dynamic role of mountains in central Shandong had always been there in the course, the rainstorm there just broke out at night of 10 August. It shows that, the coupling of upper level jet with low level jet at that time might be the major factor of raising the rainfall intensity. Its roles were strengthening ascending motion, raising the whole layer water vapor transportation and adding atmospheric static instability in the central Shandong at least.
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Available online:April 24, 2023 DOI: 10.3878/j.issn.1006-9895.2302.22108
Abstract:Based on Doppler weather radar data, ERA5 reanalysis data and ground automatic station observation data, WRF (The Weather Research and Forecasting) model, radar radial wind quality control and GSI cycling assimilation are used to conduct numerical simulation research on a thunderstorm gale process in Nantong, Jiangsu Province on April 30, 2021, and compare and analyze the spatial-temporal evolution and structural characteristics of radar reflectivity, wind field and thermal dynamics simulated by different test schemes. The results show that the cycling assimilation scheme (Exp3) with assimilation intervals of 30 minutes has significantly improved the simulation results compared to the non-assimilated and non-adjacent cycling assimilation scheme, indicating that cycling assimilation and increasing the frequency effectively improve the initial field. The UNRAVEL dealiasing algorithm effectively removes velocity ambiguities and improves the initial field in the cycling assimilation scheme (Exp4) after processing radar data with dealiasing, leading to significant adjustments in the simulated radar reflectivity and surface wind fields for this thunderstorm wind event.The corresponding features and evolving trends are consistent with observations, demonstrating that the cycling assimilation scheme with UNRAVEL dealiasing is more effective in improving the initial field. From the results of the thermodynamic field, the dynamic and thermal structure of Exp4 scheme is improved more obviously, with upper-level divergence and lower-level convergence, and a "cold-warm-cold" thermodynamic structure. This structure is accompanied by strong upward motion, a north-high/south-low pressure distribution, and strong vertical wind shear, which helps to transfer horizontal momentum from the mid-high level to the near-surface layer through the sinking airflow, thereby triggering this thunderstorm wind event.
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shaoduanzhou, zhangyu, xujianjun, chensiqi, lijiajing, hujiazheng
Available online:April 24, 2023 DOI: 10.3878/j.issn.1006-9895.2301.22122
Abstract:In this study, three model perturbation schemes, the stochastically perturbed parameter scheme (SPP), stochastically perturbed physics tendency (SPPT), and multi-physics process parameterization (MP), were used to represent the model errors in the regional ensemble prediction systems (REPS). To study the effects of different model perturbation schemes on Typhoon forecasting, three sensitive experiments using three different combinations (EXP1: MP, EXP2: SPPT + SPP, and EXP3: MP + SPPT + SPP) of the model perturbation schemes were set up based on the Weather Research and Forecasting (WRF)-V4.2 model for the Typhoon "Kompasu" on the 18th of 2021. The results show that for typhoon forecasting, ensemble forecasting experiments could simulate the process of typhoon intensification and the path of typhoon, and the simulation result of EXP3 was the best. The path bias of EXP3 was the smallest of the three ensemble forecast experiments with an average value of 52.8 km, while the values of CTRL, EXP1 and EXP2 were 61.8, 54.4 and 65.7 km, respectively. For the perturbation energy, the perturbation energy of the three sets of ensemble prediction experiments were larger than the CTRL. The perturbation energy of EXP3 developed the fastest, and the perturbation energy was the largest. The Brier scores of the three sets of experiments improved the forecast results compared to the CTRL, and the Brier score values of EXP3 were the most improved of the three sets of experiments, with EXP1 and EXP2 showing improvements of 45% and 48.76% relative to the CTRL, while EXP3 was able to reach 70%. The forecasts of EXP2 and EXP1 were comparable, and EXP3 had improved the forecasts compared to EXP1 and EXP2, and its improvement rate reached 57.5% and 40% relative to EXP1 and EXP2.
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Available online:April 24, 2023 DOI: 10.3878/j.issn.1006-9895.2212.22132
Abstract:Short-wavelength radar has advantages in observing microphysical properties of cloud particles. It is a powerful device for detecting cloud —— a key member of the global water cycle. This paper briefly reviews the theoretical basis of short-wave cloud radar detection. Based on the basic principle of radar detection, with the electromagnetic scattering theory of small particles, a radar forward model (radar simulation package, RSP) is established for multi-wavelength radars and different cloud particle types. RSP is used to simulate and analyze the detection capability of three short-wave radars (X band-9.5GHz-3cm, Ka band-35GHz-8mm, W band -94GHz-3mm). Compared with the Rayleigh method, RSP method is proved to be reliable and accurate. Based on the simulation results of RSP, the power-law relationship between liquid water content (LWC) and radar reflectivity factor (Ze), effective particle radius (re) and Ze is established; a retrieval method of average LWC is also established by using Ze difference between two wavelengths at cloud base and cloud top. This paper discussed the retrieval methods of using different radar parameters to extract the microphysical parameters of liquid cloud droplets, which provides a more accurate theoretical understanding of the cloud characteristics detected by multi-wavelength radar. The RSP provides an analysis tool for the simulation of radar detection and the inversion of cloud microphysical parameters.
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Zha Sijia, Hua Shaofeng, Chen Baojun
Available online:April 24, 2023 DOI: 10.3878/j.issn.1006-9895.2212.22027
Abstract:A silver iodide (AgI) cloud-seeding parameterization has been implemented into the Thompson microphysics scheme of the WRF model to investigate cloud-seeding effects during the opening ceremony of the Nanjing 2014 Youth Olympics Games. The results showed that the surface precipitation was decreased due to seeding, and the subcloud dry layer played an important role in modifying seeding effects. The low-relative-humidity environment was favorable for rain suppression by cloud seeding, but the situation reversed in high-relative humidity environment. The seeding enhanced the formation of snow but weakened the growth of snow, especially deposition growth. As a result, the concentration of snow increased but the size of snow decreased. The snow melted and turned into a large number of small raindrops, which evaporated easily, resulting in less precipitation on the ground.
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Zhu Haoqi, Ping Fan, Tan Guirong, Shen Xinyong, Yin Lei
Available online:April 24, 2023 DOI: 10.3878/j.issn.1006-9895.2303.22213
Abstract:The Weather Research and Forecasting (WRF) model was used to simulate the hailstrom in Beijing on June 25, 2021 in this paper. From the perspective of radar reflectance and precipitation, the numerical simulation basically reproduces the macroscopic characteristics of hail storm. On this basis, the mesoscale thermal, dynamic and microphysical characteristics of hail storm in different development stages are analyzed. Finally, the mass budget and latent heat budget of hail particles and raindrops are analyzed emphatically by outputting the intermediate transformation term of the microphysical process, and the conceptual model diagram of cloud microphysics of hail formation is given. The result of research shows that: the process of hailstorm can be divided into three stages: multi-cell echo,linear convection and squall line. In this hail weather, snow particles are mainly hail embryos, which form hail particles by accretion of rain and cloud water by snow in the middle and upper troposphere, they grow by means of accretion of rain and cloud water by hail after the formation of hail particles. Production rate for accretion of rain by cloud ice or accretion of cloud ice by rain to form hail particles is very low. The airflow flows in at the front lower level of the storm, and the two weak updrafts of the multi-cell stage constantly merge. In the linear convection and squall line stage, the inflow of low layer was weakened, while the inflow of dry and cold air was obvious in the middle and high layer. The air flow rose strongly in the squall line phase and flowed forward at the upper level. When the water vapor is lifted up by the updraft and meets the cold and dry air flowing in from the middle and upper levels, it condenses into cloud water and frozen ice particles, a large amount of latent heat is released, which leads to the enhancement of buoyancy and the strong rise of the air flow in the cloud, lifting up more water vapor to condense into cloud water or ice particles and promoting the formation and accumulation of hail particles. The melting of snow and hail particles absorbs large amounts of latent heat, causing the melting layer to rise. Therefore, a large number of supercooled rain form in the squall line stage, which increase production rate for accretion of rain by snow to form more hail particles. The lower level downdraft will be enhanced by the stronger drag of water material caused by the fall of large hail particles. Downdraft causes evaporation of rain water at lower levels, forming cold pools near the surface by cooling effect , which cooperate with latent heat heating at higher levels to enhance convection. Thus, it positively feeds back to the meridional circulation. The vertical updraft caused by the circulation promotes water vapor in the lower layers to rise above the melt layer and condense into supercooled water and snow particles, while the vertical downdraft promotes snow and hail to melt into rain water and rain water to evaporate below the melt layer, and then positively feeds back to the thermal environment within the cloud. This repetition produced hail and heavy precipitation.
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Available online:April 24, 2023 DOI: 10.3878/j.issn.1006-9895.2302.22246
Abstract:In this study, Typhoon Maysak (No. 09) in 2020 is numerically simulated using the WRF4.2, which replicates the transitional process and torrential rain caused by the gradual interaction of Maysak with the cold trough during its northward motion.The influence and mechanism of the cold trough on the spatial distribution and temporal variation of precipitation intensity are obtained by analyzing the thermodynamic, dynamical, and cloud microphysical characteristics of the typhoon"s eyewall and rainband areas. (1) The typhoon"s eyewall is invaded by dry and cold air from the middle atmosphere, which lowers the height of convection. The intrusion forms an unstable structure with a dry upper layer and a moist lower layer that favors the maintenance of convective intensity in the lower and middle atmosphere.In the rainband of typhoon, the importance of vertical vorticity transfer, as well as cold air invasion from lower atmosphere to lift warm air, enhances the upward motion of the middle and upper atmosphere. (2) The main cloud microphysical processes of this precipitation are as follows: the snow that comes from water vapor desublimation absorbs cloud water as it falls and melts into rainwater, which in turn collects a significant amount of cloud water, causing the rainwater to increase. There is also a part of rainwater originated from the melting of graupel and rainwater collected graupel , and graupel primarily produced by the process of cloud water collected by snow.(3) By changing the typhoon"s thermodynamic structure, the cold trough influences the spatial distribution of cloud water and snow, which in turn determines the spatial distribution of precipitation: Cloud water gathers toward the core in the eyewall , whereas snow is ahead of cloud water in the rainband along the direction of outflow. And rainwater is primarily distributed in areas where a certain amounts of snow and cloud water overlap.In terms of quantitative characteristics, the invasion of cold and dry air increases the efficiency of snow desublimation and rainwater evaporation in the rainband while decreasing the efficiency of cloud condensation, resulting in a higher proportion of snow and a lower proportion of cloud water and rainwater of the hydrometeors in the rainband. (4) The cold trough directly affects the efficiency of snow desublimation and cloud water condensation by changing the vertical velocity of the typhoon, which then tends to affect the efficiency of the processes of snow collecting cloud water, snow collecting cloud water converted into graupel, snow melting to rainwater, rainwater collecting cloud water, graupel melting to rainwater, and finally leads to the change of precipitation.
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LIU Longsheng, LIU Lian, HUANG Bin
Available online:April 24, 2023 DOI: 10.3878/j.issn.1006-9895.2303.22136
Abstract:Caused by an extratropical cyclone across the Yellow Sea, a large-scale sea fog event from March 27 to 28, 2021 was investigated using the ERA5 reanalysis data with the spatial resolution of 0.25° × 0.25°, ground observation data of China Meteorological Administration, satellite retrieval data and the WRF model. Results are as follows: (1) The air-sea temperature difference is between 0.5 ℃ and 2 ℃ in the initiation and the difference is negative in the mature stage of sea fog. (2) The moist air convergence from the extratropical cyclone provides the water vapor source for the formation and maintenance of the sea fog. The southwest warm and moist air flow transported by the low-level jet promotes the establishment of the inversion layer. (3) The "double inversion" appears in the Yellow Sea. The inversion layer in the low level is caused by the warm advection of the low-level jet, while in the high level is caused by the sinking and warming of the dry and cold air behind the extratropical cyclone. (4) Under the synergetic effect of the extratropical cyclone and the low-level jet, the atmospheric turbulent kinetic energy increases in the near sea surface boundary layer. This also promotes the development of the sea fog in the vertical direction.
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Liu Jing, Liu Zhaoxu, Zhou Yaman
Available online:March 31, 2023 DOI: 10.3878/j.issn.1006-9895.2212.22097
Abstract:Combined with the ground-based GPS-MET observation data and the HYSPLIT trajectory model based on the Lagrange method, the large-scale water vapor transport, convergence characteristics and water vapor source during a persistent heavy rainstorm event on the Northern Slope of the Middle Kunlun Mountains were analyzed. The relationship between large-scale circulation anomaly and water vapor continuous relay transport during heavy rainfall in arid area was clarified. The result showed：(1) Before the precipitation, the location of the subtropical high was abnormally westward, and the southward airflow on the periphery of the subtropical high caused obvious humidification over the Tibet Plateau. During the heavy rainfall, the subtropical high stretched to the northwest, and the water vapor from low latitude was conveyed to heavy rainfall area along the Indian summer monsoon circulation and Tibet plateau, gather with the south airflow in front of Tashkent low vortex,which constituted the water vapor transport channel for this heavy rainstorm, and resulted two sharply humidification over heavy rainstorm station. The peak PWV of the station is nearly two times of the climatic average. (2) the temperature anomaly at 300 hPa played an important role in the water vapor transport for this heavy rainstorm. Before and during heavy rainstorm, the 300 hPa warm anomaly center excited the 200 hPa anticyclonic circulation anomaly center and meridional wind positive anomaly center. Meanwhile, the 500 hPa anticyclonic circulation anomaly center and cyclonic circulation anomaly center were excited in the south and west of the warm anomaly center (north of the Indian Peninsula). At the back of the anticyclonic circulation at 500 hPa, the warm and wet air was transported northward along the positive windward anomaly center at the low latitude, and converged with the southerly air from the east of the cyclonic circulation in the rainstorm area, providing abundant water vapor supply for the persistent rainstorm.
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Yang Qianyuan, Zhang Wancheng, 闵颖, 朱莉
Available online:March 31, 2023 DOI: 10.3878/j.issn.1006-9895.2302.22022
Abstract:Using the observation data and NCEP/NCAR reanalysis data, The characteristics of Plateau vortex shear in summer during 2008-2012, which moved southeastward to Yunnan Province resulting in heavy precipitation, are analyzed. The results show that these events are mainly divided into three types: the strong cold air behind plateau vortex shear, the supplementary of plateau vortex shear and the weakening southeastward plateau vortex shear. Among them, the third type produced the most of heavy rain in Yunnan. North-central Yunnan is the main area of heavy rain and the typical affected area of Plateau vortex shear in Yunnan, the rainfall in these areas mainly occurs at night. The first type has the largest influence area, which can cause rainstorm in whole province, but has less frequent. During the second and third type of events, the high (ridge) between Yunnan and Myanmar are maintained. Precipitation area and are related to the location of subtropical high、the meridionality of vortex shear and the time. There is obvious income of water vapor in Yunnan during the heavy rain; The meridional moisture income is stronger than the zonal moisture output. By using HYSPLIT model, the water vapor transportation of rainstorm are analyzed. The Bay of Bengal is the most important water vapor source. In north Yunnan, the contribution of water vapor from plateau is important. Some moisture over the Tibetan Plateau comes from the region to the Arabian Sea, the others from the Bay of Bengal. During the process of transport, every air flow might experience several periods of evaporation-precipitation in which it was influenced by terrain.
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zengxiaoqing, caoyong, wangyu, GUO Yunqian
Available online:March 31, 2023 DOI: 10.3878/j.issn.1006-9895.2302.22104
Abstract:With the continuous development of higher resolution and more accuracy grid forecasting operation, the spatial and temporal accuracy and precision of grid forecast products need to be continuously improved. To maintain the compatibility between grid and site forecast , a fast refinement interpolation (FRI) method which takes into account both the static real terrain and the dynamic atmospheric vertical variation process was investigated. In this study, 3-36h forecast products for three models (ECMWF, CMA-GFS and CMA-MESO) from January 1, 2022 to March 31, 2022 were selected as experimental data. Individual weather process tests, FRI parameter selection tests and long-term interpolation test comparisons were conducted. From long-term interpolation tests and individual case trials, the FRI method has a clear advantage over the bilinear interpolation method. From the spatial perspective, the FRI method can improve the spatial interpolation accuracy of 2m temperature above the ground and the results are more consistent with the topographic variation. From a temporal perspective, the FRI method has significantly improved the accuracy of the 2m temperature interpolation results compared to the bilinear interpolation method, especially in the western region with complex subsurface. The loss parameter in the method can also be used as an indicator to check the 3D atmospheric vertical variability of the model product. The FRI method is fast and efficient and has a clear physical meaning, which provides an important theoretical support for more accurate reflection of near-surface meteorological forecast information.
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Air mass budget at iso-moist-static-energy levels during the super long-lasting Meiyu in summer 2020
MIAO Yujie, YU Yueyue, CHEN Gang, GUAN Zhaoyong, LI Xichen
Available online:March 30, 2023 DOI: 10.3878/j.issn.1006-9895.2211.2144
Abstract:Using the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis dataset from 1980 to 2020, the iso-Moist Static Energy (iso-MSE) mass circulation analysis is conducted to investigate the characteristics of air mass and mass fluxes at various iso-MSE levels and their relationship with precipitation during the 2020 super long-lasting Meiyu. Results show that during the super long-lasting Meiyu season in 2020, air mass generally rose to higher iso-MSE levels from the tropics to the midlatitudes. The most remarkable mass gain/loss of air was found in the iso-MSE layer of 345–350KJ/335–340KJ. Significant positive/negative simultaneous correlations between air mass anomalies in the iso-MSE layer of 345–350KJ/335–340KJ and the regional-averaged precipitation anomalies over the Meiyu region has also been found, indicating that the MSE changes in the range of 335–350KJ are critical to the Meiyu season. The convergence of high energy air from tropical Indian Ocean and tropical western Pacific to the Meiyu region is an important contributor to the abnormal Meiyu, while abnormally strong local statistic instability was not found. The adiabatic mass flux anomalies in the 340–345KJ/345–350KJ layer over the Meiyu region, which dominantly resulted in daily changes of iso-MSE mass, are negatively/positively correlated with the precipitation at a lead time of 1–2 days. The features of iso-MSE mass flux anomalies and the relative importance of its meridional and zonal components in the period before heavy precipitation vary at different stages of Meiyu season. Particularly, near the onset of the Meiyu season, anomalous mass gain with the MSE of 345–350KJ in the Meiyu region was mainly contributed from the anomalous meridional mass flux, which preceded the heavy precipitation by 1 day. At the end of the Meiyu season, anomalous mass loss with the MSE of 340–345KJ was mainly contributed from the anomalous zonal mass flux around 2 days prior to the variation of precipitation. Such anomalous signals in the iso-MSE mass circulation can be potentially useful precursors for the onset/end date of Meiyu season from the perspective of moist static energy.
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Available online:March 30, 2023 DOI: 10.3878/j.issn.1006-9895.2210.22043
Abstract:Based on the CINRAD/SA radar observations in Beijing and Tianjin, the radar echo evolution characteristics of two convective cells A and B in a severe convective storm affecting Beijing on June 30, 2021 are analyzed. Through the analysis of the variation of various physical parameters and the number of grid points of different reflectivity intensity grades in different stages of cell development and before and after operation in the statistical area. The evolution characteristics of cells with different strengths under different operating conditions are obtained. The results show that the cell B is a normal convective cloud cluster (life time is 3 hours), and after the large dose operation (74 rockets and 58 anti-aircraft guns are effectively operated within 24 minutes) in the early stage of development, it can be seen that the cell B has good characteristics of inhibiting the development of the cell. The parameters such as mean reflectivity, storm body height and vertically integrated liquid water at different heights of the storm body all show a downward trend. The number of grid points of the stronger echo (30-60dBZ) decreases, while the number of grid points of the weaker echo (20-30dBZ) increases rapidly, and the convection structure weakens as a whole. Cell A is a supercell (life time is 5.5 hours), and there is no obvious inhibition effect in the initial stage due to insufficient operating dose (15 rockets are effectively operated within 30 minutes). Near the mature stage, continuous high-dose operations were carried out (105 rockets and 182 anti-aircraft guns were effectively operated within 80 minutes). Although some characteristics similar to echo B can also be observed: the average reflectivity, cloud top height, strong echo thickness, vertical integrated liquid water and other parameters in the upper layer decrease, the number of grid points in the higher reflectivity intensity range (50-70dBZ) decreases, and the number of grid points in the lower reflectivity intensity range (30-50dBZ range) increases and lasts for about 30 minutes. However, the overall work suppression effect on supercell A is not obvious.
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XU Liren, CAI Jun, LI Yupeng, PING Fan, LI Ji
Available online:March 30, 2023 DOI: 10.3878/j.issn.1006-9895.2302.22176
Abstract:The WRF 4.2 (Weather Research and Forecasting) mesoscale numerical weather prediction model was used to simulate a heavy snowfall in Beijing from February 12 to 13, 2022, and the spatial and temporal evolution characteristics of the snowfall were well reproduced. Based on the simulation data, the differences in dynamic, thermal and cloud microphysical processes between the northern mountainous area and the southern plain area were analyzed, and the possible impact of complex terrain on the snowfall process was discussed. The precipitation particles are ice phase particles. At the same time, there was significant conditional symmetry instability in the atmosphere. The simulation results show that precipitation in mountain areas was stronger than that in plain areas. The comparison of dynamic and thermal conditions between the mountainous area and plain area shows that the divergence field and vorticity field in the mountainous area were stronger due to the existence of topography. The vertical velocity was higher than that in the plain area, and the perturbation potential temperature was stronger. The cloud developed more vigorously over the mountainous area, and there were dominant water vapor sink areas over the mountainous area, and the phase transition process of water vapor is more active. Although ice crystals and snow were the main hydrometeor particles in mountain areas and plain areas, the content of ice crystals and snow was high in the mountain area. The dominant conversion processes of ice crystals in the cloud included nucleation of ice crystals, deposition of ice crystals, automatic conversion of ice crystals to snow, accretion of ice crystals by snow, deposition of snow crystals, and sublimation of ice crystals and snow crystals near the surface. The difference in water vapor conditions near the surface made the sublimation process of ice crystals and snow stronger in plain areas. In addition, the occurrence of supercooled cloud water generated by the activation of cloud droplets near the near-surface layer below 1.5 km altitude promotes the deposition of ice crystals and snow, and the accretion of cloud water by snow.
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Available online:March 30, 2023 DOI: 10.3878/j.issn.1006-9895.2302.22204
Abstract:Single sea surface wind data has problems such as few observations, uneven distribution or difficulty in covering the earth. Multi source wind data are used for fusion to achieve grid continuity, which can effectively cover the sea surface and improve operational accuracy. Four kinds of sea surface wind data were collected: buoy, ship report, ASCAT scatterometer and China-France Oceanography satellite scatterometer (CSCAT) wind data. Firstly, the quality of CSCAT wind data was compared and verified, and then the time-space weighted interpolation method and the optimal interpolation method were used. With CSCAT data as the core, supplemented by other wind data, the daily average global wind fusion and 3-hour regional wind fusion were carried out, and then the quality of the fusion wind was inspected. The results show that the accuracy and stability of CSCAT data are slightly lower than that of ASCAT data; The wind field after the fusion of two kinds of data can meet certain operational accuracy requirements. This method is simple to implement, and the fusion data is reliable. Especially in the sparsely observed area, it can provide some reference for quickly obtaining the high resolution sea surface standard and grid wind field.
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Available online:March 30, 2023 DOI: 10.3878/j.issn.1006-9895.2303.22203
Abstract:Eurasian snow cover is an important factor affecting the climate in the mid-high latitudes. A deep understanding of the characteristics and causes of Eurasian snow cover abnormal changes is of great significance for climate research and improvement of climate prediction. The current research focuses more on the interannual and interdecadal changes and climate effects of snow cover, while it is obviously insufficient for the understanding of the intraseasonal changes of snow cover. Based on the observation and reanalysis data, this paper discusses the intraseasonal variation of spring snowmelt in different regions of Eurasia continent and its related atmospheric circulation characteristics and surface energy evolution process through statistical diagnosis. The results show that the Eurasian spring snowmelt anomaly has obvious intraseasonal variation, with the dominant cycle of 10-30 days, and the intraseasonal signals mainly appear in the Scandinavian Peninsula, the Eastern European Plain and Western Siberia. Further analysis shows that the intraseasonal variation of snowmelt in Scandinavia may be related to the Scandinavian teleconnection negative phase (SCA-), and the intraseasonal variation of snowmelt in the Eastern European plain may be related to the Eurasian teleconnection negative phase (EU-). The intraseasonal variation of snowmelt in West Siberia may be related to Scandinavian teleconnection positive phase (SCA+). There are obvious differences in the causes of snowmelt anomalies in different regions. The increase of long-wave radiation may be the main cause of snowmelt anomalies in Scandinavia. In the East European plain and West Siberian region, sensible heat flux anomalies may be the main cause of snowmelt anomalies.
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Available online:March 15, 2023 DOI: 10.3878/j.issn.1006-9895.2210.22207
Abstract:The comprehensive observational analysis of the Northeast cold vortex (NECV) rainstorm that occurred in Liaoning and Jilin provinces on June 2-3, 2021 was?investigated?using multi-source observations and reanalysis data, and then a high-resolution numerical simulation of main precipitation period produced by the WRF, combined with three dimensional precipitation diagnostic equations, to carry out a diagnostic study of the macro and micro physical processes and the mechanism of rainfall. The results show that the precipitation was widespread, with strong local rainfall and prominent convection. During the rainstorm, the East-Asian atmospheric circulation was relatively stable, the NECV moved slowly eastward, carrying cold air southward and converging with southerly warm-wet airflow, which in turn triggered the development of a vortex cloud system. The two provinces were located to the left outlet of the high-level jet and to the front of the low-level jet, the dynamical structure of high-level dispersion and low-level convergence contributed to the development of precipitation. The intensification of vapour convergence was accompanied by the vigorous development of cloud physical processes and a significant increase in water species, of which graupel made an important contribution to precipitation through cloud physical processes such as melting into raindrops. Cloud droplets grew rapidly through vapour condensation and were consumed largely during cloud microphysical transformations for cloud system development and precipitation. Precipitation intensity was influenced by a combination of vapour and cloud budget. In the early stage of precipitation, along with a significant increase in vapour transport and convergence, the local vapour content increased and precipitation systems developed. Later, the local convergence weakened as the cold vortex cloud system gradually moved eastwards, the local vapour depletion continued to support heavy precipitation; Exuberant development of water species (especially ice-phase) accompanied local vapour convergence. In early stage, the rapid development of precipitation clouds were supported by a combination of liquid-phase hydrometeors convergence and microphysical transformation processes. The above two processes remained active at the peak of the precipitation, but local change of hydrometeors was not obvious due to the depletion of heavy precipitation. The liquid hydrometeors continued to converge throughout the storm, while the ice hydrometeors gradually turned into weak divergence after a short period of convergence at beginning, this evolutionary feature was related to local thermal and dynamical structure and their evolution.
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Available online:March 15, 2023 DOI: 10.3878/j.issn.1006-9895.2210.22202
Abstract:In this paper, we firstly analyze the moisture transport and convergence characteristics of an early summer cold vortex rainstorm in Northeast China using the traditional Eulerian method, then use a Lagrangian particle dispersion model FLEXPART and quantification of the contribution from moisture sources to reveal the sources of moisture and their contributions to this rainstorm process. The results show that during this early summer northeast cold vortex (NECV) rainstorm, the subtropical high pressure positioned to south, and the northeast region was mainly influenced by the NECV and the weak high-pressure ridge in the Japan Sea downstream of it. In lower troposphere, the cyclonic flow between the subtropical high and the weak high-pressure ridge in the Japan Sea contributed to a low-level jet northward along the coastal areas of China, it was conducive to the northward transport moisture from the south of the Northeast China, which intersected with cold-dry airflow from the rear of the NECV in Liaoning and Jilin provinces, triggering heavy precipitation. Lagrangian trajectory tracking showed that more than 60% of the target air masses came from the Eurasian continental region to the west and northwest of the precipitation area, their initial position were high, and when they passed through East China Sea and Yellow Sea, the height decreased significantly and merged into the southward warm-wet airflow, which then flowed into target precipitation area; The other part of air masses came from Lake Baikal and its eastern region, as well as the South China Sea and the south-central continental region of China, the air masses were at a lower height in both its initial position and during its travel. The quantitative contribution of moisture from the source regions to the target regions showed that region D (East China Sea-Yellow Sea to Northwest Pacific) made the largest contribution (37.04%), followed by region C (East-Central China) (30.05%), with significant moisture uptake and low loss along the way, making the contribution of moisture from these two regions significant. While the contribution of moisture uptake from the local precipitation area ranked third. In addition, Lake Baikal and the area east of it (region B) and central-western Eurasia (region A) also contributed (although the great total moisture uptake in region A , most of it was lost during long-distance transport), while region E (the Indian peninsula to the South China Sea) made the smallest moisture contribution, which showed that the moisture of NECV rainstorm in early summer was less likely to be supplied from low latitudes. The Lagrangian method gave a clearer picture of the main sources of moisture and their contribution to the rainstorm process than the traditional Eulerian method.
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LuoLinjie, TanYongbo, ZhengTianxue
Available online:March 15, 2023 DOI: 10.3878/j.issn.1006-9895.2209.22078
Abstract:A large number of studies based on observation have proposed that the extension scale of lightning channels is closely related to the charge distribution pattern, and these small and frequent lightning in the strong convection area is likely to be formed in the pattern of charge pockets. In order to verify that such cloud flashes can be formed under the background of pocket charge, and give the general law of lightning initiation and discharge under this charge distribution pattern, in this study, the lightning discharge parameterization scheme was coupled into the double-layer uniform pocket charge model, and a large number of random simulation tests were carried out. The total dimension of the charge region was fixed while changing the pairs of charge region in the simulation process to discuss the similarities and differences of lightning initiation and discharge behavior under each charge background. Simulation results indicate that (1) With the increase of charge pairs, the charge concentration and the total charge quantity for lightning start-up both increase. (2) The axial?ratio of each small charge region is the key factor affecting the lightning initiation behavior. In addition, the spatial configuration relationship of multiple pairs of charges and the runaway breakdown threshold, these two?key?factors also make the lightning starting position and probability different in the horizontal and vertical directions in each case. (3) The spatial characteristics of lightning are limited by the geometric characteristics of small charge region. (4) Besides, the distribution of charge region significantly affects the development shape of lightning. Under each charge background, the distribution range and concentration area of initial leader angle are different. Compared with the previous charge structure(flat ellipse), when the vertical and horizontal radius of the small charge region are equal, the variation range of initial leader angle is significantly increased, and the number of horizontal development cases is significantly increased.
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Available online:March 15, 2023 DOI: 10.3878/j.issn.1006-9895.2211.22099
Abstract:Faithful simulation of the Madden-Julian Oscillation (MJO) can significantly improve extended-range prediction, but the numerical models have difficulty in simulating the MJO. One of the main challenges is how to simulate the MJO propagation speed properly. In this study, we examine the propagation speed of MJO during boreal winter in CMIP6 models and reveal the key factors controlling the MJO propagation speed in models. The result shows that most of CMIP6 models can well simulate the MJO’s eastward propagation over Indo-Pacific warm pool, but the simulated MJOs in different models have diverse propagation speeds. It is shown that the Kelvin-wave response and Rossby-wave response to the MJO heating are the key circulation factors affecting the simulated MJO propagation speed, with stronger Kelvin-wave response and weaker Rossby-wave response corresponding to faster propagation. The variation of the MJO circulation structure among models is attributed to the diverse background sea surface temperature (SST). The models simulating faster MJO tend to have higher SST over Central Pacific (CP) and Western North Pacific (WNP). The warming over CP affects the MJO speed in two ways. First, this zonal expansion of the warm pool can increase the MJO horizontal scale, leading to stronger Kelvin-wave response that favors faster MJO propagation. Second, it increases the moisture content over CP, which weakens zonal moisture gradient over West Pacific, resulting in acceleration of the MJO through enhancing the zonal moisture advection. Different from previous studies, we find that the SST warming over WNP also affects the MJO speed. The SST warming over WNP leads to a more symmetrical SST distribution about the equator, which enhances the moisture content over Maritime Continent, leading to more equatorial symmetric distribution of the background specific humidity during boreal winter. This symmetric distribution of moisture is conducive to the development of Kelvin wave response. The results here not only have implications in understanding the MJO dynamics, but also indicate that realistic simulation of MJO requires fidelity in simulation of background states.
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Lingxiao JI, Yansong BAO, Yuan WEN, Huan LI, Jiali DING
Available online:March 15, 2023 DOI: 10.3878/j.issn.1006-9895.2211.22049
Abstract:In order to evaluate the impact of spaceborne lidar product data assimilation on typhoon forecast, this paper studied the assimilation of Aeolus Horizontal line-of-sight data and its impact on typhoon forecast for Typhoon Hagupit in 2020 and Typhoon Lekima in 2019. First, we conducted statistical test and deviation correction on Aeolus products and used the statistical root meean square error of each hight layer as the observation error for the assimilation. Then, Aeolus products were assimilated by WRFDA (Weather Research and Forecast Model Data Assimilation) model, and the prediction test was carried out by WRF (Weather Research and Forecast Model) model. The experiment results show that the Aeolus products are highly accurate, the observation error of each layer after correction is in the range of 3-5 m/s and increases with the increase of height. The corrected data meet the unbiased assumption of three-dimensional variational assimilation. Assimilating Aeolus products during Typhoon Hagupit and Typhoon Lekima can make the model show more reasonable circulation patter and effectively improve the track and intensity forecast of typhoon Hagupit and Lekima.
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Available online:March 13, 2023 DOI: 10.3878/j.issn.1006-9895.2301.22181
Abstract:With the development of wind power utilization, more and more wind farms are built in the mountainous areas of complex terrain. In order to better conduct wind energy assessment and wind power forecast, it is necessary to understand the impact of complex terrain on the wind speed profile. Based on the thin airfoil theory and the linearization theory of the disturbance of turbulent boundary layer, the paper predicts the wind profile in the two-dimensional cross section using two-layer model. It can accurately predict the influence of terrain, pressure, stability on the growth of wind speed. bBut for the three-dimensional terrain or other factors, the model needs to be further extended to three dimensions, and combined with numerical simulation.
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Chen Zhen-xuan, Chen Ke-yi, Xian Zhi-peng, Xi Shuang
Available online:March 01, 2023 DOI: 10.3878/j.issn.1006-9895.2302.22085
Abstract:With the successful launch of FengYun-3, more satellite observations of radiances are directly assimilated. The satellite microwave all-sky assimilation technology can make better use of the microwave observation data in clear, cloudy and precipitating conditions. It can not only increase assimilated radiances, but also show positive impacts on numerical weather prediction. As a result, the all-sky approach gets a lot of attention now. In this study, a typhoon case called Maria in July 2018 is selected and all-sky assimilation of FY-3C/MWHS-2 data were used in Weather Research and Forecasting Model, based on the 3-dimensional variational data assimilation technique within the WRFDA (WRF data assimilation) system, in order to study the impacts of assimilating FY-3C/MWHS-2 data under the all-sky conditions and using different data types of the initial fields on the forecasts in the regional numerical model. The comparison of the clear-sky and all-sky assimilation experiments shows that under the all-sky conditions, more clouds and precipitation data are assimilated and the data usage is increased. Improvements are displayed in the analysis of the vertical structures of Maria, such as the warm core and the symmetric wind speed structures, and the humidity fields. The average reduction rates of the track error are about 34% to 62%. These positive impacts can be demonstrated in all the all-sky experiments with different data types for initializing WRF.
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CHEN Yixin, DU Rongguang, ZHANG Dianguo, TENG Xiaomi, WANG Yue, LIU Lei, XU Liang, WANG Wenqing, XIE Jun, QI Bing, FANG Shuangxi, LI Weijun
Available online:February 28, 2023 DOI: 10.3878/j.issn.1006-9895.2301.22071
Abstract:The process of aerosol-cloud interaction is essential for assessing the lifetime of cloud and aerosol as well as the climate effect. The current study on aerosol-cloud interaction was mainly based on satellite retrieval data and modeling simulation, while field observation was less carried out due to difficult deployment, long experimental duration, and facilities and labor consuming. Therefore, the aerosol-cloud observational data from field campaigns become significantly important. In this article, we took a field study of clouds and aerosols at a high mountain station in the Yangtze River Delta, employing fog monitor, ground-based counterflow virtual impactor, scanning mobility particle sizer and so on. The study investigated the characteristics of cloud droplets and aerosols at the mountaintop of Mt. Daming (1483 m a.s.l.) during cloudy period in July, 2021 to discuss the impacts of aerosols on the formation and development of clouds and the scavenging effect of cloud on aerosols. The removal rate is about 20%~50% at the initial stage of cloud formation, and the higher supersaturation of atmospheric water vapor and the larger aerosol particle size, the higher the removal rate. The result indicated that particles with larger size are more inclined to activate into cloud condensation nuclei. By comparing three different stages with various aerosol abundance in a same cloud event, we discovered that low aerosol load was advantageous for the formation of thick clouds with high liquid water content, and the cloud was composed of droplets with larger size but relatively less number. In contrast, the increasing aerosol particles might lead to the thin cloud composed of plenty of small droplets. Moreover, we further analyzed the size distribution of dry residual nuclei of cloud droplets with size > 8 μm. The result showed that the cloud condensation nuclei of these large cloud droplets were mostly formed by aerosol particles with size > 100 nm. Following the higher number concentration of aerosol particles in same cloud, the number of cloud droplets with size > 8 μm significantly decreased and the diameter of cloud condensation nuclei became larger. These results indicated that the number enhancement of aerosol particles can increase the number of cloud droplets and reduce the droplet diameter. Meanwhile, the critical activation diameter of aerosol particles become larger in the water-limited cloud. Therefore, we concluded that size distribution of aerosol particles influenced number and diameter of cloud droplets, conversely, the formation and development of cloud had a certain scavenging effect on aerosols.
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Available online:February 24, 2023 DOI: 10.3878/j.issn.1006-9895.2211.22166
Abstract:A series of abrupt events of Asian monsoon occurred in the Holocene, of which the 9.2 ka BP event has received less attention, and its existence and genetic mechanism are still controversial. Based on the Community Earth System Model (CESM), this study has carried out the transient integral climate simulation test (Nanjing Normal University-12ka, NNU-12ka) since the Holocene, compared the reconstruction data with the Transient Climate Evolution over the last 21,000 years (TraCE-21ka), and explored the spatial and temporal characteristics of the 9.2 ka Asian weak monsoon event and its causes. The main progress is as follows: the solar activity sensitivity test of NNU-12ka presents the Asian weak monsoon event around 9.6-9.4 ka, at this time, the total solar radiation decreased by 0.38 W m-2, and the average summer precipitation in the Asian monsoon region decreased by 0.17 mm day-1. However, the results of the total forcing test based on TraCE-21ka show that the glacier melt water and the ice cover change have no significant impact on the Asian monsoon change in this period. In the NNU-12ka solar activity test, the summer precipitation in the Asian tropical monsoon region decreased significantly, and the precipitation in Northeast China increased slightly. The reason for the weakening of the tropical monsoon is that the sudden drop of solar radiation leads to the weakening of thermal difference between the land and the sea, strengthens the sea level pressure of Asia"s land, causes the abnormal subsidence movement of the tropical monsoon region, suppresses the transmission of water vapor to the Asian monsoon region, and then weakens the monsoon through dynamic process.
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Available online:February 24, 2023 DOI: 10.3878/j.issn.1006-9895.2210.22126
Abstract:Using the precipitation derived by the CPC MORPHing technique (CMORPH) of the US National Oceanic and Atmospheric Administration (NOAA), the US National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 reanalysis (CFSv2), ERA-5 reanalysis obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF), and the Madden-Julian Oscillation (MJO) index of Wheeler and Hendon, effects of MJO on the rainfall persistence over eastern China in the summer of 2020 were analyzed. Based on the analyses of correlation, regression and wave source, three major conclusions were obtained as follows. 1) Compared with rainfall of the previous 21 years, the summer precipitation over eastern China in 2020 was extremely strong. This is because the summer monsoon rain belt has maintained for a very long time over southern China and the middle and lower reaches of the Yangtze River during 2020. 2) Meanwhile, a negative geopotential height anomaly in the middle and upper atmosphere, with the water vapor convergence between 1000-300 hPa and the instability at the lower levels, maintained over eastern China. Thus, the atmospheric circulation was in favor of the prolonged rainfall in the 2020 summer. 3) During this period, MJO was abnormally active in its phases 1 and 2 with significant period on 10-30 days, which indicates that MJO convective centers were sustained over eastern Africa and western Indian Ocean. Therefore, significant Rossby wave sources were found over eastern Africa and western Indian Ocean, which is consistent with the Gill mode. Finally, a Rossby wave train was excited at the sources and transported by the jet stream, and then induced the negative geopotential height anomaly over eastern China. Due to the sustain of the MJO in its phases 1 and 2, the negative geopotential height anomaly over eastern maintained and prolonged the rainfall in this region during 2020. The sensitivity experiments further prove that the 10-30-day signal is in favor of the formation of the negative anomaly of 500-hPa geopotential height and the positive anomaly of precipitation over eastern China.
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YANG Zhenjiang, LI Ke, LIAO Hong, CHEN Lei
Available online:February 22, 2023 DOI: 10.3878/j.issn.1006-9895.2302.22211
Abstract:In this study, we analyze surface ozone (O3) pollution and its dominant meteorological drivers in China amid the record summertime extreme heat of 2022, using the Chinese national air quality network measurements and EAR5 reanalysis meteorological fields. Spatially, O3 concentration in China holds a high level in summer of 2022, with strong positive anomalies over northern China in June and over southern China in July-August. For long-term trend, O3 concentration in North China Plain (NCP) in June 2022 was the second highest among June months since 2015, resulting in the regionally-averaged ozone exceedance days of 21 days. In July-August 2022, O3 concentration was the highest for the same months since 2015 both for the Yangtze River Delta (YRD) and the Sichuan Basin (SCB). In terms of ozone precursor changes, relative to 2019-2021, there was only slight change in satellite NO2 columns in 2022 and the enhancement in satellite HCHO over southern China is consistent with temperature change, suggesting that the record summertime extreme heat of 2022 is the dominant driver of the O3 enhancement. Specifically, the spatial correlation coefficients between O3 and temperature anomalies in 2022 are 0.71, 0.64 and 0.49 for June, July, and August, respectively, and the O3 sensitivity to temperature in major clusters is also relatively high. This enhancement of O3 concentration also has a strong spatiotemporal consistency with the stagnant weather conditions featuring high temperature and low humidity under the control of the subtropical high. In particular, the O3-temperature relationship in 2022 is quite different from the previous years. As observed in 2019-2021, the strong positive correlation of O3-temperature is suppressed when reaching a high temperature threshold, but the positive correlation still persisted at extremely higher temperatures in 2022 in the NCP and YRD. This study highlights the importance role of extreme high temperature events on O3 pollution, which poses a pressing challenge to the synergistic control of complex air pollution in China.
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Available online:February 22, 2023 DOI: 10.3878/j.issn.1006-9895.2302.22128
Abstract:As one of the essential variables in the ocean, sea surface temperature (SST) significantly impacts global climate and marine ecology, so it is necessary to forecast the sea surface temperature. Deep learning is highly efficient at data processing, but it is rarely used in equatorial Pacific SST short-term forecasting. Based on Long Short-term Memory (LSTM) network, this paper constructs a daily forecast model of SST in the tropical Pacific Ocean (10°S-10°N, 120.0°E-280°E) in the next ten days. Using observations from 1982-2010 as a train set and data from 2011-2020 as preliminary values, the model forecasts the SST. The results show that the forecast Root Mean Square Error (RMSE) in the eastern equatorial Pacific region is more significant than that in the central and western areas. The RMSE of the east part is about 0.6°C on the first day of the forecast, while the west and central regions are less than 0.3°C. In different interannual variation phases, RMSE is the largest in the La Ni?a period, followed by normal years, and the smallest in the El Ni?o period. RMSE in the La Ni?a period is more than 20% in some regions than in the El Ni?o period. The forecast deviation is positive in the east and negative in the west. Regarding relevant forecasting techniques, the central part is the best. The number of predictable days is more than ten days. Specifically, the number of predictable days near the equatorial cold tongue is 4-7 days, and the number of predictable days in parts of the western equator is three days. Forecasting models generally have lower monthly fore-casting skills than the western regions in the eastern equatorial Pacific region, and the areas performed the worst in October and November. In general, the SST forecast model based on LSTM can well capture the evolution characteristics of SST in time series, and the forecast performance is good in different cases. At the same time, the forecast model relying on data-driven can quickly and well predict the short-term change of daily average SST within the next ten days.
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Available online:February 20, 2023 DOI: 10.3878/j.issn.1006-9895.2211.22133
Abstract:In order to study the influence of dust aerosol layer on cloud and precipitation, this paper simulated a convective process in Aksu, Xinjiang, using the Weather Research and Forecasting (WRF) high-resolution Weather model coupled with a spectral bin microphysics (SBM) scheme. The effects of the aerosol layer on cloud dynamic , microphysics and precipitation processes at different heights are discussed respectively. The results show that when the dust aerosol is in the lower layer, cloud condensation nuclei (CCN) has a more obvious effect on the cloud microphysical process. As CCN increases, cloud droplet concentration increases, cloud droplet effective radius decreases, and precipitation delays. When the dust aerosol is higher, ice nuclei (IN) has a more obvious influence on the cloud microphysical process. With the increase of IN concentration, the number of ice crystals increases, the growth process of snow, graupel and hail is enhanced, the number of ice particles involved in the melting process increases, and the rainrate increases. This article only discusses the possible response of dust aerosol layer on the convective weather process that occurred in Xinjiang at different heights,and it is necessary for more simulation study which constrained by observation data to learn the comprehensive understanding of the influence of dust aerosol on different types of cloud and precipitation process.
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Available online:February 07, 2023 DOI: 10.3878/j.issn.1006-9895.2210.22079
Abstract:The onset of the South China Sea summer monsoon (SCSSM) marks the comprehensive establishment of the East Asian summer monsoon, which is crucial for the rainy season in China. The present study compares the climatological features and interannual variability of the SCSSM onset between the JRA-55, ERA5, CRA-40, and NCEP1 reanalysis datasets. The result shows that atmospheric circulation and precipitation evolution are consistent among the four reanalysis datasets. However, the striking difference is that the upper-tropospheric warm center and precipitation in CRA-40 are greater than the others. The present study uses prevailing zonal westerly wind at 850hPa (U850), the inversion of the mean meridian temperature gradient (MTG) in the middle and upper troposphere, and the establishment of convection (OLR) in the South China Sea to define the onset date of SCSSM. Based on different indicators, the onset date of the SCSSM with the four reanalysis datasets is consistent in most years in which the circulation is completely coupled with convection. In these years, while the upper and low-level circulation is adjusting, convection over the South China Sea (SCS) establishes. However, in individual years, the onset date of the SCSSM defined by the three indicators is very different because the coupling between the upper and low-level circulation is indefinite. When the interannual variability of the onset date defined by U850, MTG, and OLR is consistent, the SST anomaly field from April to May presents a typical ENSO-type distribution, indicating that in these years, tropical sea-air interaction is the critical factor for the SCSSM onset. The SST anomaly in the Bay of Bengal in May may be the critical factor that ENSO influences the onset of the SCSSM. When the interannual variability is inconsistent, the most apparent SST anomaly appears along the California coast of the North Pacific, indicating that mid-latitude sea-air interaction may modulate the SCSSM.
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Available online:February 07, 2023 DOI: 10.3878/j.issn.1006-9895.2212.22179
Abstract:Based on the monthly reanalysis data of MERRA-2 and ERA5, EOF analysis, linear regression and composite analysis are used to analyze the interdecadal variation characteristics of aerosol pollution (Aerosol Optical Depth, AOD) in the Twain-Hu Basin in the middle reaches of the Yangtze River basin during 1980-2020 and the influence of north-south anti-phase mode of meridional wind in East Asia. The results show that the AOD in the Twain-Hu Basin region shows a non-linear trend on the interdecadal scale, with low values in the 1980s and 1990s, a continuous increase in AOD at the beginning of the 21st century, and a decline after 2010. The spatial performance is characterized by a consistent variation across the region, with the high value area mainly located in the middle of the Twain-Hu Basin, with Dongting Lake as the center in a north-south longitudinal distribution. Further analysis of the relationship between the interdecadal variation of AOD and anomalous atmospheric circulation in the Twain-Hu Basin indicates that northerly wind transport is the main meteorological cause of interdecadal variation of AOD in the Twain-Hu Basin under the influence of north-south anti-phase mode of meridional winds in East Asia. On the interdecadal scale, when the intensity and area of Siberian high pressure increase, the East Asian trough shifts westward, and the West Pacific subtropical high shifts southward, the north-south anti-phase mode of the meridional winds in East Asia tend to be in positive phase (i.e., there are anomalous southerly winds in the north of the Yangtze River and anomalous northerly winds in the south of the Yangtze River), the Twain-Hu Basin is located at the bottom of the anomalous cyclonic circulation, and the northerly winds enhance aerosol transport to the Twain-Hu Basin. Moreover, the Twain-Hu basin is in the middle of two anomalous cyclonic circulations, the pressure gradient is small and the wind speed is weak, so that the aerosol input in the Twain-Hu basin is larger than the output, enhancing the interdecadal increase of AOD in the early 21st century.
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Maliyun, chenping, Hujinggao, Yaojunqiang, Maoweiyi
Available online:February 07, 2023 DOI: 10.3878/j.issn.1006-9895.2212.22032
Abstract:Using the daily station observational data from the National Climate Center and NCEP/NCAR reanalysis data during 1951-2019, this paper analyzes the temporal and spatial distribution of the persistent extremely cold events (PECE) in northern Xinjiang and examines the interaction between stratosphere and troposphere during the occurrence and development of PECE events. The results show that on the interdecadal scale, the frequency of PECE in northern Xinjiang peaked in the 1960s, and gradually decreased since that time, means that the frequency of thePECE in northern Xinjiang is decreasing. In terms of spatial distribution, the center of the extreme value of both the frequency of PECE and the intensity of cold air locates along the Irtysh River Basin. During this period, both the stratospheric and tropospheric circulations have adjusted. First, a weak ridge was formed in Novaya Zemlya, leading to the upward propagation of the tropospheric planetary wave 1. After that, the stratospheric polar vortex over the Eurasian sector weakens from strong to weak state. Although the stratospheric polar vortex recovered and maintained its strength later, the upward propagation of tropospheric planetary wave was suppressed. Anomalously downward reflections of the tropospheric planetary wave occurred in Europe and Asia. The tropospheric polar vortex thus weakened, increased in area and move southward, causing a concurrent southward cold air. The cold air from the Arctic accumulates in front of the Ural High ridge, which is conducive to the strengthening and maintenance of the large inclined ridge. Meanwhile, the cold air at the surface forms an accumulation in the Central Siberia. Finally, accompanied by the strongly developed Siberian high pressure, the large tropospheric trough and inclined ridge lead the cold air to the south, which affected northern Xinjiang three days later.
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Available online:January 18, 2023 DOI: 10.3878/j.issn.1006-9895.2212.22183
Abstract:The underlying surface of China is complex and the driving factors of the boundary layer are numerous. At present, there is a lack of comprehensive analysis of the boundary-layer height and its influencing factors all over China. This paper uses the K-prototypes algorithm to cluster the boundary-layer height and its twelve possible influencing factors and studies the regional features of the boundary-layer height and its dominant influencing factors in summer over China, based on the high-resolution radiosonde measurements from CRN from 2012 to 2016. The results show that the boundary-layer height of the 100 stations at 08:00, 14:00, and 20:00 can be divided into four regions: northeast of China, southeast of China, northwest of China and southwest of China. On this basis, the paper then analyzes the dominant influencing factors of the boundary-layer height in different regions at different times, and studies the possible mechanism of how these factors affect the development of the boundary layer under different thermodynamic conditions. The results suggest that the development of the stable boundary layer at 08:00 and 20:00 is mainly affected by the turbulent dynamics of the wind speed, while that at 14:00 is closely related to intermittent turbulence. The development of the neutral and convective boundary layers is also mainly driven by wind speed in the morning, while at noon it is mainly driven by the turbulent thermal caused by higher surface temperature and larger net surface radiation flux. What’s more, the cloud amount and specific humidity in the northeast, the latent heat flux in the southeast, the sensible heat flux and specific humidity in the northwest, and the sensible heat flux and soil moisture in the southwest can also affect the development of the neutral and convective boundary layer through direct or indirect effects on thermal turbulence. At night, because of the time difference, wind speed tend to be the main influence factor of the neutral and convective boundary layer height in the east of Chine, while in the west of China, the main influence factors may still be the thermal factors. In addition, the leaf area index in the north of China regulates the specific humidity by vegetation transpiration, and the specific humidity can affect the boundary-layer height by regulating the surface energy distribution. Finally, it is worth noting that the surface pressure can affect the development of the nocturnal boundary layer in the northeast of China by influencing the ascending and descending movements of the air flow.
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Available online:January 12, 2023 DOI: 10.3878/j.issn.1006-9895.2209.22106
Abstract:Based on the sea surface temperture (SST) data of Hadley Center, the temperture data of 160 stations in China and the reanalysis data of NCEP/NCAR, the variability of the interannual of North Atlantic SST anomaly (SSTA) in autumn and its association with early winter temperture in China are studied by using a variety of statistical methods such as Empirical Orthogonal Function (EOF) and correlation analysis. The results suggest that the first mode of North Atlantic SST anomaly EOF in autumn is North Atlantic Horseshoe Pattern (NAH) with negative (positive) SST anomalies in southeastern Newfoundland, and positive (negative) SST anomalies in the subpolar, subtropical and eastern North Atlantic , which revealed 20.5% variance. The results show that there is a significant positive correlation between NAH SSTA in autumn and early winter temperture in most parts of China. Further analysis show that the NAH SSTA in autumn can persist until early winter. When the NAH SST is in a positive (negative) phase in autumn, the heating (cooling) of NAH SSTA over the subpolar and subtropical in early winter can cause divergence (convergence) in the upper troposphere, and stimulate the teleconnected wave train from the North Atlantic to the mid-high latitudes of East Asia, with the high-level converge (divergence) in China. As a result, through the sinking(rising) movement, the total cloud cover in the above area is reduced (increased), the shortwave radiation reaching the surface has increased (reduced), and the longwave radiation transmitted from the surface to the lower atmosphere has increased (reduced).Under the action of diabatic heating, the temperature in most areas of China is abnormally high (low). NCAR CAM5.3 was used to simulate the effects of the NAH SSTA on atmospheric circulation, radiative forcing and air temperature in early winter. The simulation results were basically consistent with the statistical analysis results of the observational data. This further confirms that the SST mode can affect the atmospheric circulation anomalies in East Asia by stimulating the teleconnected wave train, thereby affect the interannual variation of air temperature anomalies in China through the effect of diabatic heating.
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Available online:January 12, 2023 DOI: 10.3878/j.issn.1006-9895.2205.22003
Abstract:Weather radars are usually interfered by non-meteorological factors during the observation, resulting in non-meteorological echoes, which will seriously affect the accuracy of the radar"s quantitative precipitation estimation and the performance of short-term precipitation forecasts. This paper uses the scanning observations of C-band Doppler weather radars in Shaanxi (Xi’an, Yan’an, etc.), to construct a quality control method based on the Bayesian classifier and the physical characteristics of the echo: First, the reflectivity factors of precipitation echoes, ground clutter and clear-air echoes of each radar are manually extracted, and based on different types of radar echoes extracted, the reflectivity factor, the horizontal texture of the reflectivity factor, the gradient of the reflectivity factor along the radial direction, the height of the echo top and the vertical gradient of the reflectivity of the different types of radar echoes from 7 radars in Shaanxi are analyzed. And the probability density distribution functions of corresponding characteristics of different types of radar echoes are also analyzed. Then, a Bayesian classifier is established based on the statistical probability density distribution function to initially identify the radar echo. Finally, combined with the physical characteristics of the echo, the sun spike filter, the speckle filter and hole filling are designed to further identify the echo. Using the scanning observations data of 7 radars in Shaanxi Province from July to September 2019, the performance of the radar quality control method is systematically analyzed, and the accuracy of the quality control results is evaluated using the HSS score (Heidke skill score). The results of the radar data quality control method of the provincial business operations were compared and analyzed. The results show that the developed radar quality control method based on Bayesian classifiers and echo physical characteristics can better identify precipitation echoes and non-precipitation echoes, the recognition effect is better than the business results, and the HSS score is 40% higher than the business operation results.
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Available online:January 06, 2023 DOI: 10.3878/j.issn.1006-9895.2211.22105
Abstract:This study investigates the climatological characteristics of atmospheric heat source and cloud amount over Yunnan before and after summer monsoon rain onset using ERA5 reanalysis and satellite-retrieved precipitation and cloud amount data during 2001-2020. The results show that: (1) atmospheric heat source and cloud amount over Yunnan are strongly affected by the summer monsoon circulation and exhibit significant monthly changes. In June, due to the transport of water vapor by the southwesterly from the eastern Bay of Bengal, Yunnan summer monsoon rain erupts. After the summer monsoon rain onset, regional atmospheric heat source (especially latent heat) and cloud amount increase significantly relative to those in April-May, while surface sensible heat and atmospheric radiative cooling decrease. (2) Based on the method by Wang and LinHo (2002), the average onset time of the summer monsoon rain over Yunnan is approximately pentad 31 during 2001-2020. The regional atmospheric heat source (latent heat) and cloud amount correlate well with the total precipitation rate. The changes in the atmospheric heat source and cloud amount with the summer monsoon rain over Yunnan show similar annual variations as that over the adjacent South tropical monsoon region, with a single peak structure. (3) The onset time of Yunnan summer monsoon rain exhibits obvious interannual variability. The synthetic analysis shows that in early-onset years, low-level southwesterly from the southeastern Bay of Bengal can reach the Yunnan region, where the dominant divergence flow is conducive to the ascending motion and atmospheric heat source (latent heat) and cloud amount are much higher than those in late-onset years. The southern branch trough in the Bay of Bengal is weaker and the position of the Western Pacific subtropical high extends more westward in late-onset years, which is unfavorable to ascent and precipitation over Yunnan. In the peak period of Yunnan summer monsoon rain, the precipitation rate is relatively close in early- and late-onset years, but atmospheric heat source (latent heat) and high cloud amount in late-onset years are slightly higher than those in early-onset years.
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Available online:January 06, 2023 DOI: 10.3878/j.issn.1006-9895.2210.22142
Abstract:There is a significant difference in the decadal variation between June and July-August precipitation over Haihe River Basin, especially after 2002, the decadal variation characteristics of June and July-August precipitation over Haihe River Basin are opposite, so it is necessary to establish prediction models respectively. Based on the idea of year-to-year increment, several important factors related to annual increment of mid-summer rainfall over Haihe are selected through correlation analysis. Sea level pressure index (SLPI) of key areas in middle and high latitudes of Europe and Asia in the previous winter, Nino3 index in June and the difference between June and January of Nino3 index as ENSO evolution speed are used as key factors to establish the multivariate linear regression equation. Then forecast experiment of mid-summer precipitation over Haihe Basin in 2022 is conducted based on the predicted Nino3 index in June by models. The comparison between year-to-year increment model and climate model results initialed in March show that year-to-year increment has high prediction skill especially in flooding years. Then the failure hindcast case is carefully studied through the contribution of each predictor. The main factor is SLPI which reveals the relationship between East Asian winter monsoon and summer monsoon. The relationship is strongly relied on the following tropical Pacific and Indian sea surface temperature anomalies (SSTa) evolution. Nevertheless the tropical SSTA especially in western Indian during June exhibit unique feature may disturb the contribution of SLPI. It suggests that the nearly prediction of SSTa in key area highly associated with Haihe late summer rainfall should be paid attention.
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FU Yuan, YANG Jiefan, LIU Hanhua
Available online:January 06, 2023 DOI: 10.3878/j.issn.1006-9895.2211.22177
Abstract:At present, the influence of environmental field errors on the simulation effect is rarely considered in seeding models, and the conclusions are often uncertain. In view of this, in this paper, ensemble forecast model by initial field perturbation is one-way coupled with the columnar cloud model with AgI seeding scheme. The cloud model is driven in real time by using the multiple sets of thermal and micro physical profiles provided by the mesoscale model, which include the environmental field disturbance error. The multi-member, single / multi-grid AgI seeding numerical experiments were carried out to simulate the precipitation process of convective-stratiform mixed clouds in Zhejiang Province on January 23, 2022, to determine the optimal seeding scheme and the probability distribution of seeding effect. The following results are obtained. From the simulation effect of a single station (Hangzhou Station), all members of ensemble forecast can achieve positive precipitation enhancement when the amounts of AgI used at a height of 3.6 km(- 5.2 ℃) was 1.2×10-7 ~1.2×10-4g/kg at 1500 UTC on 23rd, in which the precipitation enhancement is the largest when the amounts of AgI was 1.2×10-5 g/kg, with the mean value of 4.67% and the 99% quantile of 7.77%. In the single point simulation, the initial field disturbance has a great influence on the judgment of whether excessive seeding results in precipitation reduction, for example, when the amounts of AgI is increased to 1.2 ×10-2g/kg, more than 50% of the ensemble members showed the effect of precipitation reduction, but some members still showed the effect of enhancement. Multiple grid sensitive experiments show that it should be seeding in the northwest and north of Zhejiang, especially in the northeast of Jiaxing and near Lin " an area from the perspective of the optimal probability of seeding effect. These regions also tend to correspond to relatively high average supercooled water content and low average ice crystal number concentration.
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WU Shaohua, NIU Yingli, XIE Fei
Available online:January 06, 2023 DOI: 10.3878/j.issn.1006-9895.2208.22069
Abstract:Taking the Northern Hemisphere stratospheric sudden warming(SSW) event in January 2021, which may have an important impact on the winter cold wave event in China, as an example, this study discusses the characteristics and mechanism of stratospheric sudden warming in January 2021 by using observation data, reanalysis data and prediction model. During the occurrence of this SSW event (hereinafter referred to as "event")，the Arctic stratospheric temperature rose by nearly 30 K in a few days, and the westerly winds weakened over the Arctic, and even reversed to the easterly winds three times in this event. In the early stage of the event, the Pacific Sea Surface Temperature (SST) and the Barents Kara Sea (BK) sea ice decreased abnormally; Through studying the anomalies of Eliassen-Palm (E-P flux) study, it is found that this leads to more tropospheric planetary wave propagate into the stratosphere; The increasing of planetary wave activity in the stratosphere caused by SST and sea ice may be the main factor to the SSW event. In addition, it is also found that the positive anomaly of stratospheric geopotential height propagated downward into the troposphere during the event, which is significantly related to the extreme cold event on the Eurasian continent in mid-January 2021. Finally, the stratospheric prediction model based on WACCM6 model and DART assimilation tool is used to study this event. The model successfully predicted the SSW event in January 2021. The predicted temperature and zonal wind intensity are basically consistent with the observation results. The results further show that assimilating stratospheric temperature, ozone and water vapor play an important role in accurately predicting the SSW event via reducing the errors of stratospheric circulation and temperature in the initial prediction field. If not assimilating stratospheric temperature, ozone and water vapor in the initial field, the results are very different from the observation, or even completely opposite.
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ZHAO Yufei, ZHANG Qiang, JU Xiaohui, Xiao Dong
Available online:December 26, 2022 DOI: 10.3878/j.issn.1006-9895.2212.22118
Abstract:characteristics of short-term extreme precipitation and the threshold of short-term extreme precipitation below the daily scale in the past. Based on the hourly precipitation data of 2464 stations in China from 1991 to 2021 newly developed by the China Meteorological Administration, this paper analyzes the frequency characteristics of 1-hour and 3-hour precipitation in China, uses the percentile method to count the 1-hour and 3-hour extreme precipitation thresholds respectively, and explores the climatic characteristics of short-term extreme precipitation in China. The analysis results show that the hourly precipitation frequency of some stations in Sichuan, Guizhou, Hunan, Jiangxi, Fujian and Zhejiang provinces is relatively high, up to 12%, and the hourly precipitation frequency in Northwest China is generally low, most stations are less than 3%. From 1991 to 2021, the frequency of 1-hour and 3-hour extreme precipitation showed a decreasing trend. A total of 64.7% of the stations have the linear trend of 3-hour extreme precipitation frequency in phase with that of 1-hour extreme precipitation frequency. The spatial characteristics of extreme precipitation and extreme precipitation threshold in China are obvious. The extreme precipitation threshold of one hour precipitation basically shows the spatial characteristics of large in the southeast and small in the northwest. Compared with other regions in China, the thresholds of Guangdong, Guangxi and Hainan are larger. The historical average extreme value of one hour precipitation in Hainan, Guangdong, Guangxi and Jiangsu provinces exceeded 80mm/h, of which the average extreme value in Hainan Province was the highest, reaching 102.7mm/h.
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Available online:December 26, 2022 DOI: 10.3878/j.issn.1006-9895.2212.22100
Abstract:The hot-dry stages with little rain and high temperature has an important impact on agriculture, water conservancy and human health in the middle and lower reaches of the Yangtze River (MLRYR), but there is still a lack of sufficient understanding of the historical division and long-term change law of the hot-dry stages in this region. Based on the daily temperature and precipitation data of the Meiyu season and summer at five stations along the MLRYR (Shanghai, Nanjing, Wuhu, Jiujiang and Hankou) since 1885, the quantitative standards of less rain and high temperature for the hot-dry stages after the Meiyu end date are determined respectively, and the MLRYR hot-dry stages from 1885 to 2020 are defined; combined the uniform temperature standard and the length of summer hot-dry stage, the intensity index of summer hot-dry stage for the 136 years was determined. For the 136 years, the average length of annual hot-dry stages is 21.6 days (including 16 non hot-dry-stage years and 10 autumn hot-dry years), showing 3-6-years, 36-years and 84-years cycles. Since 1951, 1959-1978 was the main peak period of the length of the hot-dry stage, 1980-1987 was the valley period, and then increased slowly; after 1980s, although the long hot-dry stage >30 days tended to decrease, the 15-30 days and high-intensity hot-dry stages occurred frequently; since 1995, the autumn hot-dry stages have increased significantly and summer has had a delay trend. The longest and strongest summer hot-dry stages in the 136 years occurred in 1934, 1967, 1978 and 2013, and the earliest/latest hot-dry stage occurred in the middle of June/middle and late September. In the past 40 years, the number of days with high temperature (≥ 35.0 ℃) in the summer hot-dry stages has increased significantly, and the incidence of high temperature in the summer hot-dry stages has increased from about 30% in the 1980s to more than 50% in recent years, posing a threat to human health. The characteristics of subtropical circulation in the long (strong) summer hot-dry stages are that the Western Pacific subtropical high stably controls the MLRYR, while in the short (weak) summer hot-dry stages, the Western Pacific subtropical high is mostly east or south, and the autumn hot-dry stages are related to the stable westward extension of the subtropical high. The evolution of high temperature days in the summer hot-dry stages is restricted by dual human activities: it is not only related to the global sea and land warming caused by human activities, but also varies from place to place, that is, it is affected by the evolution of local ecological environment and the increase or decrease of urban heat island effect. On the interdecadal time-scale, the continent-ocean temperature difference in the Indo-Pacific monsoon region is found to have an important modulation effect on the interdecadal variation of the length of the summer hot-dry stages in the MLRYR.
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WU Haopeng, NIU Shengjie, LIU Duanyang, LÜ Jingjing, ZU Fan, ZHOU Yue, WANG Yuan, GE Panyan, WANG Lingling, LU Haining
Available online:December 23, 2022 DOI: 10.3878/j.issn.1006-9895.2210.22180
Abstract:In order to further study the vertical distribution characteristics of meteorological elements and pollutant concentrations in the boundary layer of radiation fog events, a comprehensive observation test of boundary layer and pollutants was carried out in Donghai County by UAV in the winter of 2020. It is found that the thickness of inversion layer in foggy days is tens to hundreds of meters thicker than that in sunny days, and the strength is stronger by 0.5-1℃/hm. On foggy days, there is wind shear at low altitude, and the wind direction changes little in the vertical direction. On sunny day, the wind speed changes little at low altitude, and the wind direction rotates clockwise with height at low altitude. The intensity of radiation fog with deep single-layer inversion structure is stronger than that of double-layer inversion structure. In the same radiation fog process, the intensity of fog will not change with the change of wind direction, and the lower wind speed is more conducive to the formation of strong fog. From the perspective of vertical distribution of pollutants, TVOC at the same height in the inversion layer is higher in sunny days than in foggy days. Before and during the generation stage of radiation fog, the decrease rate of SO2 concentration with height is much higher than that in the same period of sunny days. In sunny and foggy days, the vertical changes of O3 and NO2 show obvious negative correlation, and NO2 shows a negative gradient change. PM1.0, PM2.5 and PM10 are more than twice higher in foggy days than in sunny days. CO is relatively stable in the process of radiation fog with little vertical change. TVOC, NO2, PM1.0, PM2.5 and PM10 will be affected by the strong inversion in the process of radiation fog and accumulate in the inversion layer. The cumulative change rate of particulate matter is more significant than that of gas, and the cumulative change rate of particles with large particle size decreases more than that of particles with small particle size. The decrease of PM2.5 concentration will reduce aerosol optical thickness and promote photochemical activity photolysis reaction, resulting in a negative correlation between PM2.5 and O3 vertical change. After sunrise, the solar radiation is enhanced, and the development of unstable boundary layer is accompanied by the downward mixing of O3 in the upper air, which leads to the increase of O3 and the increase of PM2.5 emission, making the vertical changes of the two more consistent.
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Available online:November 21, 2022 DOI: 10.3878/j.issn.1006-9895.2211.22056
Abstract:Based on 176 meteorological hourly precipitation data over mainland of the South China (Guangdong and Guangxi) and monthly reanalysis data from ERA5 (European Centre for Medium-Range Weather Forecasts (ECMWF) fifth reanalysis) from 1981-2020, and applying the objective identification technique for regional extreme events (OITREE) and synthetic analysis, this study focused on the temporal and spatial characteristics of regional extreme precipitation event (REPE) over mainland of the South China, and further analyzed circulations in the years with high and low REPE frequency. The main conclusions are as follows. In frequency, the periodic variation of REPE frequency on the interannual scale is obvious, and it has obvious monthly distribution characteristics with the peak period from May to June. In extreme intensity and impacted area, the intensity of most REPEs in Guangdong and Guangxi is about 130 mm/d, and that of few events exceeds 320 mm/d, and the impacted area of REPEs shows a significant upward trend (~310 km2/yr). In comprehensive intensity, comprehensive index Z shows a significant upward trend (0.05/10 yr), which indicates intensity of REPE has a significant increasing trend. In the Greater Bay Area and northern Guangdong, the annual accumulated precipitation of REPEs and their contribution to annual total precipitation both show a significant upward trend, while in southern Guangxi, they show a downward trend. In addition, the circulations have obvious differences between the years with high and low REPE frequency.
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Li Yafei, Ren Rongcai, Yu Yueyue
Available online:November 11, 2022 DOI: 10.3878/j.issn.1006-9895.2207.22052
Abstract:Using 1979–2020 ERA5 daily reanalysis data, this paper analyzes the statistical characteristics of blocking and its modulation on surface air temperature anomalies (SATA) during stratospheric northern annular mode events (NAMs). The results show that the four blocking highs in the northern hemisphere tend to occur in different stages of NAMs. Greenland blocking (GB) and North Pacific blocking (NPB) occur more frequently in the development stage of positive NAMs and the decay stage of negative NAMs. Ural blocking (UB) tends to occur in the decay stage of positive NAMs and the development stage of negative NAMs. The Atlantic-Europe blocking (AEB) is more likely to occur in the decay stage of both positive and negative NAMs. Although the number of days with blocking high is far less than that without blocking high during NAMs, the blocking high has a significant modulation effect on the spatial pattern of SATA related to the NAMs. When GB occurs during positive NAMs, the SATA in Eurasia changed from “overall warm” or “North warm-South cold” to “North cold-South warm” in the extratropics, while the SATA in North American changed from the “overall cold” or “North cold-South warm” to “North warm-South cold”. The UB in the decay stage of negative NAMs can not only reverse the “North cold-South warm” SATA pattern to “North warm-South cold” pattern in Eurasia, but also lead to the SATA pattern in North American changing from “North warm-South cold” to “South warm-North cold”. However, the modulation effect of AEB and NPB on the spatial patterns of SATA in most stages of NAM is not significant, that is, the spatial patterns of SATA is mainly dominated by NAMs. Under the influence of NAMs and the modulation of blocking high, Eurasia is colder and North America is warmer in mid latitudes from the peak stage of positive NAMs to the developing stage of negative NAMs, while it is the opposite from the decay stage of negative NAMs to the initial stage of positive NAMs. The dominant patterns of SATA in Eurasia and North America tend to the South-North dipole pattern between mid- and high- latitudes during NAMs. These conclusions are verified by Monte Carlo random sampling test.
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MAI Zhening, XU Dongbei, SUN Jisong, YAN Ruotong, ZHANG Yaxin
Available online:November 11, 2022 DOI: 10.3878/j.issn.1006-9895.2208.21119
Abstract:Using ERA5 500hPa hourly reanalysis data (0.25°×0.25°) and based on the synoptic characteristics of the Tibetan Plateau vortex（TPV）, an objective identification algorithm based on the grid data with high spatial and temporal resolution was designed and researched to identify the TPV over the Qinghai-Tibet Plateau during the warm season from 1990 to 2019, and to establish the TPV database. The algorithm extracted the TPV feature points by objective criteria, and adopted DBSCAN algorithm for feature point clustering analysis. Based on the coincidence, proximity and previous lifetime of the TPV between adjacent time periods, a reasonable path of the TPV was obtained to connect the isolated TPV into a dynamic vortex process. Using the Qinghai-Tibet Plateau Low Vortex Shear Line Yearbook, the comparison of the TPV in the warm season of 2017 (from May to September) and the objective identification method in this paper are compared. The results show：the monthly distribution characteristics of the objective identification TPV and the proportion of the TPV moving out of the plateau are similar to those in the Yearbook, and the typical long-life TPV can be correctly identified, which shows that the objective identification algorithm and its database have certain reliability and practicability. However, the total number of the objective identification TPV is more than that in the Yearbook of Low Vortex Shear Line over the Qinghai-Tibet Plateau, and there are also more TPV originating from "western type". The reason for this is that finer grid scale can extract the eddies from earlier lifetimes, possibly tracing the "eastern type" eddies in the Almanac further to the west. In addition, due to the serious lack of observation stations in the northwest part of the Qinghai-Tibet Plateau, the TPV generated in the northwest part of the Plateau are not reflected in the Yearbook, which is also an important reason for the difference in the number of the TPV.
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Available online:November 11, 2022 DOI: 10.3878/j.issn.1006-9895.2210.22048
Abstract:Arid and semi-arid areas are ecologically fragile regions in China. With the intensification of climate change and human activities, vegetation in this region is undergoing significant changes in recent decades. However, there is still a lack of sufficient understanding of the causes of vegetation change. Based on the GLASS(Global Land Surface Satellite) leaf area index(LAI) and CRU(Climate Research Unit) temperature and precipitation data, this paper studies the temporal and spatial variation characteristics of vegetation in arid and semi-arid areas of China from 1982 to 2017 by using correlation coefficient method and residual analysis method, and analyzes the relative contributions of temperature, precipitation and human activities to LAI changes. The results showed that: 1) Vegetation in most arid and semi-arid areas was significantly improved, and the vegetation improvement was more obvious in summer. 2) Vegetation is positively correlated with temperature and precipitation in most areas of the study area. The influence of temperature on vegetation is mainly manifested in the trend change, while the influence of precipitation is mainly manifested in the interannual change. 3) The simultaneous effects od spring and summer temperature and summer precipitation on vegetation growth in arid and semi-arid areas are significant, while in northern Xinjiang and central Inner Mongolia, vegetation has seasonal lag effect responses to climate factors. 4) Vegetation change is affected by human activities and climate change, and the dominant factors of vegetation change in different regions are various. In the vegetation-improved area, the contribution rate of climate factors is about 59%, and human activities is about 51%; and in vegetation-degraded areas, the contribution rate of climate factors is about -51% and human activities is about -49%. In general, the vegetation in arid and semi-arid areas of northern China has undergone significant changes in recent decades, which is the result of combined effects of temperature, precipitation and human activities.
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TANG Nanjun, REN Rongcai, ZHU Chuangdong, WU Guoxiong
Available online:November 11, 2022 DOI: 10.3878/j.issn.1006-9895.2207.22066
Abstract:The bimodal distribution of the South Asian high (SAH) corresponds to the east–west oscillation of its center locations on a quasi-biweekly timescale of 10–20 days in summer, which has significant impact on the water vapor distribution and transport in the upper troposphere over the Tibetan Plateau (TP) area. In this study, we used the daily averaged European Centre for Medium-Range Weather Forecasts Interim Re-Analysis (ERAI) datasets, and the phases composited analysis method which bases on the east–west oscillation indexes of the SAH in July–August. The results show that, for the TP mode of the SAH, the water vapor content is abnormal high (low) in the upper troposphere over the TP (Iranian Plateau, IP). For the IP mode of the SAH, the opposite occurs. In association with the centers of the SAH moving westward from the TP to the IP, the centers of positive anomaly of the water vapor content in the upper troposphere also gradually propagate westward from the eastern TP to the west of IP. Further diagnosis shows that, in the upper troposphere, except the abnormal meridional adiabatic transport plays a counteract effect in the northern and southern TP, the water vapor tendency anomalies over the two plateaus are mainly contributed by the abnormal zonal adiabatic water vapor transport and their convergence and divergence anomalies. While the abnormal upward diabatic water vapor transport due to convective over the TP are mainly counteracted by the residual term (water vapor condensation and evaporation). Therefore, when the water vapor content anomaly is positive in the upper troposphere over the TP (IP), there are abnormally weak (strong) convective over the TP. Corresponding to the center locations of the SAH and the centers of positive anomaly of the water vapor content in the upper troposphere moving from the TP to the IP, both the abnormal convective and upward diabatic water vapor transport continuously enhanced over the TP. Meanwhile, the water vapor condensation anomaly in the upper troposphere also continuously enhanced. Furthermore, with the SAH moving westward, the abnormal convergence (divergence) of the adiabatic water vapor transport in the upper troposphere mainly occur to its west (east) sides, which is the main reason for leading to the zonal propagation of the centers of water vapor content anomaly.
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DING Tian, GUO Zhun, ZHOU Tianjun, HU Shuai, CHEN Xiaolong, HE Linqiang, WU Mingna
Available online:November 01, 2022 DOI: 10.3878/j.issn.1006-9895.2209.22076
Abstract:Based on the reanalysis data and FGOALS-g3, this study explores the contributions of air-sea interactions to the simulation of the East Asian Summer Monsoon (EASM). For climatological mean, the Eastward shift of the Summer Monsoon Rain Belt in atmospheric general circulation models (AGCM) results in dry bias over the East Asian monsoon region. While coupled general circulation models (CGCM) present a proper position of the Summer Monsoon Rain Belt, rain in the East Asian monsoon region is weak. Due to the absence of air-sea interaction, the fake convective responses over the Northwest Pacific region lead to an eastward shift of Subtropical High, which is the main reason for the bias of AGCM in simulating the EASM precipitation. The dry humidity over land is not negligible and contributes 70% of the dry error with the help of the circulation bias. The position bias of Subtropical High and Summer Monsoon Rain Belt is significantly reduced in CGCM which reduces the dry bias by 36%. Less evaporation and less zonal water vapor transport in CGCM simulation together contribute more than 70 % dry bias. For responses to pre-winter El Ni?o, CGCM can reproduce the Western North Pacific Anomalous Anticyclone (WNPAC) and the corresponding dipole precipitation anomaly distribution in the El Ni?o decaying summer. It can also reproduce the Indo-western Pacific Ocean capacitor (IPOC) maintaining WNPAC. In AGCM simulation, convection in the Northwest Pacific, the Bay of Bengal, and the oceans surrounding the Indian Peninsula is too sensitive to SST in the El Ni?o decaying summer. On one hand, this results in strong convective mass transport in the Northwest Pacific, which inhibits the establishment of WNPAC to some extent. For another hand, strong convection in the North Indian Ocean can inhabit convection in the Indian Ocean, resulting in the inability to simulate IPOC mode. Therefore, the lack of air-sea interaction is the main reason for why AGCM cannot reproduce the two-season lag response of EASM to major El Ni?o.
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Available online:November 01, 2022 DOI: 10.3878/j.issn.1006-9895.2210.22107
Abstract:Based on Subjective and Objective Circulation Classification, a framework of method for object-based diagnostic evaluation (MODE) is developed for numerical forecast of heavy rainfall, and this framework is used to verify the heavy rainfall forecast by the global forecast model of the European Center for Medium-Range Weather Forecasts (ECMWF) and the regional mesoscale forecast model of the China Meteorological Administration (CMA_MESO) in Northeast China during the warm season of 2019. The results show that 54 heavy rainfall days in Northeast China in the warm season of 2019 can be divided into trough pattern (P1), Western Pacific Subtropical High (WPSH) pattern (P2), jet pattern (P3), western Northeast China Cold Vortex (NCCV) pattern (P4), and Eastern NCCV pattern. Among the 5 synoptic patterns above, P1 and P3 are dominated by regional heavy rainfall, and the numerical model has strong predictability for the occurrence of heavy rainfall with higher Threshold Score (TS). The heavy rainfall in P4 and P5 is locality, and the numerical model has poor predictability with lower TS. The P2 is also dominated by regional heavy rainfall. However, the forecast deviation for the location, intensity, area of the heavy rainfall is relatively larger, and the TS is also lower. In addition, from the comparison of CMA_MESO and ECMWF, CMA_MESO is generally stronger than the actually intensity and area of heavy rainfall. The TS and false alarm rate (FAR) of CMA _ MESO for heavy rainfall are both generally higher than that of ECMWF. The forecast deviation of CMA_MESO has less consistent , and the predictability of CMA_MESO is generally lower.
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XU Yuan, MIN Jinzhong, ZHAUNG Xiaoran, WANG Xiao, ZHU lijian
Available online:October 17, 2022 DOI: 10.3878/j.issn.1006-9895.2207.22103
Abstract:Warm-sector rainstorm events over the middle-lower reaches of Yangtze River (MLRYZ) usually have large prediction uncertainties due to that they are easily affected by the complex underlying surface, especially in the convection initiation stage. In this paper, high-resolution numerical simulation and convection-permitting ensemble simulations are carried out for a warm-sector rainstorm over MLRYZ on June 23, 2020 that was affected by the complex terrain to investigate the trigger mechanism and reveal the limited predictability of this event. The Lagrangian backward trajectories analysis of air parcels, sensitivity experiments of removing terrain and closing thermal effect, and ensemble sensitivity analysis are used to analyze the convection initiation stage. Results show that the lifted air parcels mainly come from planet boundary layer below 1.5 km. The valley wind driven by thermal effect of Xianxia and Shan Mountains is the dominant dynamic source that triggered local convergence and lifting. The divergence of high and low levels, the vertical configuration of moist potential vorticity and dipole potential vorticity anomaly have a good indication of the convection initiation. In addition, this event is highly sensitive to the 2 m temperature and apparent heat source at low level, indicating the importance of accurate underlying forcing to the warm-sector rainstorm prediction. The initial condition sensitivity experiments which reduce the initial errors gradually suggest that the predictability of the warm-sector convective event is significantly lower than that of the frontal event occurred in the north. The RMDTE (Root Mean Difference Total Energy) of frontal convection can be decreased continuously with the reduction of the initial errors, while the RMDTE curves of warm-sector convection still reach original level, showing a nonlinear convergence characteristic. Therefore, for the frontal convection with strong synoptic forcing, data assimilation technique may be prioritized to reduce the initial errors so as to further reduce the forecast errors. However, for the convection initiation process of warm-sector rainstorm under complex terrain, more attentions should be paid on ensemble forecasts to represent its uncertainty.
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Xu Jinghan, Ran Lingkun, Yan Lijun, Zhi Hai, Shen Xinyong, Li Xiaofan
Available online:October 12, 2022 DOI: 10.3878/j.issn.1006-9895.2205.22038
Abstract:Using the reanalysis data and WRFV3.6.1 model, the EF2-level tornado process which occurred in Sanshui District, Foshan City on the morning of 17 September 2018 was simulated at a 49m resolution in this paper. The structure of tornadic supercell and low-layer tornado-like vortex (TLV) are analyzed Using the mode data. Shearing wind helicity is introduced to diagnose the dynamic reasons for the formation of TLV. The results show that the tornado was produced by a supercell in the spiral rainband of typhoon Mangkhut. The supercell had the typical characteristics, such as hook echo, inflow notch, bounded weak echo region, and overhanging echo. The overshooting top, anvil and wall cloud can be seen on the vertical cross section of hydrometeor mixing ratio; The vertical circulation in the supercell is formed by updraft (UD) , front flank downdraft (FFD) and rear flank downdraft (RFD); TLV occurred between the low-level UD and RFD; The inside sank while the outside rose during the mature period of TLV; The diagnosis of the vertical vorticity equation indicates that the torsion term was more critical to the strengthening and upward spread of TLV during the developing period, while the stretching term dominated the changes in TLV during its mature period.
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Wen Xinsheng, Yang Shuangyan, Gao Mingxiang, Li Tim
Available online:October 09, 2022 DOI: 10.3878/j.issn.1006-9895.2207.22077
Abstract:Based on NCEP reanalysis daily data during 1979–2018, the spatio-temporal evolution of the 10–30-day atmospheric intraseasonal oscillations (ISO) at mid-high-latitude Eurasia and its effect on the European blocking frequency are investigated. The co-effect of the blocking and ISO on extreme hot event frequency is also investigated. The ISO exhibits two modes, that is, the eastward and westward propagating modes. During the eastward (westward) propagating mode, the northwest-southeast tilted quadrupole (east-west dipole) quasi-barotropic geopotential height anomaly coupled with the air temperature anomaly at the troposphere propagates southeastward (westward). Phase composite shows that, during both modes, the mid-high-latitude low-frequency Rossby wave trains significantly affect the frequency of the European blocking during the propagating journey. The most frequent European blocking appears in phases 6–7 (5–6) during the eastward (westward) mode which is referred to as E-P67 (W-P56). During E-P67 (W-P56), if there is no blocking, western Europe, the eastern European plain, the Ural Mountains, and northeast plain of China (Europe and the Ural Mountains) are respectively controlled by quasi-barotropic + – + – (+ –) height anomalies, resulting in significantly positive frequency anomalies of extreme hot events over western Europe and the Ural Mountains (Europe), and negative ones over the eastern European plain and northeast plain of China (Ural Mountains). If blocking occurs, During E-P67, the positive height anomaly intensity over western Europe increases significantly, and the positive or negative ones over the Ural Mountains, the eastern European plain and the northeast plain of China weakens. Meanwhile, a negative height anomaly appears south of Europe, leading to a negative extreme hot frequency anomaly; during W-P56, both the positive and negative height anomalies are intensified, and a positive and a negative height anomaly respectively appear over northeastern plains of China and south of Europe, respectively decreasing and increasing the hot events in the two regions. So, during E-P67 and W-P56, the European blocking increases (decreases) the frequency of extreme hot events in Europe and northeast plains of China (south of Europe and the Ural Mountains). Therefore, European blocking activities significantly regulate the effect of the two propagating ISO modes on the extreme hot events over the middle and high latitudes of Eurasia.
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Available online:September 13, 2022 DOI: 10.3878/j.issn.1006-9895.2208.22102
Abstract:Compared with heavy rainfall on daily scale such as torrential rain, short-duration heavy rainfall (≥20 mm h-1) is a more direct cause of disasters such as mountain torrents, mudslides and urban water logging.Using ground automatic meteorological stations and ERA5 reanalysis data, this study focuses on the temporal and spatial evolution characteristics of short-duration heavy rainfall over the Pearl River Delta region before and after the onset of South China Sea summer monsoon, and explores the possible causes of the characteristics and differences of short-duration heavy rainfall before and after the monsoon onset. Results show that: (1) Compared to those before the monsoon onset, the precipitation over the Pearl River Delta region after the monsoon onset has increased significantly, and the contribution of short-duration heavy rainfall has increased significantly. For the short-duration heavy rainfall itself, the regional average intensity and extremes have little difference before and after the monsoon onset, but the frequency of short-duration heavy rainfall increases by 70.0% after the monsoon onset. (2) The high incidence areas of short-duration heavy rainfall are mainly concentrated in the northeastern part of the Pearl River Delta region and the west coast of the Pearl River Estuary. After the monsoon onset, the frequency of the above-mentioned two areas increased most obviously. The frequency of short-duration heavy rainfall changed from single peak (afternoon) before the monsoon onset to double peak (morning and afternoon) after the monsoon onset. (3) Short-duration heavy rainfall has obvious regional variation characteristics. The average rainfall intensity and extremes of short-duration heavy rainfall after the monsoon onset are significantly stronger in the west coast of the Pearl River Estuary than in inland areas, the frequency peak time in coastal areas changes from the afternoon before the monsoon onset to the morning after the monsoon onset, inland areas are concentrated in the afternoon before and after the monsoon onset. (4) After the monsoon onset, the low-level water vapor during the short-duration heavy rainfall period exceeded 15.6% of the climate mean. Abundant water vapor is transported to the coast under the nocturnal acceleration of the monsoon, and combine with the land breeze to enhance the convergence, which explains the frequency peak time conversion of the short-duration heavy rainfall in the coastal area before and after the monsoon onset. (5) Compared to those before the monsoon onset, the correlation between the frequency of short-duration heavy rainfall and the low-level water vapor flux in the Pearl River Delta region increased significantly after the monsoon onset. The increase of night-morning short-duration heavy rainfall in the coastal areas of the Pearl River Delta region is related to the dynamic forcing caused by the structural change of the wind field in the middle and low layers. The short-duration heavy rainfall before and after the monsoon onset in inland areas is more closely related to the environmental thermal and unstable conditions.These results advance our understanding of the temporal and spatial distribution characteristics of short-duration heavy rainfall before and after the monsoon onset over the Pearl River Delta region and its generation mechanism.
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LI Dan, LIU Yuzhi, SHAO Tianbin, LUO Run, TAN Ziyuan
Available online:September 13, 2022 DOI: 10.3878/j.issn.1006-9895.2208.22109
Abstract:Cloud base height (CBH) plays an important role in weather forecasting and flight service. However, there is lacking in CBH data with high spatio-temporal resolution. This study evaluates the CBH product of ERA5 reanalysis data using ground-based observations in eastern China, revealing the CBH feature in China by validated CBH data from ERA reanalysis. Overall, the CBH from ERA5 reanalysis data are lower than those from ground-based measurements, in which the low-clouds and middle-clouds are overestimated and underestimated, respectively. In addition, under precipitation condition, the CBHs from ERA5 data indicate a higher accuracy for low clouds than those under non-precipitation synoptic background, while the accuracy of ERA5 CBH is lower for middle- and high-cloud. The result shows that the CBHs are lower in the daytime than those at night, peaking at 9:00 and 22:00 over eastern China in the daytime and at night, respectively. On the whole, the monthly mean CBHs from ERA5 reanalysis are consistent with the ground-based measurements in autumn and winter. The revised CBHs of ERA5 data present a gradually decrease from northwest to southeast of China during 2010-2019. Besides, the CBHs over the southern China, northeastern China and Tibetan Plateau are relatively lower than other areas. The CBHs show lower over the Tibetan Plateau in summer and autumn but higher in spring and winter. Additionally, the desert region has higher CBH in all four seasons.
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HUANG Ying, FU Danhong, GUO Xueliang, ZHANG Wenyu
Available online:September 05, 2022 DOI: 10.3878/j.issn.1006-9895.2207.22019
Abstract:Located in the northeastern Tibetan Plateau, the Qilian Mountains（QM）are the main source of several important rivers including the Shiyang, Heihe and Shule rivers. The cloud microphysical properties have a critical role in understanding the precipitation formation. However, the aircraft measurements on the cloud microphysical properties over the QM are few. By using the aircraft measurement data of KingAir-350 of the Weather Modification Office of Qinghai Province, the cloud microphysical properties of a precipitating stratiform cloud event over the QM was investigated. The results show that the formation of the precipitating stratiform event was primarily produced by the terrain lifting of nearly southerly airflow from the low topographic valley area to high mountain area. The maximum supercooled liquid water content in the orographic precipitating stratiform cloud was 1.13 g m-3. The liquid water content was relatively high in low-altitude areas due to the existence of more water vapor. The formation and growth processes of ice particles varied at different altitudes in mountainous areas. At the level of 5600 m (-5.1 ℃), the formation and growth processes of ice particles primarily depended on deposition and aggregation processes with weak riming process; at the level of 6560 m (-9.9 ℃), a large number of aggregated ice particles were observed and the spectrum broadening was obvious, indicating that the dominant formation and growth process for ice particles were deposition and aggregation processes; at 7850 m (-17.0 ℃), there were almost ice phase particles with abundant aggregated dendritic ice particles, indicating that the deposition and aggregation processes were dominant at this high altitude.
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Available online:September 05, 2022 DOI: 10.3878/j.issn.1006-9895.2209.22040
Abstract:Soil moisture is one of the key factors to control the distribution of latent and sensible heat flux at the interface of land surface and atmosphere, which can have impacts both on weather and climate processes on various temporal and spatial scales, because of its certain memory properties. In the numerical model, the uncertainty of soil hydraulic parameters is one of the main reasons for the uncertainty of soil moisture simulations. Based on the Yin He Global Spectral Model (YHGSM), this paper introduces the VG (van Genuchten) soil water retention curve model, and discusses the influence of two different sets of soil hydraulic parameters on the offline simulation of soil moisture and the global medium-range numerical weather forecast. The soil type information needed for soil hydraulic parameters comes from the Global Soil Dataset for ESMs (GSDE). The offline results show that, except for the large simulation deviation of permafrost and organic soil, the land surface module of YHGSM has a good ability to simulate soil moisture in most parts of the world, and the simulation accuracy is similar to that of ERA5 soil moisture reanalysis products. Soil hydraulic parameters have a certain influence on soil moisture, and that the influence strength is closely related to soil types and local climatic conditions, and coarse structure soil is more sensitive to model parameters. The results of the global medium-range numerical forecast experiments indicate that, by changing the soil moisture, soil hydraulic parameters not only have impacts on the short-term forecasting of near surface temperature and humidity, but also lead to significant changes in the large-scale circulation after 6-days forecast. Therefore, for the global medium-range numerical forecasting system, it is very important to optimize soil hydraulic parameters and improve the ability of soil moisture simulation.
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Trends and possible causes of different levels of precipitation variations in China during 1961~2020
Available online:August 30, 2022 DOI: 10.3878/j.issn.1006-9895.2208.22033
Abstract:Studies have shown that global precipitation patterns have changed in the context of warming, with a general decreasing trend of light precipitation and a significant increasing trend of intense precipitation in some regions. However, there is a lack of systematic studies on the variation of precipitation at different levels, especially on the regional scale. Based on precipitation data from 838 meteorological stations in China, this paper investigates the trends of precipitation at different levels in China from 1961 to 2020 and the relationship between their interdecadal component and ocean oscillation factors. The result shows that the spatial distribution of precipitation variability in China varies considerably. Light precipitation only predominantly increases in western northwest China and the Qinghai-Tibet Plateau, and significantly decreases in southern China and southwest China; moderate intensity precipitation decreases significantly in eastern part of southwest China increased in the rest of China; extreme precipitation increases in most regions, with decreasing trends only in Beijing-Tianjin-Hebei region and parts of Chongqing. In most regions of China, the contribution of light precipitation (light rainy days) to total precipitation is dominated by a decrease, while the contribution of moderate intensity rainy days and extreme precipitation (extreme rainy days) is dominated by a significant increase, the contribution of extreme precipitation in each region shows an opposite interdecadal variation to the contribution of moderate ntensity precipitation and light precipitation. The changes in the number of light rainy days and the number of moderate intensity rainy days dominate the changes in the number of total rainy days, the changes in the amount of moderate intensity precipitation and the amount of extreme precipitation dominate the changes in total precipitation. Further, it is found that on the interdecadal scale, the correlation coefficients between precipitation at different levels and Pacific Interdecadal Oscillation (PDO) in most of China tend to be negative with increasing levels, while those with Atlantic Multidecadal Oscillation (AMO) tend to be positive with increasing levels. Interdecadal abrupt changes in the correlation between precipitation at different levels and PDO/AMO in each region occurred mainly in the 1980s to 1990s.
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CHEN Yaling, WEN Jun, YANG Chuanguo, LONG Yinping, LI Guangwei, JIA Hejia, LIU Zheng
Available online:August 30, 2022 DOI: 10.3878/j.issn.1006-9895.2205.22057
Abstract:The Source Region of the Yellow River (SRYR) is the main runoff producing area and important water conservation area of the Yellow River Basin. It is of great scientific significance for understanding and exploring the land surface process and regional water cycle characteristics and revealing the impact of land-hydrological processes coupling over the SRYR. Based on the China Meteorological Forcing Dataset (CMFD), CPC Morphing Technique (CMORPH), Tropical Rainfall Measuring Mission (TRMM) and Global Land Data Assimilation System (GLDAS) precipitation from 2009 to 2018, the precipitation accuracy of four types of precipitation products is evaluated in this research. On this basis, the standalone Weather Research and Forecasting Model Hydrological modeling system (WRF-Hydro) model is chosen and driven by the optimal precipitation products to explore the applicability of this model in streamflow simulation over the SRYR. The results show that the four types of precipitation products have the ability to reflect the distribution characteristics of precipitation, while there are significant differences in quantity and detail. CMFD products perform better in capturing the evolution characteristics of the precipitation at different spatial and temporal scales. The correlation coefficient between CMFD products and gauge observation is 0.99, and the root mean square error is 0.25 mm. In terms of the ability to indicate precipitation, the overall performance of the four types of precipitation products presents that CMFD > CMORPH > TRMM > GLDAS and the average critical success index of CMFD is more than 0.93. The WRF-Hydro model calibrated by the sensitive parameters is with?good?performance in simulating monthly streamflow over the SRYR. The Nash efficiency coefficients (NSE) is above 0.92 during the calibration period, while the simulation results are significantly better in the high flow years than that in the low flow years with a NSE of 0.15 during the validation period, which is related to the non-linearity of precipitation and streamflow. This research scheme and results are potential to provide references for the large-scale watershed hydrological simulation and projection in the semi-arid region of the sub cold zone.
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Wu Yushu, 陈权亮, ZHOU Tao, HUANG Yan
Available online:August 30, 2022 DOI: 10.3878/j.issn.1006-9895.2206.22072
Abstract:This study assesses the prediction performance of the East Asian Winter Monsoon (EAWM) using seasonal hindcast data(1993-2016) from the German Climate Forecast System(GCFS2). Main features of the EAWM are well predicted by the GCFS2,including the Siberian High, the East Asian trough , the East Asian jet stream, and the surface air temperature, and precipitation over East Asia.The interannual variations of East Asian trough and East Asian surface air temperature are skillfully predicted by GCFS2. GCFS2 shows prediction skills for the EAWM index (EAWMI) defined by sea level pressure. At the same time,the EAWM-related atmospheric circulation, surface air temperature, and precipitation anomalies over oceans are also well predicted .The high prediction skills of EAWM in GCFS2 are mainly due to the successful reproductions of the EAWM-ENSO relationship and the ENSO teleconnection. The correlation coefficient between EAWM and ENSO is -0.46 (1993 – 2016), which is stronger than that of observation. This means that the enhanced EAWM-ENSO relationship in GCFS2 is helpful to predict EAWM 2 months leading or longer. The EAWMI initialized in December GCFS2 still has 0.42 prediction skills after removing the ENSO signal, which indicates another source of prediction – the sea ice coverage in the Barents-Karabakh region in winter (BK_SIC) – works. The weaken of BK_SIC leads to the enhanced Siberian high pressure (SH) and the enhanced EAWM in the observation. The change of BK_SIC in the model can increase the predictability of northeastern SH, resulting in an increase in the EAWM prediction skills for December initialized.
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Zhao Yuhui, Chen Guanghua, Wang Ziqing, Fang Di
Available online:August 30, 2022 DOI: 10.3878/j.issn.1006-9895.2208.22074
Abstract:Based on the IBTrACS dataset and ERA5 850-hPa winds from July to November in 1979-2020, the low-level large-scale circulations associated with tropical cyclogenesis over the western North Pacific are clustered into five patterns using self-organizing map (SOM). The five patterns are named Monsoon Confluence (MC), Monsoon Gyre (MG), Strong Monsoon Trough (SMT), Weak Monsoon Trough (WMT) and Easterly Wave (EW), respectively. Tropical cyclones (TCs) in the MC pattern form in the confluence zone south of the subtropical high, occupying the largest proportion. Cyclogeneses in the MG, SMT and WMT patterns are affected by the cyclonic wind shear or the confluence zone related to the monsoon trough. The EW pattern with the smallest number of cases features an easterly wave directly evolving into a TC. To select an optimal machine learning method for automatic pattern identification for a given TC circulation, comparison is carried out among three discriminant analysis models: support vector machine (SVM), k-nearest neighbors and random forest. The results show that SVM reveals the best accuracy of 0.965 and the least sensitivity to imbalanced data with recall rate and precision exceeding 0.94 for each circulation pattern. Meanwhile, the sensitivity to dataset size indicates that using SVM model, characteristic signals can be most effectively captured from relatively limited training data.
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Xinyi Wang, Shengjie Niu, Jingjing Lv, Yuan Wang, Yuchen Jin, Haopeng Wu
Available online:August 01, 2022 DOI: 10.3878/j.issn.1006-9895.2207.21244
Abstract:Updraft is one of the basic conditions for the formation of cloud and rain. In this study, the distribution of vertical velocity in clouds, the microstructure characteristics of clouds and their correlation are analyzed using airborne particle measurements of a stratified mixed cloud conducted in Hebei Province in May 2017. The results show that the vertical velocity in clouds is parabolic with height, which is smaller at the bottom of the cloud (0.75 ± 0.52 m s-1), largest in the middle of the cloud (3.64 ± 2 m s-1), and smallest at the top of the cloud (0.32 ± 0.29 m s-1).With increasing height, the shape of ice particles in the updraft zone of clouds is mainly flaky, needle-like, and column-like in order. In the updraft zone of warm clouds, the vertical velocity and liquid water content are positively correlated, with a correlation coefficient of 0.61; the cloud droplet number concentration and maximum cloud droplet diameter under strong vertical airflow conditions are larger than the corresponding values of weak updraft, and the cloud droplet number size distribution measured in strong vertical airflow is more consistent with the Г function distribution.
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Qiu yujun, Shu zhiliang, Lu chunsong, Lin tong, Dang zhangli
Available online:August 01, 2022 DOI: 10.3878/j.issn.1006-9895.2206.22042
Abstract:By using the data of microwave radiometer (MWR), placed at the foot of the Liupan Mountain at Longde station in the time period from April 2018 to November 2019, and the data of radiosonde at Pingliang station, the humidity sensitivity of retrieved temperature of MWR (TM) is studied. The humidity sensitivity rate (HSR) and the zero degree drift (ZDD) are proposed for the first time. Based on the distribution characteristics of HSR and ZDD at different altitude layers, the impact from the mountain terrain on layer humidity and temperature is studied. It shows that, ① under non-precipitation conditions, the wetter the air, the larger the difference between HSR and 1.0, and the greater the value of ZDD. ② The terrain has a great impact on the vertical distribution of layer humidity. The climbing air flow or uplift air flow increases the humidity level of layers below 3km significantly. The air humidity reaches the maximum at the layer of 500m above the top of the mountain under clear days and at the layer of 1.0-2.0km above the top of the mountain under the cloudy days respectively. The difference between TM and the station actual temperature reaches maximum by 2.7 ℃. ③ The terrain affects the vertical distribution of the layer humidity and then affects the layer temperature. The downward atmospheric radiation under the cloudy days heats the lower layer and makes the average temperature of the layers below 3 km rise by 2.3 ℃, and the temperature caused by humidity sensitivity reaches 0.9 ℃, up to 1.7 ℃.
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Available online:July 25, 2022 DOI: 10.3878/j.issn.1006-9895.2106.22073
Abstract:The development of the disturbance and stability of the time-averaged non-zonal basic flow in a baroclinic atmosphere are investigated by energy method. More attention is paid to the problems on the role of the meridional base flow to the development of the disturbance. The sufficient condition for stability and the necessary condition for instability of the time-averaged non-zonal basic flow are obtained from the generalized energy equation. With the axis of jet stream as the center, for the barotropic developing(decaying) disturbance, the perturbation streamlines must be tilting (on average) towards the upstream(downstream) direction of the basic flow on the horizontal plane.In the troposphere, for the baroclinic developing(decaying) disturbance, the perturbation streamline must be sloping upward and tilting (on average) towards the upstream(downstream) direction of the basic flow on the vertical section. The existence of the meridional basic flow will promote and strengthen the development of the disturbance, making the developing disturbance more unstable.
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Available online:July 14, 2022 DOI: 10.3878/j.issn.1006-9895.2204.21137
Abstract:China’s Northern Xinjiang is located in a typical inland arid and semi-arid area，over which anomalous precipitation plays an main role. In recent years, anomalous precipitation events have increased with rising global temperatures. In this study, the inter-decadal variability of the wintertime precipitation in Northern Xinjiang have been investigated by using the observational rainfall data of 40 stations、ECMWF ERA-Interim and NCEP/NCAR reanalysis dataset for 1979-2017. This study discusses water vapor transport characteristics of wintertime snowstorm days and possible mechanisms in four regions based on the HYSPLIT v4.9 model. Our main results are as follows: (1) The west boundary input of water vapor is mainly in each region, but a small amount of water vapor is imported from the northern boundary in the western TianShan, and some water vapor is imported from the southern boundary in the upper in the TianShan; (2) the water vapor passages are mainly located in the Eurasia of the mid-latitude westerlies in the north、the west and the western TianShan, but their exact locations are different. The water vapor transport mainly come from the Mediterranean and the Black Sea in the north, and their contribution ratios are 58.8%; The water vapor transport mainly come from the Southwest of the Caspian Sea in the west, and their contribution ratios are 70.8%; The water vapor transport mainly come from The Black Sea and the Southeast of the Caspian Sea in the western TianShan, total contribution ratios are 72.9%; The water vapor mainly come from the India and the Iran in the TianShan, and their contribution ratios are 64.2%. (3) The geopotential height anomaly shows “+ -”from south to north, and shows “- + -”from west to east in the different regions, but the intensity、the range and the location of the anomaly center are different, this difference leads to difference of influential regions.
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XIN YUTING, ZHANG WENXIA, ZOU LIWEI, ZHOU TIANJUN, ZHAO YONG
Available online:July 14, 2022 DOI: 10.3878/j.issn.1006-9895.2203.22006
Abstract:Soil erosion is an important factor affecting ecological environment and agricultural production. The three northeastern provinces of China have an area of 793,300 km2, accounting for 9.3％ of the total land area. It is one of the four black soil regions in the world and an important commodity grain base. In the context of climate change, soil erosion in northeast China and its future risks are still unclear. The main meteorological factor affecting soil erosivity is heavy precipitation. Based on this relationship, observational precipitation data of CN05.1 and APHRODITE were used to reveal the observed characteristics of rainfall erosivity in northeast China. In the mean climate, rainfall erosivity is strongest in the southeast of Northeast China. The rainfall erosivity shows an evident annual cycle. Rainfall erosivity in summer (June-July-August) contributes to more than 80% of the annual total. Based on the observational analysis, the RegCM4 dynamic downscaling model is evaluated and bias-corrected. The future changes of rainfall erosivity in northeast China under different shared socio-economic pathways (SSP1-2.6 and SSP5-8.5) are then examined. With future warming, the mean rainfall erosivity in northeast China will increase by 9.90% and 26.70%, respectively, by the end of the 21st century. Under the high emissions scenario (SSP5-8.5), higher risk of rainfall erosion is expected, with a rainfall erosivity increase of 2.7 times greater than that under SSP1-2.6 scenario, and 77.69% of area is projected to experience more severe rainfall erosivity. Therefore, it is of great significance to deploy effective emission reduction measures and take the path of sustainable development to reduce the soil erosion risk of black land in northeast China and ensure food security.
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ZHAO Yufei, LIAO Jie, ZHANG Qiang, CHEN Jie, GONG Xi, SHI Yan, SHI Mingyuan, YANG Di, FAN Shaohua, ZHOU Xuedong, CAO Lijuan, HU Kaixi
Available online:July 14, 2022 DOI: 10.3878/j.issn.1006-9895.2204.22010
Abstract:Based on surface observation data archived by the National Meteorological Information Centre, a data set of 1991-2020 China Climate Normals is developed. During the development of the data set, the metadata of the observation data since 1991 was systematically checked, verified, and revised. All elements are segmented by using the station location migration information, and the segmented processing of the temperature series is completed based on the heterogeneity test results. The segmented processing of visibility observation data is completed by using manual and automatic observation and adjustment information. The segmented processing of visibility observation data is completed. This provides a better representative climate background field consistent with the current visibility observation method. The Fourier series theory is used to deal with the harmonics of the annual daily value series of temperature and precipitation. It reflects the seasonal transformation of meteorological variables and avoids abnormal mutation characteristics. 1991-2020 China Climate Normals provides climate background information of 14 elements of temperature, precipitation, air pressure, wind direction and speed, relative humidity, water vapor pressure, cloud, weather phenomenon, visibility, evaporation, snow, ground temperature, frozen soil, and sunshine of 2438 stations in China, providing data support for weather and climate research.
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lvguanlin, Jiang Rubin, Li Zongxiang, Yuan Shanfeng, Zhang Hongbo, Li Xiao, Liu Kun, Chen Ruiling, Liu Mingyuan
Available online:June 22, 2022 DOI: 10.3878/j.issn.1006-9895.2203.22009
Abstract:By using comprehensive data obtained in rocket-triggered lightning experiment, upward negative precursors at the triggering wire tip as during the ascent of the rocket were studied. Except for those typical precursors with peak current of tens of amperes, abundant of weak current pulses were recognized, attributed to the high vertical resolution current detection. All the isolated current pulses were found to be of the weak ones, and all those typical-intensity precursors (or clustered precursors) were preceded by the weak current pulses, involving a time interval of about 20 μs. For the weak pulses, the impulsive pulses and ripple pulses, we obtained their geometric mean values of peak current (3.6 A, 32.2 A, 11.1 A), risetime from 10% peak to 90% peak (0.39 μs, 0.9 μs, 3.2 μs), duration (2.8 μs, 5.1 μs, 12.7 μs) and charge transfer (4.7 μC, 50.8 μC, 83.2 μC). The typical-intensity precursors formed visible discharge channels that can be detected by optical means, and the channel development of those clustered precursors involved stepwise features consistent with the initial sustained upward leaders, with average 2-D speed in the order of 105 m/s. The temporal and spatial relationship of adjacent precursor-producing channels was analyzed. The new precursor channel was found to initiate at the height of the previous channel tip. The significant adjustment of charge distribution due to the stepped channel extension reduced the electric field intensity in the channel region. The precursors were actually un-sustained leader development, which produced initial leader channel segment at the triggering wire tip but eventually extinguished due to the insufficient conditions.
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Available online:June 22, 2022 DOI: 10.3878/j.issn.1006-9895.2205.22005
Abstract:Fraction Vegetation Coverage (FVC) is one of the most important land surface parameters. The change of FVC directly affects the redistribution of land surface energy and then affects regional and even global climate change.SStudying the effects of increased FVC on regional climate has great significance for future projections of regional climate change, which is essential for adaptation and mitigation of global warming.SIn this paper, MODIS-NDVI index from 2001 to 2018 were used to calculate the FVC, and long-term simulation experiment of WRF model with default and actual FVC in Liaoning province respectively were simulated. The conclusions show that:S(1) The annual average temperature in Liaoning decreased by 0.48℃ due to the increase of vegetation coverage, with the largest drop of 0.71℃ in summer, 0.35 ℃ and 0.66℃ in spring and autumn, and the smallest drop of 0.2℃ in winter.SThe increase of FVC also had a significant cooling effect on the maximum and minimum air temperature, and the response of the minimum temperature to the increase of vegetation coverage was greater than that of the maximum temperature, and the increase of FVC had a good spatial consistency with the temperature cooling.S(2) The significant increase in annual and seasonal FVC from 2001 to 2018 had a cooling trend on the annual and seasonal average, maximum and minimum temperature, especially on the minimum temperature.S(3) The main reason for the decrease of air temperature caused by the increase of FVC is that the increase of evapotranspiration leads to the increase of latent heat flux and the decrease of sensible heat flux.SFor the minimum temperature, it is mainly caused by the decrease of surface temperature caused by the increase of vegetation coverage and the decrease of upward longwave radiation at night.SIn general, the more FVC increases, the more obvious the cooling effect will be, and the increase of FVC can slow down the climate warming in Liaoning Province.
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Available online:June 21, 2022 DOI: 10.3878/j.issn.1006-9895.2205.22011
Abstract:Based on the 42 years of data from 1970 to 2020, the traditional statistic methods and random forests have been used to study the influences of the typhoon in the Western Pacific on precipitation in the eastern part of northwest China (33°N-45°N，93°E-110°E，ENWC). The results are as follows. The peak values of the frequency of typhoon and precipitation are both in July, August, and September. The typhoons in the Western Pacific play an important role in the daily mean precipitation during the period of the typhoons (TP) in that month. The location and intensity of typhoons have the most significant influence on the precipitation in July and the location, intensity, and frequency of typhoons all influence the precipitation in August, while typhoons have little influence on the precipitation in September. The influences of typhoons change with location, time, and the level of precipitation. The influences of typhoons are mainly on the second mode of the EOF analysis, the heavy and extremely heavy precipitation, which shows that the typhoons are not the main factors to influence TP and the influence is indirect and nonlinear. The typhoons influence the precipitation by influencing the location and intensity of the ridges and troughs in the mid-latitude, the West Pacific subtropical high, and the vortex in the low-latitude. The model based on the random forests can fit the distribution and intensity better than the linear model, which shows that the influences of typhoons on TP are mainly nonlinear and the nonlinear influence increases with the intensity of the precipitation. The random forests model also shows that the location of the typhoon is the most significant factor to influence the precipitation in ENWC.
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JIA Shuo, YANG Jiefan, LEI Hengchi, HAN Huibang, ZHOU Wanfu
Available online:June 20, 2022 DOI: 10.3878/j.issn.1006-9895.2205.22058
Abstract:How to reconstruct time-height profile of radar reflectivity and other parameters using Volume Coverage Pattern (VCP) data to improve its vertical resolution and make it suitable for cloud microphysical research is one of popular topics in radar meteorology in recent years. Based on the volume scan data of X-band dual polarization radar with high resolution, this paper improves the column vertical profile (CVP) algorithm by varying the selection of target area, so that it can be applied to rapidly developing convective clouds and locally generated cloud with small horizontal scale. The comparison with cloud radar shows that for the local precipitation in the plateau area, the basic reflectivity (ZH) vertical profile reconstructed by modified CVP with a small area composed of 5km (radial range)×10° (azimuth coverage) can reasonably reflect the characteristics of generating cells in the high level, the gradual decreasing of ZH from high layer as well as the gradual increasing of ZH toward low layer. For the vigorous developed convective cloud in North China, the area selection strategy of original CVP was improved by adopting the varying selected radial range for high and low elevation layers. New vertical profile of ZH significantly avoids the “zig-zag” structure caused by the relatively uneven horizontal distribution of the low-level echo, while it can still maintain main characteristics of the high-level echoes of convective cloud in the vigorous developing stage as well as the transformation of cloud structure at different stages. Furthermore, comparing reconstructed results of modified CVP and original CVP, new time-height series of different polarization parameters shows cloud microphysical characteristics changing over time accurately, revealing convection generating-cells mechanisms of formation and its seeding effect on plateau; Vertical distribution characteristics of polarization variables varing with time in mature stage of convective cloud in North China could also be displayed.
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yinana, Jiang Xuegong, Dong Zhulei, Fan Ruxia, Shi Jinli
Available online:June 20, 2022 DOI: 10.3878/j.issn.1006-9895.2204.22017
Abstract:Using the WRF-chem model and sensitive tests of different vegetation coverage, a typical dust process in Inner Mongolia was simulated, and the influence of vegetation coverage on the evolution of dust weather intensity and long-distance transportation was studied. The results show that: the WRF-chem coupled with Shao_04 sand parameterization scheme can better reproduce the actual dust transportation. Sensitivity experiments of different vegetation coverage found when vegetation coverage of sand source area was increased by 5%, the total amount dust was reduced by 50%; the reduction of surface dust concentration including PM10 and PM2.5 in downstream area was more than 80% or close to 80%; the air quality was reduced from serious pollution to light pollution, which effectively improved the atmospheric environment. When vegetation coverage was increased by 15% or more, the contribution rate of large grain sand particles gradually increased, and the sedimentation rate increased during dust transportation leading to the advance of the peak concentration of dust weather in the downstream areas. The vegetation coverage increased, the leaf area index increased, and the capture effect of vegetation on fine particles was enhanced. It can be preliminarily concluded that desertification control projects such as afforestation should first be carried out in semi-desertification areas with fine particles.
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Available online:June 14, 2022 DOI: 10.3878/j.issn.1006-9895.2204.22037
Abstract:Like temporal instability, spatial instability also plays an important role for the development and evolution of disturbances in geophysical fluids. Based on the normal mode method, the spatial instability of the barotropic geostrophic flow for is investigated. The necessary condition for spatial instability of a barotropic geostrophic base flow with respect to a given small disturbances is the partial differential quotient of the potential vorticity of the base flow with respect to the latitude has the same sign as that of the phase velocity of the disturbance. Under certain conditions, like the classical temporal instability theory, the same criteria as the necessary conditions are provided, namely the Rayleigh-Kuo theorem and the Fj\o rtoft theorem.
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Chen Yuan, Zhou Yushu, Ynag Shuai
Available online:March 15, 2022 DOI: 10.3878/j.issn.1006-9895.2112.21224
Abstract:Compound extremely catastrophic weather events occur frequently in the background of global warming, and the frequent snowstorm or frozen rain event in southern China is a typical compound extreme weather event. Therefore, this study (1) analyzed the circulation characteristics and the rainfall phases of the heavy snow and freezing rain in a typical compound weather event in Southwest China, and revealed the characteristics of the two rain phases. It is found that the freezing rain occurring in the frontal strong baroclinic environment in Guizhou Province, but the snowfall occurred in the cold zone to the north of the front in Sichuan Province. Moreover, there is a significant difference in vertical circulation for that the ascent motions are over snowfall areas from low level to high level, whereas there is a temperature inversion layer in the lower atmosphere over the freezing rain area, which leads to a cold-warm-cold temperature configuration. Thus the vertical motions present a two-layer circulation mode, in which the strong ascent motions at low levels are inhibited by the descending motions at medium levels. The ascending motions are stronger over the snowfall area and the cloud top temperature is colder accompanied with the development of convection, resulting in the phase difference from the freezing rain. (2) Utilizing the generalized moist potential vorticity (GMPV) theory, which can comprehensively depict the circulation characteristics and the phase transition of water vapor, to diagnose the characteristics of the GMPV distribution during the occurrence and development of the heavy snow and the freezing rain, respectively. It is found that the anomalous distribution of baroclinic term can better reflect the atmospheric baroclinicity nearby the quasi-stationary front, as well as the location or evolution of heavy snow and freezing rain. Thus it can be regarded as one of the dynamic identification characteristics of heavy snow and freezing rain. (3) The results by calculating of the disturbed pressure equation terms show that the balance diversity between the downward perturbance pressure gradient force and the buoyancy is the main reason for the difference of the vertical circulation characteristics between snowfall and freezing rain. This study can provide references for weather analysis and operational forecast on the perspective of circulation characteristics of this type of weather，and provide reference for power operation guarantee of power generation enterprises. Key Words：Southwest China，snow and freezing rain，generalized moist potential vorticity， difference of circulation characteristics，precipitation phase
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Ziyang Lai, Yushu Zhou, Xuyang Ge, Deng Guo
Available online:February 23, 2022 DOI: 10.3878/j.issn.1006-9895.2112.21174
Abstract:A rainstorm in the west of Sichuan Basin was closely related to the occurrence and development of overshooting convection on August 19, 2019. This paper used the ERA5 reanalysis data and high-resolution numerical simulation results of WRF to reveal the formation mechanism of this overshooting convection. The results indicate that this overshooting convection process occurred under a special background that the large-scale tropopause folding in the coastal areas of China resulted in the downward of stratospheric potential vorticity (PV) over the east of Sichuan Basin. Meanwhile, there was a Tibetan plateau vortex on the Tibet Plateau and a Southwest China vortex in the basin. The overshooting convection process can be divided into three stages. (1) The convective initiation. The continental high extended westward, which led to the enhancement of pressure gradient near Sichuan Basin and then caused the low-level jet (LLJ). The cyclonic shear produced by LLJ made the airflow orthogonal to the southeast of the Tibet Plateau strengthen. In the case of the atmospheric instability, the dynamic uplift of terrain and the convergence uplift of airflow triggered the convection. (2) The development of ascending motion in the upper troposphere. The ascending motion in this case mainly related to the PV air-block developing with the diabatic heating. And the generation of PV air-block is from downward transferring of the stratospheric PV persistently resulting from the turbulent activity. The right side of the positive PV anomaly under the easterly flow is usually upward movement, which led to the development and enhancement of ascending motion from 300 hPa to the bottom of stratosphere. (3) The updraft of upper-middle-lower level near the basin was coupled and superimposed to form overshooting convection. The stratiform pattern of Mesoscale Convective System (MCS) and evaporative cooling of water vapor in dry environment caused the downdraft from 300 hPa to 600 hPa. The atmosphere maintained the ascending motion in the upper troposphere, at the same time, dry intrusion occurred in the middle troposphere, which not only intensified the unstable stratification of " upper-layer dry and lower-layer wet " over the basin, but also enhanced the convergence of air flow in the middle and low troposphere, resulting in the downdraft near 300-600 hPa in the middle troposphere turning into updraft. Due to the slantwise vorticity development in the lower layer, the ascending motion can be maintained. As a result, the ascending motion over Sichuan basin appears vertical superposition and coupling, which shows the consistent ascending motion from the lower troposphere to the lower stratosphere and means the formation of overshooting convection and the enhancement of precipitation.
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1992,16(4):482-493, DOI: 10.3878/j.issn.1006-9895.1992.04.11
Abstract:气候突变现象及其理论的研究是近代气候学一个新兴的研究领域.本文是气候突变研究评述的第一部分,着重讨论了突变,主要是气候突变的定义和气候突变信号的各种检测方法.把气候突变归纳为四类,即均值突变、变率突变、转折突变和翘翘板(seasaw)突变.并通过Mann-Kendall法的检测,发现在本世纪20年代经历了一次全球范围的气候突变.
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HUANG Ronghui, LIU Yong, WANG Lin, WANG Lei
2012,36(3):443-457, DOI: 10.3878/j.issn.1006-9895.2011.11101
Abstract:A severe drought occurred in Southwest China from the fall of 2009 to the spring of 2010. Either its persistent time and area or decreased amount of rainfall were less observed during the last 50 years. Thus, in this paper, the occurring causes of this drought are analyzed by using the NCEP/NCAR reanalysis data and SST data from the impacts of thermal anomalies in the tropical western Pacific (TWP) and the tropical Indian Ocean (TIO) on the atmospheric circulation over the TWP and South Asia. The results show that during the period from the fall of 2009 to the spring of 2010, both the TWP and the TIO were in a warming state. Under the common thermal effect of both oceans, a strong anticyclonic anomalous circulation appeared in the lower troposphere over the TWP and the South China Sea, which caused not only the strengthening of the southwest flow anomaly, but also the appearance of a low trough anomaly over South China and Central China. In this case, the northwest flow anomaly and descending flow anomaly behind the trough controlled the eastern part of the Tibetan Plateau, and water vapor was difficultly transported from the Bay of Bengal into the Yunnan-Guizhou Plateau (Yun-Gui Plateau in short). Thus, less rainfall for a long time was caused in this region. Moreover, the analysis results also show that the circulation anomaly over the mid- and high latitudes had an important impact on the severe drought. Since the polar wave guide of quasi-stationary planetary wave propagations over the high latitudes was stronger, but the low-latitude wave guide was weaker from the fall of 2009 to the spring of 2010, which led to convergence and divergence of the wave E-P fluxes for quasi-stationary planetary waves in the upper troposphere and the stratosphere over the region about 60°N and in the middle and upper troposphere over the region about 35°N, respectively. Thus, the zonal mean wind was weakened in the upper troposphere and the stratosphere over the region about 60°N, but it was strengthened in the upper troposphere over the region about 35°N. This caused an obviously negative phase of the AO (Arctic Oscillation) and brought strong winter monsoon and eastward tracks of cold waves into East Asia, which led to a weakening of cold air arriving in Southwest China. Thereby, the persistent severe drought occurred in Southwest China.
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Assessing the Quality of APHRODITE High-Resolution Daily Precipitation Dataset over Contiguous China
2012,36(2):361-373, DOI: 10.3878/j.issn.1006-9895.2011.11043
Abstract:A daily gridded precipitation dataset (APHRO) for Asia was created by the Asian Precipitation-Highly Resolved Observational Data Integration Towards the Evaluation of Water Resources (APHRODITE) project in Japan. The resolution of this dataset is 0.25°×0.25°, and the length is from 1951 to 2007. This study aims to assess the quality of the APHRO rainfall in contiguous China from the perspective of climatological mean, rainfall classes, and long-term trend. Daily rainfall records observed by 559 rain gauges are used for the comparison. The results are as follows: (1) For the mean states, the APHRO shows similar distribution of precipitation amount to station data, and can accurately characterize the seasonal migration of rain-belt. However, compared with station data, this dataset underestimates precipitation intensity, but overestimates precipitation frequency.(2) For the distribution of different classes of precipitation, annual mean precipitation amount for heavy rainfall derived from the APHRO data is lower, while the amounts for light and moderate rainfall are higher than the station data.(3) The trends of precipitation amount in China during 1956－2005 derived from two dataset are identical, the trends of precipitation frequency are also highly consistent, and both show an “increase in the west but decrease in the east” pattern. A large difference between the two datasets is found in the spatial pattern of precipitation intensity trends. The precipitation intensity derived from station data shows an increasing trend throughout the Chinese mainland in the past 50 years; the APHRO data exhibit a similar trend in the southeastern coastal region and northwestern China, but a different pattern in northern China, northeastern China, and Jianghuai region. In addition, analysis on the seasonality of interdecadal variability indicates that the characteristics of “southern China food and northern China drought” and “Jiangnan late spring drought” derived from the APHRO data are different from those derived from station data. The APHRO data tend to underestimate the trends.
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HUANG Ronghui, CHEN Jilong, LIU Yong
2011,35(4):589-606, DOI: 10.3878/j.issn.1006-9895.2011.04.01
Abstract:Interdecadal variation of the leading modes of summertime precipitation anomalies in the monsoon regions of eastern China and its association with the spatio-temporal variations of summertime water vapor transport fluxes over East Asia are analyzed by using the daily data of the ERA-40 reanalysis and precipitation data at 516 observational stations of China for 1958－2000 and the EOF analysis method. The analysis results show that there are two leading modes in the spatio-temporal variations of summertime precipitation anomalies over the monsoon region of eastern China: The first leading mode exhibits not only a characteristic of obvious interannual variation with a quasi-biennial oscillation, but also a feature of interdecadal variability, and its spatial distribution is of a meridional tripole pattern. And the second leading mode exhibits a characteristic of obvious interdecadal variability, and its spatial distribution is of a meridional dipole pattern. This shows that these two leading modes have a significant interdecadal variability. During the period of 1958－1977, the distribution of summertime precipitation anomalies in eastern China exhibited a “＋－＋” meridional tripole pattern from the south to the north, and the distribution of precipitation anomalies for 1978－1992 showed a “－＋－” meridional tripole pattern in the region, which was opposite to that for 1958－1977, but during the period of 1993－1998, since the role of the second leading mode in summertime precipitation anomalies in eastern China was intensified, the distribution of summertime precipitation in this region showed a combination of “＋－＋” meridional tripole pattern and “＋－” meridional pattern, which caused the increase of summertime precipitation in South China. Moreover, the analysis results also show that the interdecadal variation of these two leading modes is closely associated with the spatio-temporal variations of summertime water vapor transport fluxes over East Asia, which is associated not only with the interdecadal variation of the EAP pattern teleconnection-like wave-train distribution of summertime water vapor transport flux anomalies over East Asia and the western North Pacific, but also with the interdecadal variation of the EU pattern teleconnection-like wave-train distribution of summertime waver vapor transport flux anomalies in the westerly zone over middle and high latitudes of Eurasia.
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ZHANG Meigen, HU Fei, ZOU Han, et al
2008,32(4):923-934, DOI: 10.3878/j.issn.1006-9895.2008.04.18
Abstract:总结了近5年来中国科学院大气物理研究所大气边界层物理和大气化学国家重点实验室(LAPC)在第二代超声风速温度仪研制、城市边界层研究、复杂地形大气边界层探测与数值模拟、湍流机理研究、大气污染模式发展与应用等领域的主要进展，其中，第二代超声风速温度仪的野外对比测试结果表明其主要性能完全达到了国际先进水平；北京城市化发展使得北京325 m气象塔周边近地面流场已经具备了典型城市粗糙下垫面的流场特征，近地面夏季平均风速呈现非常明显的逐年递减趋势；北京沙尘暴大风时期湍流运动主要是小尺度湍涡运动，而大风的概率分布偏离高斯分布，风速较大的一侧概率分布呈指数迅速衰减，大风中风速很大的部分具有分形特征；珠穆朗玛峰北坡地区两次综合强化探测实验是迄今为止在青藏高原大型山地中实施的针对山地环流和物质／能量交换最为全面和连续的大气过程探测实验；白洋淀地区的观测研究表明，非均匀边界层具有一般边界层不具备的特点，无论是边界层结构还是湍流输送方面，水、陆边界层之间存在一定的差异，凸显其地表非均匀性的作用；为了解决不同尺度、不同类型的大气污染问题和实际应用，研制或发展完善了多套大气污染模式系统，包括全球大气化学模式、区域大气污染数值模式、城市大气污染数值模式和微小尺度(如街区尺度)范围内污染物输送扩散模式。
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Hu Fei, Hong Zhongxiang, Lei Xiaoen
2003,27(4):712-728, DOI: 10.3878/j.issn.1006-9895.2003.04.18
Abstract:大气边界层物理和大气环境是大气科学的重要领域,中国科学院大气物理研究所自成立以来在这一研究领域取导了丰硕的成果.作者重点介绍最近十多年来在大气边界层探测、大气边界层结构特征、大气湍流理论、城市和区域大气污染预测预报模式研究等方面取得的重要进展,并对大气边界层和大气环境研究的未来发展作了展望.
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YANG Xiu-Qun, ZHU Yi-Min, XIE Qian, REN Xue-Juan, XU Gui-Yu
2004,28(6):979-992, DOI: 10.3878/j.issn.1006-9895.2004.06.15
Abstract:作者以太平洋年代际振荡(PDO)现象为重点,系统地回顾了太平洋年代际变率观测、模拟和理论研究的国内外进展.在PDO时空结构方面,总结了PDO的基本观测事实,在PDO成因方面,从海洋大气相互作用观点出发比较了三类PDO形成机制的理论或假说,讨论了现有理论或假说中存在的若干问题,并提出了未来研究的方向和需要解决的关键科学问题.作者也简要介绍了东亚及中国气候年代际变化的特征及其和太平洋海表温度异常的联系,并讨论了东亚大气环流异常在PDO形成中的可能作用.
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JIANG Zhihong, CHEN Weilin, SONG Jie, et al
2009,33(1):109-120, DOI: 10.3878/j.issn.1006-9895.2009.01.10
Abstract:Climatology of the observed daily precipitation extreme indices (SDII, simple daily intensity index; CDD, the maximum number of consecutive dry days; R10, number of days with precipitation greater than 10 mm; R5d, maximum 5-day precipitation total; R95t, fraction of total precipitation due to events exceeding the 95th percentile of the climatological distribution for wet day amounts) at 550 stations in China during 1961－2000 is used to evaluate the simulation ability of 7 IPCC AR4 Coupled Climate Models, the projected change of the precipitation extreme indices over China under IPCC SRES A2、A1B and B1 is also studied. The results show that the state-of-the-art IPCC AR4 models can simulate the spatial distributions and the linear trends of precipitation extremes well. The multi-model ensemble (MME) shows the best skill, but both the MME and single model fail to simulate the interannual variability and have large biases, such as there are excessive extreme precipitation over the eastern side of the Tibetan Plateau while in the monsoon regions the modeled intensity of precipitation extremes is lower than the observation. In the 21st century the precipitation will become more “extreme”， there would be an overall increasing trend in extreme precipitation events over most of China under a warming environment, and the change scope is scaled to the emissions scenarios.
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Luo Yunfeng, Lu Daren, Zhou Xiuji, Li Weiliang
2002,26(6):721-730, DOI: 10.3878/j.issn.1006-9895.2002.06.01
Abstract:利用北京等46个甲种日射站1961～1990年逐日太阳直接辐射日总量和日照时数等资料,反演了30年来各站逐年、逐月0.75μm大气气溶胶光学厚度(Aerosol OpticalDepth,简称AOD)平均值,分析了我国大气气溶胶光学厚度的年、季空间分布特征和年代际之间的变化.结果表明:我国大气气溶胶光学厚度的多年平均分布具有典型的地理特征,除个别大城市外,100°E以东,AOD以四川盆地为大值中心向四周减少;100°E以西,南疆盆地为另一个相对大值中心.气溶胶光学厚度的各季分布具有各自的特征.20世纪60年代,我国大气气溶胶光学厚度的平均分布特征是以四川盆地和南疆盆地为两个大值中心向四周减少;70年代,绝大多数地区AOD值增加,其中从四川盆地到长江中下游地区以及华南沿海等地,AOD增加较为明显,AOD的分布和60年代较相似;到80年代,我国大范围地区AOD继续呈增加趋势,其中长江中下游地区,AOD增加相当明显,气溶胶光学厚度的分布发生了一定的变化.
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Huang Ronghui, Zhang Zhenzhou, Huang Gang, Ren Baohua
1998,22(4):460-469, DOI: 10.3878/j.issn.1006-9895.1998.04.08
Abstract:利用ECMWF所分析的1980～1989年每日各层的水汽和风场资料分析了东亚季风区夏季风的水汽输送特征，并与印度季风区夏季水汽输送进行比较。分析结果表明了东亚季风区夏季水汽输送特征明显不同于印度季风区夏季水汽输送，东亚季风区夏季水汽输送经向输送要大于纬向输送，而印度季风区夏季水汽输送则以纬向输送为主。分析结果还表明东亚季风区由于夏季水汽分布是南边大、北边小，偏南季风气流所引起的水汽平流是湿平流。因此，水汽的辐合主要由季风气流所引起的水汽平流所造成，而印度季风区季风气流所引起的水汽平流是干平流，它利于水汽输送的辐散，水汽的辐合主要是由于风场的辐合所造成。
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1999,23(6):663-672, DOI: 10.3878/j.issn.1006-9895.1999.06.03
Abstract:用中国160个站月平均降水量和赤道东太平洋Ni?o 3区海温资料研究了ENSO循环过程的不同位相与中国降水的关系。结果显示ENSO循环对中国冬、夏季降水丰或欠及时空分布有密切关系，ENSO发展年的夏季我国东部地区以雨量偏少为主，一些地区可偏少3～5成，多雨带位于江淮之间；ENSO恢复年的夏季长江及江南地区雨量偏多，其南北两边偏少；反ENSO年的夏季长江—黄河之间及东南部雨量偏少，其北边和西南正常偏多；在ENSO的准常态年夏季，长江以北为正偏差，江南除少部分地区外降水分布接近正常。还发现ENSO暖位相与中国冬季降水也有很好关系。由于本文用准常态年降水平均值代替通常的气候平均值，因而有利于更好地揭示ENSO与中国气候变化的关系。
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ZENG Qingcun, ZHOU Guangqing, PU Yifen, et al
2008,32(4):653-690, DOI: 10.3878/j.issn.1006-9895.2008.04.01
Abstract:将地球上大气、海洋、地理环境和生态各圈看成一个有机的整体进行研究，并统一协调全球气候、生态与环境变化的有关研究（如WCRP、IGBP、IHDP、DIVERSITAS及IPCC、Global Change等)，现称为地球系统动力学。它是新兴的学科，其核心之一就是要建立地球系统动力学理论模式并作模拟研究。本文主要概述了我国地球系统动力学模式研制和发展的有关现状及近年来特别是中国科学院“三期创新”资源和海洋科技创新基地重要方向项目群“地球系统动力学模式研究”启动前后所取得的阶段性成果及主要进展，指出了我国地球系统动力学模式发展应重点研究和解决的科学问题及其主要特色，其中有不少结果是新颖的和具有我国特点的。
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Wu Bingyi, Huang Ronghui, Gao Dengyi
1999,23(3):267-275, DOI: 10.3878/j.issn.1006-9895.1999.03.02
Abstract:通过大量的数据分析发现，冬季喀拉海、巴伦支海海区是影响东亚以及北半球气候变化的关键区之一，该海区海冰面积变化与大气500 hPa高度场的EU遥相关型以及东亚冬季风强、弱之间存在密切的关系。冬季该海区海冰偏多，则500 hPa高度场容易出现EU遥相关型（日本及西欧500 hPa高度场偏高），亚洲大陆上的冷高压减弱，而北太平洋海域海平面气压升高，致使东亚冬季风偏弱以及2月份入侵我国的冷空气次数减少；而冬季该海区海冰偏少时，情况正好相反。
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Wang Pengfei, Huang Ronghui, Li Jianping
2011,35(3):403-410, DOI: 10.3878/j.issn.1006-9895.2011.03.02
Abstract:The authors propose a method to separate the truncation error and the round-off error from the numerical solution. The analytical truncation error formulas of a partial differential equation are given for the upstream scheme and the centered difference scheme, respectively. The reference solution method is then introduced to separate these two types of errors for more general equations. A scheme based on the reference solution is used to obtain the approximate truncation error. Comparing the results for the upstream scheme and the centered difference scheme, the authors find that：1) the approximate truncation error is highly consistent with the analytical one. 2) The truncation errors of 1-D wave equations for the two schemes both show wavy periodicities with amplitudes being related to the parameters of computation. 3) The analytical error is suitable for the analysis of any slice of t, while the approximate one is only suitable for the analysis of a certain time range. However, the approximate error can be more easily obtained for general differential equations without a complex theoretical deduction.
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Wang Lin, Chen Wen, Fong Soikun, et al
2011,35(3):393-402, DOI: 10.3878/j.issn.1006-9895.2011.03.01
Abstract:Based on the monthly mean NCEP/NCAR reanalysis dataset and the observed surface air temperature and precipitation from 160 China stations, the seasonal march of the North Pacific Oscillation (NPO) and its association with the interannual variations of China's climate in boreal winter and spring are investigated in this paper. By employing the Empirical Orthogonal Function (EOF) analysis method, the NPO is identified as the second EOF mode of the monthly mean Sea Level Pressure (SLP) field over the North Pacific. The seasonal mean NPO indices are then defined as the average of the monthly mean indices for each season. Wavelet analysis reveals that the significant periods of the NPO indices are below 8 years for all the four seasons, indicating strong interannual variability and weak interdecadal variability of the NPO. Besides, the winter mean NPO index experiences significant linear trend towards its positive polarity. For all the seasons, NPO is featured with a large-scale meridional dipole in the SLP field over the North Pacific region and resembles the western Pacific pattern in the middle troposphere. The two surface centers are located around Aleutian Islands and the northwest of Hawaii, respectively. Their positions vary a little with season. Comparatively the south center experiences more zonal movement and the north center bears more meridional movement. Vertically the NPO is featured with an equivalent barotropic structure in summer and tilts a little westward with height for the rest three seasons. To put the NPO jet fluctuation in perspective, the positive phase of NPO is characterized by a northward shift and downstream extension of the East Asian jet stream especially in the jet exit region. The NPO variability is influential for the China's climate. Regression analysis indicate that during boreal winter the positive phase of NPO favors significant southerly anomalies along the coasts of East Asia, which may bring warm and moisture air from the south. Consequently, significant warming is observed over most areas of eastern China as well as the eastern part of the Tibetan Plateau. Meanwhile, more precipitation is observed over southeastern China, the Huaihe River valley, and several stations of northwestern China. During boreal spring, the influence of NPO is mainly confined to North China. More precipitation and weak cooling can be observed over this region in the positive phase of NPO. Such changes may be accounted for by the NPO-associated anomalous low-level wind convergence and the secondary circulation around the entrance of East Asian jet stream. In addition to the simultaneous influences, it is further found that the wintertime NPO is closely related to the temperature and precipitation of the following spring. If the NPO phase is positive in the preceding winter, significant warming will be observed over northern China and southwestern China in the following spring. Meanwhile, about 20% more-than-normal precipitation will be observed over southwestern China. Therefore, the wintertime NPO may act as a potential predictor for the climate of the following spring in China.
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Zong Haifeng, Chen Lieting, Zhang Qingyun
2010,34(1):184-192, DOI: 10.3878/j.issn.1006-9895.2010.01.17
Abstract:Based on the monthly rainfall of 160 stations over China and the sea surface temperature data in the Niño 3 region, the instability of interannual relationship between summer rainfall in China (SRC) and pre-winter sea surface temperature (WSST) in the Niño 3 region is studied by using sliding correlation, composition etc. It shows that the long-term variation of interannual relationship between SRC and WSST in the Niño3 region has obvious regionality and is more instable in northeastern and northwestern China than in eastern China. At the same time, it has a significant stage characteristic. The period from 1951－2007 can be separated into 1962－1977, 1978－1992, 1993 to present, according to the sliding correlation coefficients. Each stage has about sixteen years in length. Every turning from one stage to another is very short and is characterized by abrupt change. There are three obvious abrupt changes in the last 50 years, such as in the early 1960s, in the late 1970s, and in the late 1980s and early 1990s. Before and after the abrupt change, the correlation sign and intensity have obvious differences in some regions. It also shows that the influences of El Niño events in different stages have different features. There are two rainbelts during 1962－1977: one was located in North China, Northeast China Plain, and eastern Inner Mongolia, and the other was located in the middle reaches of the Yangtze River; there was less rainfall in the Qingling-Daba Mountains and the Yangtze River and Huaihe River valley. During 1978－1992, there was only one rainbelt located in the Qinling-Daba Mountains area and the middle and lower reaches of the Yangtze River; there was less rainfall in the Yellow River and Huaihe River valley, and North China to the south of Northeast China. And in the present stage (1993 to present), the spatial distribution of rainbelts is similar to that during 1962－1977, there are also two rainbelts located in southern China and northern China respectively. But the north rainbelt moves southward to the Sichuan Province, Chongqing, the Yellow River and Huaihe River valley, the lower reaches of the Yellow River, and Northeast China Plain; there is less rainfall in northern Hubei Province and the lower reaches of the Yangtze River; the feature of rainfall distribution is that there is more rainfall in northern China while less rainfall in southern China. So, not only the mean interannual relations between SRC and SST in the Niño 3 region but also their instabilities must be considered in the forecasting of flood season precipitation by using ENSO events.
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2001,25(3):420-432, DOI: 10.3878/j.issn.1006-9895.2001.03.11
Abstract:90年代初，国内外开展了几次大规模的热带气旋现场试验，取得了许多宝贵的加 密观测资料。利用这些资料，对热带气旋尤其是异常热带气旋开展了一系列的研究。我国科学家在国家科技攻关85-906项目中的“台风科学、业务试验和天气动力学理论的研究”等与热带气旋有关的课题和国际热带气旋研究合作项目“SPECTRUM(SpecialExperimentConcerningTyphoonRecurvatureandUnusualMovement)”中对台风的突变现象和预报技术进行了重点研究。从而在过去10年中，在台风运动突变、结构和强度突变、台风暴雨的突然增幅、热带气旋路径预报方法研究等方面都取得了新的进展。作者将对这些进展作简要综述。
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1989,13(2):193-198, DOI: 10.3878/j.issn.1006-9895.1989.02.08
Abstract:雪花是自然界的增长现象,它具有复杂的树枝状形态。我们利用细胞自动机模型在计算机上模拟出许多种类的雪花图象,反映出实际雪花生长的一些物理过程。 “奇偶规则”考虑到水汽冻结时要释放大量潜热这个物理特点,“限制规则”和“优先规则”考虑到水汽扩散到冰晶表面要选择不同的着陆位置这个物理特点。 所有模拟出的雪花和实际观测到的雪花非常相似,且具有分数维的形式。 看来,细胞自动机是模拟像雪花那样在耗散非线性动力系统中所出现的复杂形态的有力工具。
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HUANG Ronghui, GU Lei, CHEN Jilong, et al
2008,32(4):691-719, DOI: 10.3878/j.issn.1006-9895.2008.04.02
Abstract:本文回顾了关于东亚季风系统的时空变化及其对我国气候异常影响的最近研究进展。许多研究说明，东亚季风系统无论风场的垂直结构、年循环或是水汽输送和降水特征都明显不同于南亚和北澳季风系统，它是亚澳季风系统中一个相对独立的季风系统。并且，研究结果表明了东亚季风系统有明显的时空变化：其中夏季风系统在年际时间尺度上存在着一个准两年周期振荡和具有极向三极子异常的空间分布特征，并从20世纪70年代中后期起至今发生了明显变弱的年代际变化，这个变化在华北尤其显著；而东亚冬季风在年际时间尺度上存在一个准四年周期振荡，从20世纪80年代中后期起也发生了明显变弱的年代际变化，它引起了我国的持续暖冬。进一步的研究还揭示了东亚季风系统的变异是与海–陆–气耦合系统变异及其相互作用密切相关，因而，东亚季风系统可以看成是一个大气–海洋–陆地的耦合气候系统，即称之为东亚季风气候系统。此外，本文还从上述东亚季风气候系统的年际和年代际变异提出了长江流域严重洪涝灾害发生的气候学概念模型和华北持续干旱的气候背景。
