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      Volume 44,2020 Issue 5

      • 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.

      • 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.

      • WANG Yehong, ZHAO Yuchun

        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.

      • 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.

      • XU Daosheng, CHEN Dehui

        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.

      • 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.

      • 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.

      • 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.

      • 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.

      • MIN Jinzhong, WU Naigeng

        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.

      • 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.

      • 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.

      • 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.

      • 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.

      • 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.

      • 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.

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      • Ou Lijian, Yu Jinhua, Zhong Xiaoyao, Zhang Xuyu

        Available online:August 02, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21221

        Abstract:Floods and waterlogging caused by extreme precipitation bring enormous economic losses and significant human casualties for years in China. Global warming has increased the frequency and intensity of extreme precipitation events. However, the contribution of global warming to extreme precipitation events in different regions remains to be further understood. Based on the water vapor budget characteristics of summer extreme precipitation events over the Yangtze River Valley in China, the effects of SST warming trend and natural variability forcing on the intensity of typical extreme precipitation in this region were investigated. The results show that: (1) Both extreme precipitation and summer of process are accompanied by the convergence of water vapor in the whole atmosphere, and the convergence occurs in the meridional direction. The anomalous anticyclonic circulation over the northwest Pacific formed a stable moisture transport with anomalous southwest winds at the southern boundary of the region. (2) In summer when typical extreme precipitation occurs, SST is strongly positive in the equatorial Indian Ocean and tropical Atlantic Ocean, mainly contributing to the warming trend, while SST anomalies in the equatorial Middle Eastern Pacific are La Nina. (3) Numerical sensitivity tests of SST warming trend and natural variability show that the regional moisture convergence forced by SST warming trend in 1998, 2017 and 2020 is 83%, 210% and 107% of the natural variability forcing, respectively, SST warming trend is more important than the natural variability. (4) Both the SST warming trend and natural variability are caused by the anomalous anticyclonic circulation over the northwest Pacific Ocean, which causes the anomalous water vapor transport over the southwest of the southern boundary of the middle and lower reaches of the Yangtze River, leading to the occurrence of extreme precipitation.

      • 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.

      • 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 ℃.

      • Qi Duo, Cui Xiaopeng

        Available online:July 25, 2022  DOI: 10.3878/j.issn.1006-9895.2206.21149

        Abstract:An unpredicted heavy rainfall event with a maximum 8-hr accumulated rainfall exceeding 180 mm and a maximum hourly rate of 69.3 mm h-1 occurred in Mianning on June 26, 2020, inducing mountain torrents (MTs). Here, this event is studied using various observational data. The results indicated that (1) the favorable upper and lower circulation and terrain leaded to the rainstorm event. During the rainstorm, the situation at 500 hPa had little change. With the tiny westward west-Pacific subtropical high (WPSH) and the eastward mid-latitude tough, the sourthwestly wind accelerated. The forming and developing of basin vortex (BV) can be explained well by the aspect change of ageostrophic wind. The convergence between the northly wind of western BV and the sourthwestly wind in Panxi Plateau determined the occurrence and development of rainstorm. (2) The rainstorm process can be divided into two stages: The first stage, the south branch of the updraft reached to the upper troposphere by the orographic lift, cold poo lift and convergence at the mid-level troposphere. The second stage, the south branch flow was uplifted by the orographic and the cold air associated with Sichuan basin. The maximum reflectivity over 50 dBZ closed the melting level on account of the maximum vertical velocity location descended during the period of large rainfall intensity in LLS. The maximum VIL over 50 kg/m2 means the high?precipitation efficiency and rain intensity.

      • MA Yanan, CHEN Jing, XU Zhizhen, WANG Jingzhuo, and LIU Xin

        Available online:July 25, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21242

        Abstract:The convective-scale numerical weather prediction (NWP) is sensitive to the initial minor perturbation and the evolution of initial perturbation (hereafter IP) is model-dependent, flow-dependent, and scale-dependent. And it has always been difficult to construct a reasonable initial perturbation for the convection-permitting ensemble prediction systems. Based on the GRAPES 3km convective-scale model of Center for Earth System Modeling and Prediction of CMA, we use a two-dimensional random function and background error of assimilation system in GRAPES 3km to construct the large, meso, and small scale stochastic initial perturbation field. Based on the constructed different scale initial perturbations, three convective-scale ensemble forecast experiments are conducted for a typical weather process of multi-regional heavy precipitation in summer in China. The spatial-temporal evolution and spectral decomposition characteristics of perturbation energy for three IP experiments are analyzed to understand the evolution characteristics of different scale initial perturbations in a convective scale model, to provide a reference for constructing an optimal initial perturbation in GRAPES convection-permitting ensemble prediction systems. Results show that: in the GRAPES 3km convective-scale model, (1) There are significant differences in the evolution of difference total energy (DTE) in three IP experiments. The DTE of large-scale IP increases with model integration, especially in the middle and upper troposphere. However, the DTE evolution of meso and small-scale IP experiments shows an apparent diurnal cycle characteristic. Specifically, it exhibits a significant increase (decrease) from afternoon to evening (from night to morning) when the convection is active (passive), and the diurnal cycle is mainly caused by the diurnal cycle of the small-scale component of DTE. The diurnal cycle of DTE may be due to the surface heating caused by solar short wave radiation, which makes the convection more active during the day than at night, and the convection directly affects the small-scale component of the DTE. In addition, the DTE of three IP experiments increases mainly by the development of difference kinetic energy (DKE), and the difference potential energy (DPE) cannot be neglected in the lower troposphere. (2) The DTE evolution of large, meso, and small-scale IP experiments is flow-dependent. Specifically, in the mid-high latitudes, the DTE increases of large-scale IP is dominant in the region where the baroclinic instability is strong (e.g., trough region), and the DTE of large, meso, and small-scale IP experiments does not develop in the region with relatively weak baroclinic instability (e.g., the northwest flow behind trough). In the confluence region of the north and south airflow, the DTE increases of large-scale IP is still dominant. However, the DTE of all three IP experiments hardly develops in the region affected by the South China Sea summer monsoon, and there is a relatively consistent relationship between the DPE(difference potential energy) development and the ratio of large precipitation rate in this region. (4) The DTE spectrum shows that the multi-scale cascade characteristics of DTE change with integration periods. The downscaling cascade of DTE from the large-scale component to the small-scale component in the first 3 hours is powerful. However, for lead times after 6 hours, the upscale DTE growth from meso and small-scale components becomes the main characteristic of the DTE spectrum. In conclusion, it is necessary to construct a scale-dependent and flow-dependent initial perturbation structure for different unstable weather regions, especially when we build the convection-permitting ensemble prediction in regions with complex weather systems and non-uniform spatial-temporal distribution dynamic instability (such as China).

      • YANG Hao, LI Hongli, WANG Bin, ZHANG Wengang, CUI Chunguang

        Available online:July 25, 2022  DOI: 10.3878/j.issn.1006-9895.2207.22089

        Abstract:Based on precipitation and ERA5 reanalysis datasets from 1981 to 2020, this paper analyzed the variation characteristics of precipitation at different time scales over the Three-River Headwaters region (TRHR) and Yarlung Zangbo River basin (YZRB) and their responses to the Tibetan Plateau monsoon. Results show that: (1) The seasonal variation of precipitation over the TRHR and YZRB both show bimodal distribution, the peaks appear in early July and late August. The interdecadal transitions of summer precipitation occur in the early 21st century, especially the TRHR precipitation increases significantly during recent 20 years. The onset time of summer monsoon in Dynamic Plateau Monsoon Index (DPMI) and Zhou Plateau Monsoon Index (ZPMI) are ahead of precipitation increase period over the TRHR and YZRB. The interannual variation of summer precipitation over the TRHR has a good correlation with two plateau summer monsoon indexes.. Although the TRHR is close to the YZRB, the summer precipitation of TRHR is much more affected by the Tibetan plateau monsoon than that of YZRB. When the Tibetan Plateau summer monsoon strengthens (weakens), the TRHR precipitation is more (less). (2) In wet TRHR years, the South Asian High is stronger and more eastward, while the pressure at low-level over the main body of the plateau is lower than in dry years. These situations are conducive to the intersection of southwest wind and southeast wind over the TRHR, so that the warm and humid air from the South can go deep into the hinterland of plateau, resulting in stronger water vapor convergence. In wet YZRB years, there is no obvious anomaly in pressure field near YZRB or the Tibetan Plateau. The water vapor transport over YZRB mainly has two paths, one is the southwest path which from the Bay of Bengal along the south slope of the plateau, and the other one is the northwest path which from Central Asia and through the plateau. The two paths converge at the east side of the plateau and continue to transport eastward.

      • Lin Yihua

        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.

      • LI Yayun

        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.

      • Zhangjingyi, Wanggaili

        Available online:July 14, 2022  DOI: 10.3878/j.issn.1006-9895.2204.21185

        Abstract:Mêdog, located in the southeast of the Tibetan plateau (TP) and in the valley of the lower reaches of the Yarlung Zangbo River, is the main water vapor channel from the Indian Ocean into the TP. Mêdog is also an important part of the TP precipitation system due to its largest annual average precipitation amount over the TP. Based on the Ka-band cloud radar (KaCR) observation data at the Mêdog National Climate Observatory in 2020, this paper firstly preprocessed the power spectrum data of the KaCR, which were verified by comparing with the observations from precipitation phenomenometer. Then, two weak stratiform precipitation processes occurred on March 6 and August 24, 2020 were selected, and raindrop spectrum were retrieved from power spectrum data of the KaCR to explore the microphysical characteristics of weak precipitation in the dry and rainy seasons in Mêdog. The results showed that a systematic error of reflectivity factor reached about 12 dB between KaCR measurements and the theoretical values of KaCR calculated from precipitation phenomenometer. A very good agreement between the two datasets is evident after KaCR was corrected. Furthermore, the near-surface raindrop size distribution (RSD) retrieved from KaCR was close to those observed from precipitation phenomenometer. The heights of bright band in Mêdog varied with seasons, and were low in dry season (i.e. about 1.5 km)and high in rainy season(i.e. about 4 km), respectively. The spectral width of RSD for the weak stratiform precipitation cases was narrow, and the diameter of raindrop did not exceed 3 mm in Mêdog. Above the bright band,the diameter of small ice particles increased slowly with the decreasing height according to the spectrum skewness and kurtosis. However, the growth of ice particles in dry season is more obvious than that in rainy season. Below the bright band, the ice particles converted into liquid water drops, whose concentration decreased as the height decreased in the process of falling probably due to coalescence and evaporation of raindrops. The smaller the diameter, the faster the concentration of raindrops decreased. Near the ground, a significant decrease in the concentration of raindrops may be contributed to enhanced evaporation.

      • WU Yuting, YANG Song, 鲁萌萌

        Available online:July 14, 2022  DOI: 10.3878/j.issn.1006-9895.2205.21197

        Abstract:The summer surface air temperatures over Eurasia exhibit significant warming trends in recent decades. Based on the ERA5 reanalysis data, this study investigates the characteristics of the changes in summer surface temperatures over different Eurasian regions during 1979-2019, reveals the similarities and differences among the various regions, and explains the contribution factors by adopting a climate feedback response analysis method. As the highest terrain in the world, the Tibetan Plateau (TP) has experienced a remarkable warming trend in the past several decades. The lower-elevation regions surrounding the TP such as North Africa, southern Europe, Mongolia, and Northeast Asia also show obvious warming features, while surface temperature does not change significantly in South Asia to the south of the TP. The decreased summer surface albedo due to melting snow allows more incoming shortwave radiation to reach the surface, amplifying the surface warming over the TP. The warming over North Africa and southern Europe is mainly attributed to the increase in shortwave radiation due to reduced aerosols. Meanwhile, the increase in downward longwave radiation caused by increased atmospheric temperature presents a significant contribution to the warming over North Africa, southern Europe, and Mongolia. Moreover, the reduction in clouds is the main factor contributing to the surface warming over Northeast Asia. In South Asia, the warming induced by increased atmospheric water vapor and decreased surface sensible flux is offset by the cooling due to increases in clouds and aerosols, leading to small long-term change in the regional summer surface temperature.

      • YU YUEYUE

        Available online:July 14, 2022  DOI: 10.3878/j.issn.1006-9895.2206.21250

        Abstract:Stratospheric sudden warming (SSW) events are one of the important predictability sources of extended-range prediction of cold air outbreaks (CAO) because of their temporal lead information relative to tropospheric circulation changes. Nevertheless, there is large uncertainty in the region and time of surface air temperature response to SSW events, and the stratosphere-troposphere coupling process and mechanism involved are not very clear yet. Using ERA5 reanalysis data from 1979 to 2021, this study focuses on the "displacement"-type strong SSW event in the 2020/21 winter and investigates the characteristics of extratropical surface air temperature anomalies, the evolution of coupling mode of the poleward warm air stratospheric branch (WB_ST), poleward warm air tropospheric branch (WB_TR) and equatorward cold branch (CB) of isentropic meridional mass circulation (IMC), and the related wave dynamics. Results show that associated with this strong SSW event, the CAO events over Eurasia occurred before the subpolar westerly became easterly, while and the CAO event over North America took place after the subpolar westerly recovered. This was mainly the result of three-stage coupling modes between the three IMC branches during the stratospheric polar vortex oscillation, i.e., in-phase strengthening of WB_ST and WB_TR/CB, out-of-phase with a strengthened WB_ST but a weakened WB_TR/CB, and out-of-phase with a weakened WB_ST but a strengthened WB_TR/CB. The stronger CB resulted in the CAOs associated with SSW, while the stronger WB_ST dominantly contributed to the occurrence of SSW and the continuous strengthening of the negative phase of Arctic Oscillation. The coupling mode of the three IMC branches depended on the westward tilt of waves at the two critical level, namely the tropopause level and the middle and lower tropospheric level. Anomalously strong westward tilt caused net poleward mass transport above this level and net equatorward transport below it and vice versa. Especially in the period of polar vortex recovery, the anomalously weak baroclinicity near the tropopause strengthens the WB_TR, and then strengthens the CB due to the mass continuity, which is conducive to the occurrence of CAOs. The coupling evolution mode of IMC around SSW in 2020/2 winter is found to be highly consistent with that during the negative Northern Annular Mode (NAM) events over the past years, which are characterized by lagged downward propagation of the polar stratospheric temperature anomaly to the lower troposphere. Their common features in terms of wave scale are found, that is, the wavenumber-1 waves tend to be stronger and propagate upward in the early stage of SSW event or negative NAM event, and the wavenumber-2 waves are strengthened but restrained within the troposphere after SSW.

      • 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.

      • 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.

      • Zhao Wei, Hao cui, Cao Jie, Zhou xuan

        Available online:July 14, 2022  DOI: 10.3878/j.issn.1006-9895.2204.22028

        Abstract:Using the long-term hourly precipitation data of twenty national stations in Beijing in recent forty years, this study investigates the temporal and spatial distribution characteristics of diurnal variation of summer precipitation in Beijing. Results are as follows:(1) The precipitation amount is small in the Northwest Mountainous Area and large in the plain, and the slope in the transition area from mountainous to plain is the largest; On the contrary, the precipitation frequency in plain is less than that in mountainous area; The precipitation intensity is weak in the northwest and strong in the East. The intensity and extremes of summer precipitation in Beijing are strong, and the risk of disaster is high.(2) The diurnal variation of precipitation amount in summer in Beijing is single peak type, the precipitation frequency is double peak type, and the precipitation intensity is multi peak type. They reach the maximum at 22:00 (Beijing time) and the minimum at 12:00.(3) The peak time of precipitation varies with the month, the earliest in June, the second in July and the latest in August; The peak precipitation amount is the largest in July, followed by August and the smallest in June.(4) The spatial distribution of the peak precipitation amount, peak precipitation frequency and peak precipitation intensity have strong consistency. They appear before 20 o’clock (BTJ) in the Northwest Mountainous area, and on or after 20 o"clock in the other 16 stations. The diurnal variations of precipitation amount, precipitation frequency and precipitation intensity in the two regions have completely different distribution characteristics. (5) In the past 40 years, the precipitation structure in Beijing has been continuously adjusted, and the short duration precipitation dominant period and long duration precipitation dominant period appear alternately. Before 2000, it was dominated by short duration precipitation within 6 hours, and the long duration precipitation greater than 6 hours increased significantly in recent 15 years.

      • TAN Yan, HUANG Wei, YANG Yuhua, CHEN Baode

        Available online:June 24, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21097

        Abstract:Considering the various sources of uncertainty in regional model forecasts, the initial condition uncertainty (IC), lateral boundary condition uncertainty (BC), model uncertainty (PHY) are introduced to construct a new generation of East China regional mesoscale ensemble forecast system (SWARMS-ENV2). Experiments were carried out during 2020 Meiyu season. By selecting typical cases to adjust the parameters of the stochastically perturbed parameterization tendency(SPPT), it is found that the selection of parameters have certain universality, and the influence of the random process is strengthened, the wind field and humidity field of low level in the system have obvious feedback, the ensemble spread could be improved. The influence of the three parameters on the forecast were as follows: the variance in gridpoint space, the spatial length scale (or spatial decorrelation) and temporal decorrelation time. Comparing the new version of SWARMS-ENV2 with the SWARMS-ENV1, it can be seen that the RMSE of SMS-EnWARMSV2 is reduced and the ensemble spread is obviously increased, the precipitation forecast capability is improved in all forecast period for different magnitude of precipitation, whether it is TS score or the results of probability forecast scores, and the uncertainty of physical process has an obvious influence on heavy precipitation events, and the forecast reliability of the system is improved.

      • 刘黎平

        Available online:June 24, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21199

        Abstract:Reflectivity calibration error, attenuation in rain area and water cover over cloud radar antenna had serious effects on retrieved microphysical and dynamic parameters with reflectivity spectral density data, it is key problem to analyze these errors in retrieving microphysical and dynamic parameters. Aiming at reduce the effects of observation bias of reflectivity introduced by calibration and attenuation of water cover over cloud radar antenna, a retrieval algorithm for air vertical motion (Vair) and raindrop size distribution (DSD) based on reflectivity spectral density data and dual wavelength ratio (DWR) constraint with Ka/Ku dual-wavelength cloud radar (DWCR) are presented in this paper, The disdrometer data were used to examine the retrieved parameters. The effects of air vertical speed on retrieved microphysical parameters are discussed. In the algorithm (DWR-SZ), Vair retrieved from single Ka/Ku band CR (ST) and DWCR algorithms (DWSZ) are merged to form Vair in all of observation area, then the initial DSD and attenuation are retrieved by using DWSZ algorithm. Finally, DWR between first and last ranges in liquid area in a beam are used to adjust the reflectivity bias and retrieved final DSD to minimize the difference between the cloud radar observed and calculated DWR. Two convective precipitation cases in June 8, 2020 and June 1 2021 in Longmen, Guangdong Province, are used to examine the retrieved results. The results show that the radar sensitivity variations have little effects on Vair retrieved from DWSZ, however, the DWSZ cloud only used in the areas containing big rain drop (diameter large larger than 1.8mm). ST algorithms wit Ka and Ku data underestimated Vair, however, the Vair are reasonable in low levels with reflectivity weaker than 35dBZ. Highly sensitive work mode with pulse compressions could improve the Vair retrieval bias. Merged Vair from ST and DWSZ algorithms are reasonable. The attenuation and far radar range could introduce the underestimations of Vair with ST algorithms, the underestimations of Vair in solid precipitation area are negational due the sharp variation and narrow of reflectivity spectral density data. Using constraint condition of DWR reduced the bias of observed reflectivity and effects of water cover over antenna, improve the retrieval results. Vair from ST used in DWR-SZ overestimated drop number, liquid water content (LWC) and attenuation coefficient and underestimated drop size, however, it has no effects on reflectivity bias produced by water cover over antenna.

      • 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.

      • Yi Xue, Li Deqin, Yangsen

        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.

      • WeiWen, ZhuangBingliang, LinHuijuan, ShuYu, WangTijian, ChenHuimin, GaoYiman

        Available online:June 21, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21125

        Abstract:Studies have shown that there is a certain connection between the serious near-surface air pollution in East Asia and the Upper jet stream. Based on the NCEP/NCAR daily wind field, vertical velocity data, and ground pollutant and meteorological element data from Science Data Bank, this paper uses statistical analysis to preliminary explore the relationship and mechanism between the East Asian jet streams and the high-concentration air pollutants near the ground in the winter. The results show that the concentrations of particulate matter in the North China Plain is much higher in the winter of 2013-2018. The average concentrations of PM2.5 and PM10 in the North China Plain were 80.65μg/m3 and 118.62μg/m3 and the number of days exceeding the environmental standards reached 459 and 489 days in all, respectively. During this period, the concentration of particulate matter showed a slow downward trend year by year, and the average PM2.5/PM10 was about 0.65, and this ratio remained stable for many years. the concentration of air pollutants in the North China Plain has a significant relationship with the intensity of the East Asian polar front jet, and they may be related by ground temperature and meridional wind. When the strength of the polar front jet is weakened, the surface temperature decrease and the ground meridional wind weaken in the North China Plain, so that the PM10 concentration in the central part of the North China Plain and the PM2.5 concentration in the northern part of the North China Plain are both lower; when the strength of the polar front jet increases, the surface temperature rise and meridional wind strengthen, which possibly lead to higher concentration of PM10 in the middle part of the North China Plain and PM2.5 in the north part of the North China Plain .

      • Wang Xu, Zhang Lifeng

        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.

      • yuanling, Ma Yaoming, Chen Xuelong, Wang Yuyang

        Available online:June 21, 2022  DOI: 10.3878/j.issn.1006-9895.2204.21208

        Abstract:The uncertainties of evapotranspiration (ET) products developed based on satellite remote sensing and observations with different spatial and temporal resolutions still exist in the Tibetan Plateau (TP), limiting the application in hydrometeorological and climate assessment. Six ET (PML, EB-ET_V2, GLEAM, GLDAS, ERA5 and MOD16) products were evaluated based on eddy observations and the differences between the products were compared, and the uncertainty of ET products in the TP region was analyzed. The results show that: (1) There is a good correlation and consistency between the flux towers and the ET products of the corresponding pixel, and the seasonal changes can be captured. GLEAM has a high degree of agreement with the measurements and has applicability. MOD16 has poor performance at most sites. (2) Spatially, GLEAM has higher correlation (the correlation coefficient, R>0.88) and consistency (Index of agreement, IOA>0.89) with EB-ET_V2 and GLDAS. There are big differences in the temporal and spatial distribution of various products in the seasons, especially in spring. Compared with other products, MOD16 is underestimated in summer and overestimated in winter in most regions. (3) The annual average ET of each product except MOD16 is quite different. The ranking of the average ET for many years is ERA5 (401.46mm/year)>PML (334.37mm/year)>GLEAM (298.46mm/year)>EB-ET_V2 (271.39mm/year)>GLDAS (249.67mm/year). The total annual evaporation in the effective area is 330.59mm/year. The assessment results table helps to have a deeper understanding of the quality and dynamics of ET products on the TP, which can provide a reference for water resources assessment and regional water management on the TP.

      • zhangming, wangwei, zhongquanjia, dingruiqiang, lijianping

        Available online:June 21, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21236

        Abstract:There are many complex multi-scale systems in real life. Studying these coupled systems can help us to gain a more comprehensive understanding of the dynamical properties of the systems. In this paper, the implications of coupling strength on chaotic attractors and their predictability are investigated by varying the coupling coefficients of a coupled Lorenz model, which combined with a fast and slow dynamics. The results show that as the coupling coefficient increases, similar low-frequency variations to those of the slow dynamics can be found in the fast dynamics, along with its attractor becoming larger; while the high-frequency variability of the slow dynamics increases. The predictability limits of the system are investigated using the nonlinear local Lyapunov exponent (NLLE) method. It is found that after coupling, the natural logarithm curves of error growth of both the fast and slow dynamics consist of two distinct growth rates, with the first period being the fast error growth and the second period being the slow error growth process. Furthermore, the saturation value of the error growth varies from the strength of the coupling. However, the sensitivity to the coupling coefficient is not the same for the predictability of systems of different scales. Increasing the coupling coefficient leads to a larger attractor for the fast dynamics, providing more predictable information, which offsets the effect of a reduction in the predictability limit due to the increased error growth rate, ultimately leading to a longer predictability time for the fast system. However, for the slow dynamic system, the size of the chaotic attractor is minimally affected by the strength of the coupling, but an increase in the coupling coefficient will significantly add the instability of the slow dynamics, thus reducing the predictability limit of the slow system. Finally, this study can provide new insights into the predictability of such complex climate systems.

      • HUANG Chuhui, LI Guoping, NIU Jinlong, CHEN Bei

        Available online:June 20, 2022  DOI: 10.3878/j.issn.1006-9895.2205.21205

        Abstract:The dynamic and thermal structure evolution, trigger mechanism and topographic influence of the heavy rainstorm process happened in Lushan, Ya "an, Sichuan province on August 10, 2020 are analyzed using the ERA5 reanalysis data, combined with the ground encrypted observation data and the three-source fusion precipitation data provided by the Meteorological Information Center of China Meteorological Administration. This study reveals the configuration of water vapor, dynamic and thermal structure evolution and triggering mechanism of heavy rain in warm region under the background of weak synoptic-scale forcing and special topography.The results are as follows. (1)This rainstorm belongs to the warm rainstorm of southeast wind type under the background of no obvious influence system at 500hPa and no jet stream at lower level.This precipitation was short and intense,which was induced by the joint action of the West Pacific Subtropical high moving westward, the strengthening of warm and wet airflow from southeast and the weak vortex convergence airflow at 850hPa under the influence of Ya an"s "windward slope" and "Horn mouth" topography and Lushan"s southwest "?" type canyon topography. (2)From the beginning to the strong period of precipitation, the uplift velocity, cyclonic vorticity and horizontal convergence caused by boundary layer topography were always superimposed with systematic vertical upward movement, vorticity and divergence, which enhanced low-level convergence, intensified vertical upward movement and promoted precipitation intensification.(3)Differential advection of θse enhanced convective instability in rainstorm area.The weak cold advection of θse in 500hPa was also one of the triggering factors of rainstorm in warm region when in a high energy and high humidity environment with zero convective suppression energy.The cold mountain wind advection in the evening triggered the initial convection and distributed along the 1500 m terrain line. A γ meso-scale convergence line was formed on the west side of the "?" type valley and maintained by upstream heavy precipitation which caused thunderstorm cold pool outflow and mountain wind. After rapidly descending the mountain, the cold pool also remained near the mountains on the east side of the "?" type canyon, forming a strong temperature gradient. These factors triggered and maintained the torrential rain in Lushan at night.

      • LI Dan, XU Xiaoqi, JIA Xingcan, LU Chunsong, QIU Yujun, SHAO Naifu, ZOU Qingyao

        Available online:June 20, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21190

        Abstract:The dispersion of cloud droplet spectral dispersion is an important parameter that cannot be ignored in the parameterization of autoconversion, and has an important influence on surface precipitation. In this study, the weather research and forecast coupled with chemistry (WRF-Chem) model was used to simulate a precipitation process in the middle and lower reaches of the Yangtze River from January 3, 2019, to January 6, 2019. Different values of cloud droplet spectral dispersion (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) were set to study the microphysical changes of cloud and precipitation under the clean and polluted backgrounds. The results show that the precipitation in this case mainly comes from the autoconversion from cloud droplets to rain and the accretion of cloud droplets by rain. The accumulated precipitation under the clean condition is greater than that under the polluted condition because the concentration of cloud droplets is smaller under the clean condition, which is beneficial to autoconversion and accretion. Although the autoconversion and accretion are dominant during precipitation processes, the main reasons leading to the increase of accumulated precipitation with the increase of cloud droplet spectral dispersion are as follows: With the increase of cloud droplet spectral dispersion, the mass concentration of ice particles increases, which leads to the enhancement of melting process and more raindrops, thus enhancing surface precipitation. The results will improve the theoretical understanding of the response of cloud and precipitation process to aerosol and cloud droplet spectral dispersion.

      • 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.

      • 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.

      • Peng Jingbei

        Available online:June 20, 2022  DOI: 10.3878/j.issn.1006-9895.2101.21166

        Abstract:Two successive severe cold waves invaded eastern China during the period from the late 2020 to early 2021, leading to extensive, severe and persistent drop in temperature. The paper investigates the features and formation mechanisms of the circulations associated with these two cold waves. The main results are as follows: 1) The circulations of these two cold waves are both be recognized as a kind of “anticlockwise turning of transverse trough”. However, a broad ridge (or blocking high) was maintained over the Ural area from mid-December 2020 till the end of the second cold wave. No breakdown or “discontinuous westward shift” of blocking high was observed, which is different from the common cold waves in eastern Asia. 2) The maintenance and strengthening of northerly wind in front of the Ural high leads to the increase of baroclinicity in situ. In the downstream, the gradient of the geopotential height contour in the south of the transverse trough rapidly increases and the cold temperature advections are consistently enhanced and southward advanced. All of these cause the intensification and southward expansion of the Siberian High. 3) Prior to the occurrence of the two cold waves, the energy of low frequency stationary wave originating from at 0°E (or even to the west) propagates eastward, which favors the maintenance and intensification of the Ural ridge and the development of the trough downstream, providing a favorable condition for the southward outbreak of cold air.

      • HUANG Lijun, CUI Xiaopeng

        Available online:June 15, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21227

        Abstract:The Northeast China Cold Vortex (NCCV) is a significant circulation system affecting the weather and climate in the northeastern China (NEC). On the basis of previous studies, the identification and tracking method of NCCVs is constructed in this study. 2000-2019 NCEP/NCAR reanalysis data are used to objectively identify and track NCCVs. On this basis, the temporal and spatial distribution characteristics, duration, intensity and size of NCCVs are analyzed, and the relationship between NCCVs and precipitation in the warm season in the NEC are also discussed by using the hourly precipitation observation data offered by 216 national automatic weather stations (AWSs). NCCVs in the NEC have no obvious long-time trend, but have a considerable interannual variability and a clear seasonal variation, which are more likely to occur in the warm season. The duration of NCCVs is generally 48-72 hours and the size range mainly distributes in 600-1200 km. The mean size and intensity of NCCVs in the cold season are both larger than those in the warm season. The high occurrence of NCCVs presents an east-west zonal distribution along the latitude of 45-55°N. The contribution of NCCVs to the precipitation in the warm season in NEC is generally over 20%. For the precipitation in four classes of 0.1-5 mm/h, 5-10 mm/h, 10-20 mm/h and ≥20 mm/h, the spatial distributions of precipitation proportion are different and the local characteristic of heavy precipitation is remarkable. The maximum contribution of NCCVs to the rainstorm can reach more than 70%.

      • Zheng Lin-Lin

        Available online:June 15, 2022  DOI: 10.3878/j.issn.1006-9895.2205.21023

        Abstract:A Severe Convective case occurred at the rear of northeast Cold Vortex (SCCV) on May 14, 2017, in the Yangtze Huaihe region, which caused short-term intense precipitation, hail and high wind. The ensemble Kalman filter technology is used to assimilate the radar radial wind, radar retrieved wind, GPS water vapor data, radiosonde and hourly surface observation data. Observation and simulation results demonstrated the impact of Dabie Mountains on the development of the SCCV. When the SCCV moved closer to the Dabie Mountains, local convections initiated in the northern Dabie Mountains and strengthened twice subsequently. When the SCCV moving southward, its cold pool flowed to the topography and then uplifted. The solar radiation heating led to the unstable stratification on the Dabie Mountains. The two processes triggered the local convection in the Dabie Mountains. Several local convective cells initiated successively in the Dabie Mountains. The cold pool of the SCCV superposed to that of dissipating cell, leading to cold pool reinforcement, which then promote the development of new cell, and this is the first strengthening process. The second strengthening process is the result of boundary layer uplift, thermal effect of the Dabie Mountains and cold pool. When synoptic scale system moving southward, the boundary layer frontal zone (850hPa and 925hPa) moved southward and overlapped with the outflow of surface cold pool, which enhanced the boundary layer uplift. Simultaneously, the thermal heating in the Dabie Mountains in the afternoon formed thermal uplifting on the one hand, and formed the upslope wind on the southern slopes of the Dabie Mountains on the other hand.

      • Wang Teng, Sun Bo, Wang Huijun, Duodian Luozhu, Zhuo Yong

        Available online:June 15, 2022  DOI: 10.3878/j.issn.1006-9895.2204.22034

        Abstract:This study investigates the interdecadal variations of winter precipitation and associated physical mechanisms over the Three River Source (TRS) region based on gridded CN05.1 and NCEP/NCAR reanalysis datasets for the period of 1961/1962–2006/2007. Results indicate that the winter precipitation over the TRS region experienced an intensification in the late 1980s. The decadal changes are modulated by the anomalous low over the Ural Mountains and the anomalous high extending from Lake Baikal to Northeast China, which may be associated with the ocean–atmosphere interaction over the North Atlantic. Specifically, after the late 1980s, the warm SST anomalies over the mid-high latitudes of North Atlantic can contribute to the abnormal ascending motions, strengthening the convection over that region and triggering the eastward wave train, causing the anomalous low over the Ural Mountains and the anomalous high extending from Lake Baikal to Northeast China. On the one hand, the coincidence of anomalous low and high induced the enhancement and southward shift of the polar front jet, causing the upper-level divergence and development of convection over the TRS region. On the other hand, the anomalous easterly wind over the TRS caused by the anomalous high extending from Lake Baikal to Northeast China, influenced the decadal intensification of winter precipitation over the TRS via inducing the abnormal convergence of water vapor flux. In addition, the warm SST anomalies in the Indian Ocean may also have influence on the interdecadal variations of winter precipitation over the TRS region by affecting the south branch trough.

      • CHI Yanzhen, ZHENG Weipeng, WANG Yanming, HE Fen, BAO Ruijuan

        Available online:June 15, 2022  DOI: 10.3878/j.issn.1006-9825.2204.21188

        Abstract:Based on the daily observation data of 66 weather stations in Fujian Province from 1960 to 2020, the PDO monthly index, the ENSO monthly index and the NCEP/NCAR daily reanalysis data, the multi-scale features and impact factors are discussed by using the power spectrum analysis, wavelet decomposition, correlation and composition analysis. The results reveal: (1) there were 114 persistent cold events during 1961 to 2020. These events occurred frequently with stronger mean intensity before the mid 80’s of 20st century, however, decreased significantly with weaker mean intensity after that period. The prevalent duration was 5~11 days even up to 40 days. (2) the winter cold index exists significant 10-20-day and 30-60-day low frequency periods also 2-8 years in interannual scale. (3) the persistent cold events in winter are closely related to the ENSO events, the atmospheric intraseasonal oscillations and the cold air activities. PDO and ENSO in the negative phases were favorable for the occurrence and duration of persistent cold events. When the tropical convection prevailed in the maritime continent and the western Pacific Ocean, the persistent cold event occurred frequently. Furthermore, the cold northerly airflow guided by the strong Siberian High could reach the southern region of South China, that triggered the persistent cold event in Fujian province.(4)By comparing the persistent cold events with different durations, the “short”, “medium”and “long”events are characterized by the west, east and middle cold air paths, respectively.

      • Yang Chenyi, Cao Xiaozhong, Guo Qiyun, Yuan Yuan

        Available online:June 15, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21103

        Abstract:Based on the round-trip radiosonde data of Anqing, Changsha, Ganzhou, Nanchang, Yichang and Wuhan from June 2, 2018 to November 14, 2019, the turbulent layer thickness, logarithmic turbulent dissipation rate, Thorpe scale and buoyancy frequency are calculated by using Thorpe analysis method, and the probability, horizontal and vertical distribution characteristics are extracted. These radiosonde data have high observation accuracy, and the vertical resolution is about 6-10 meters, extending to about 30 kilometers, which can estimate the turbulence in the whole troposphere and lower stratosphere. Based on the turbulence feature extraction, this study carried out research and analysis, and compared the differences between different stations and the differences between the ascending and descending sections. The number of turbulent stratification in the troposphere is slightly more than that in the stratosphere, and the maximum turbulent layer thickness is also slightly larger. The number of turbulent stratification in the ascending section is slightly more than that in the descending section. The logarithmic turbulent dissipation rate has two modes, which decrease to both sides with the peak centers around - 35 and - 5 respectively. The troposphere is more concentrated in the peak center than the stratosphere, and the value of the peak center of the troposphere is slightly larger than that of the stratosphere, which indicates that the turbulence in the stratosphere is relatively weaker than that in the troposphere. From the horizontal and vertical distribution and configuration of logarithmic turbulence dissipation rate, Thorpe scale and buoyancy frequency, it can be seen that the turbulence intensity is higher at the position with larger Thorpe scale and lower buoyancy frequency.

      • WANG XIQIAO, LI JIANYING, LI SHUNGLIN

        Available online:June 14, 2022  DOI: 10.3878/j.issn.1006-9895.2204.21228

        Abstract:The daily high-resolution gridded station-observed precipitation and temperature and NECP Ⅱ atmospheric reanalysis datasets for the period of 1979 to 2020 were used to investigate the decadal variation of the 30~60-day boreal summer intraseasonal oscillation (BSISO1) over the Asian summer monsoon region and its influence on precipitation and temperature over eastern China. On the decadal timescale, BSISO1 is strong during the period of 1997~2008 (labeled as P1 episode), while the amplitude of BSISO1 is relatively weak during the period of 2009~2018 (labeled as P2 episode). During the P1 episode, BSISO1 has significant impacts on precipitation and temperature over the Yangtze?Huai River Basin (YHRB), but its influence over the southeast China is weak. However, the impact of BSISO1 on the precipitation and temperature over the YHRB is strongly weakened during the P2 episode; in contrast, its influences on precipitation and temperature over the southeast China become significant. During the P1 episode, BSISO1-related suppressed (active) convection anomalies propagate coherently from the equatorial western Pacific to the South China Sea?western North Pacific, inducing the vertical cell between the South China Sea and YHRB, leading to anomalous ascents (descents) and low-level moisture convergence (divergence) over the YHRB, thus favorable for intraseasonal positive (negative) rainfall anomalies and temperature decrease (increase) locally. Compared with P1, the seasonal-mean background humidity over the YHRB strongly weakens during the P2 episode, leading to decreased vertical transport of BSISO1-related circulation to seasonal-mean moisture, thus resulting in weaker intraseasonal fluctuations of rainfall over the YHRB. Note that the BSISO1-related suppressed (active) convection anomalies could shift further northward to the southeast China during the P2 episode, and the accompanied descents (ascents) cause the negative (positive) rainfall anomalies locally. Meanwhile, the adiabatic heating (cooling) in association with the anomalous descents (ascents) results in the positive (negative) temperature anomalies over the southeast China. Therefore, the compound extreme events in terms of persistently heavy rainfall over the YHRB accompanied with persistently heat wave over southeast China is more likely to occur during the P2 episode.

      • Li Mengdi, Qi Youcun

        Available online:June 14, 2022  DOI: 10.3878/j.issn.1006-9895.201.2201

        Abstract:Precipitation products with high spatial and temporal resolution and high accuracy are important for the observation of extreme precipitation as well as disaster prevention and mitigation. Gauge station observations provide accurate point-scale precipitation, but are insufficient for finely capturing spatial information on heavy precipitation induced by severe convection. Radar scanning can provide accurate precipitation information with high spatial and temporal resolution, but the accuracy of radar quantitative precipitation estimation (QPE) is vulnerable to various factors such as observation accuracy and Z-R relationship. Therefore, a Radar-Gauge Merging algorithm is proposed in this paper to combine the advantages of gauge station observations and radar QPE. The algorithm includes three steps: Kriging interpolations of precipitation, Local Gauge-Corrected(LGC)Radar QPE and Radar-Gauge Merging QPE. First, the precipitation interpolation fields are obtained by the Kriging method based on the regional station observations. Then based on the Local Gauge-Corrected method, the accuracy of the radar QPE is improved by making systematic corrections. Finally, combined with the precipitation type, the Radar-Gauge Merging QPE with high spatial and temporal resolution and high accuracy is produced by the Radar-Gauge Merging algorithm. Three extreme precipitation events: the 21·7 extreme precipitation in Zhengzhou, Typhoon In-Fa and the extreme precipitation in Suizhou in August 2021 are used to evaluate the performance of the Radar-Gauge Merging algorithm. The results show that the new Radar-Gauge Merging QPE outperforms the radar QPE product in terms of accuracy and characterizes the structure of precipitation more finely than the Kriging interpolations of the observation from the gauge stations in terms of spatial distribution of precipitation for the different extreme precipitation events and different time periods of precipitation events. It demonstrates the high accuracy and stability of the new Radar-Gauge Merging algorithm as well as its ability for capturing the distribution of extreme precipitation.

      • Lin Yihua

        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.

      • Lin Yihua

        Available online:June 14, 2022  DOI: 10.3878/j.issn.1006-9895.2203.22004

        Abstract:Rayleigh-Kuo theorem and Fjortoft theorem provide necessary conditions for barotropic instabilty of a geophysical fluid flow. Moreover, the barotropic instability of the geostrophic flow is of special importance for the geophysical flow. In this paper, two modified necessary conditions for the barotropic instability of the geostrophic flow are obtained. Based on energetics and potential vorticity dynamics theories, the implication of the necessary conditions for barotropic instability is explained. For the geostrophic flow, the Rayleigh-Kuo theorem can be revised as follws: A necessary condition for barotropic instability of the geostrophic flow is that the potential vorticity of the flow should have an extreme point. The Fjortoft theorem correspondingly becomes: A necessary condition for barotropic instability of the geostrophic flow is that Qy(U-Us)>0 in the field of the geostrophic flow, where ys is a point at which Qy=0 and Us=U(ys). That is, the absolute vorticity in the original theorems is modified to potential vorticity. These results are the consequence of geostrophic constraint and potential vorticity constraint. The energy relationship is the energetics requirement for the possibility of barotropic instability, the Rayleigh-Kuo theorem is the potential vorticity dynamics condition for the possibility of barotropic instability, and the Fjortoft theorem is the coordination of the two requirements of energetics and potential vorticity dynamics. For possible barotropic instability, all three requirements must be met.

      • wanghui, Ma Zhanshan

        Available online:June 14, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21265

        Abstract:During the Spring Festival in February 2018, the persistent heavy fog occurred in the Qiongzhou Strait, causing a large number of ships to stop sailing. Synoptic causes for heavy fog occurred from February 18 to 20 in 2018 are analyzed by using Himawari-8-derived sea fog products, observed visibility data gathered from coastal stations over Qiongzhou Strait and Final Operational Global Analysis (FNL) from National Centers for Environment Prediction (NCEP). Based on the high-resolution numerical model Global and Regional Assimilation and Prediction System (CMA-MESO), sensitive experiments are conducted from the perspective of comparing multiple boundary layer schemes, vertical resolutions of model and algorithms related with visibility of sea fog. It was found that the offshore sea temperature in South China during the heavy fog is lower than average. Affected by the supplemented weak cold air by the cold high pressure southward, the warm and humid air in the east flows through the cold sea surface and condenses quickly. The results of contrast experiments demonstrated that the prediction skills of visibility could be significantly improved by employing the Yonsei University (YSU) boundary layer scheme and sea fog diagnosis scheme of National Oceanic and Atmospheric Administration (NOAA) Forecast Systems Laboratory (FSL) along with increasing vertical levels of boundary layer. Compared to the MRF (Medium Range Forecast Model) boundary layer scheme, the simulations of both spatial distribution of heavy fog and the occurring time of minimum visibility are much better by using the YSU boundary layer scheme. Meanwhile, expanding the levels of lower layer of numerical model will be conducive to promote the simulations about the evolutions of low visibility. Based on the well predicted moisture and temperature, the predictions of visibility using FSL method are much more accurate.

      • WANG Dan, YU Zhenshou

        Available online:June 13, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21259

        Abstract:This study used the Weather Research and Forecasting Model WRF V4.0.2 (Weather Research and Forecasting Model, Version 4.0.2) to simulate two Meiyu front precipitation processes in Zhejiang Province, and to investigate the influence of different cumulus convective parameterization schemes on precipitation forecast. The WSM6 and Thompson microphysics schemes, YSU and MYJ boundary layer schemes, and 11 cumulus convective parameterization schemes were selected for comparative analyses to explore the influence of different cumulus convective parameterization schemes on Meiyu front precipitation forecast. The results show that: (1) In the process of precipitation forecast evaluation for each experiment, both the traditional point-to-point method and the neighborhood method can objectively show the prediction level of each experiment. However, the neighborhood method performs more objectively evaluation of the prediction level of small-scale heavy precipitation. (2) Three types of cumulus convection solutions (no cumulus clouds, traditional cumulus convection, and the scale-aware cumulus convection) can better simulate the light precipitation, but with the intensification of precipitation to ranstorm and heavy rainstorm, the scale-aware cumulus convection schemes improves the forecast results significantly. (3) The scale-aware cumulus convection scheme is more sensitive to microphysics and planetary boundary layer schemes, and the simulation results of the scale-aware cumulus convection scheme are more significant under different microphysics and boundary layer combination schemes, while the simulation results of the traditional cumulus convection scheme are not obvious. (4) In the "gray zone" range of 1-10 km, the scale-aware cumulus convection scheme can significantly improve the prediction results of model compared with the traditional cumulus convection scheme when the grid resolution is increased to 1 km. To some extent, the results of this study can provide a reference for the application of scale-aware convective parameterization schemes in high-precision operational forecasting.

      • DONG Shaorou, LIN Ailan, DONG Yantong

        Available online:June 13, 2022  DOI: 10.3878/j.issn.1006-9895.2204.21123

        Abstract:This study investigates the general circulation and external forcing factors which synergistically impact interannual variation of regional persistent high-temperature events in South China (RPH) during summer. Several observational datasets for nearly 60 years from meteorological stations and the NCEP/NCAR Global Reanalysis Data are used. The RPH index is defined based on historical processes of regional persistent high temperature in South China. Under the control of anti-cyclone throughout the troposphere, deep atmospheric dynamics and thermal anomalies occupy vertically over South China during the years with high RPHs. The interannual variation of RPH of South China is also closely relative to eastward-propagating wave trains over Eurasia and large circulation anomaly in the tropics due to the joint influence of sea surface temperature anomaly (SSTA) from tropical Indian Ocean, tropical Pacific and North Atlantic. The generation of anti-cyclone anomaly over South China Sea-western Pacific, which leads to the westward extension of strengthened western Pacific subtropical high, is resulted from the SSTA of tropical Indian Ocean and tropical Pacific. Meanwhile, the enhancement of wave trains over Eurasia in the upper troposphere, which leads to the eastward extension of strengthened South Asia high, is resulted from the SSTA of North Atlantic. Thus, strong descending is generated under the control of anti-cyclone throughout the troposphere over South China with combined effect of these key regions of oceans. And the high RPH is resulted from this strong descending which brings both adiabatic heating and strengthened solar radiation heating at the surface.

      • XIE Zuowei, BUEH Cholaw, ZHUGE Anran, LIAN Ruxu, LIAO Zhenyang, YAN Jie, LIN Dawei

        Available online:May 31, 2022  DOI: 10.3878/j.issn.1006-9895.2205.22039

        Abstract:This study uses rain-gauge observation data, the fifth reanalysis dataset of the European Centre for Medium-Range Weather Forecasts, and the piecewise quasi-geostrophic potential vorticity (QGPV) inversion to mainly investigate the intensification of warm and moist convey belt of Asian summer monsoon in the “21.7” Henan rainstorm and its key circulation. The result shows that the continually westward extension of the subtropical high covered eastern China, in whose southwestern flank broad southwesterlies transported not only warm and moist air mass but also high QGPV over Henan to northwestern China. Meanwhile, in northwestern China, the sensible heating of the Alxa Plateau maintained and deepened the local thermal low, which generated high QGPV anomalies in the near-surface layer of the low pressure center and the middle and low troposphere (750–650 hPa) over the Hetao area. As a result, such high QGPV formed an extensive high QGPV with the low pressure circulation over Henan, which yielded an extensive confrontation with the subtropical high. The QGPV inversion results show that such meteorological circulation pattern in the middle and lower troposphere intensified the southerly wind over Henan. The amplified southerly effectively transported hot and humid air mass to the Henan region, which was one of the key factors for the extreme downpour on 20 July. The southerly over Henan on 20 July is primarily contributed by the subtropical high with secondary contributions from the positive QGPV anomaly at middle and low troposphere over Hetao, while the contribution of the local low pressure circulation over Henan is slightly smaller.

      • Cui Xiao-Peng

        Available online:May 13, 2022  DOI: 10.3878/j.issn.1006-9895.2203.22016

        Abstract:Extreme rainstorms occurred in some regions of Henan Province during July 19 to 22, 2021 (referred to as "21?7" Henan rainstorm), causing severe urban waterlogging and casualties. With the help of precipitation observation data and reanalysis data, the large-scale circulation situations of this heavy rainfall were analyzed. Using the Lagrangian trajectory tracking model (FLEXPART) and the areal source-receptor attribution method, we also examined the moisture sources, transport paths and quantitative contribution of each source area. The results showed that the 500-hPa circulation in East Asia was extremely stable during the rainstorm and several days before the rainstorm. Connected with the northern high-pressure ridge, the western Pacific subtropical high pressure (referred to as the sub-high) was unusually northward, less moving. Meanwhile, the Eurasian high trough was westward, as well as the circulation in the middle and high latitudes of East Asia was significantly flat. During the rainstorm process, tropical cyclones "In-Fa" and " Cempaka" continued to have synergistic effects with sub-high, establishing obvious water vapor transport channels and providing sufficient moisture. The rainstorm areas in Henan province retained considerable near-surface wet region and high precipitable water. Tracking forward for several days, it was found that the target particles in the rainstorm area mainly came from the northwest Pacific Ocean, the South China Sea and other places, and were located at relatively low atmospheric levels. Additionally, a few particles which could be tracked back to the vicinity of the Sea of Japan and central Eurasia were at relatively high altitudes. The quantitative contribution analyses indicated that the moisture primarily originated from the continent of east-central China south of Henan (D) and the northwest Pacific Ocean (F), with the contribution of the former (52.59%) more than twice that of the latter (25.51%). In addition, the moisture from Henan storm area (T, 3.68%), the Indo-China Peninsula–South China Sea (E, 3.32%) and the Asian continent north of storm area (B, 2.28%) also played a role. The water vapor uptake of the target particles was the largest in region D, which was slightly higher than that in region F, but the rate of moisture loss along the former was clearly lower than that of the latter, resulting in significantly higher moisture contribution in region D than region F. Although the moisture intake in region B was somewhat higher than in region E, the sum of the moisture loss along the way and the unreleased part was higher than the latter, leading to a greater moisture contribution in region E. Moreover, region T had non-negligible precipitation recycling rate. When extending the number of days of forward tracking, the trajectories of target particles, water vapor uptake and contribution rate of each source had relatively little change, but the total contribution of moisture from all source areas significantly increased. Thus, it is of vital importance to extend the number of days for the tracking of moisture sources for heavy precipitation events like this extreme rainfall in Henan.

      • guoli, zhu cong wen

        Available online:May 09, 2022  DOI: 10.3878/j.issn.1006-9895.2204.21260

        Abstract:Tibetan Plateau (TP) is regarded as the “Chinese Water Tower”. Interaction between the westerly and monsoon flow around TP has an important impact on Asian climate. Based on atmospheric reanalysis dataset during 1981–2020, the coupling modes of seasonal cycle component of westerly-monsoon flow over TP are extract by empirical orthogonal function (EOF) method, and their seasonal variation characteristics are analyzed. It is found that the first mode accounts for 78.39% of total variances, which mainly reflects the seasonal cycle characteristics of East Asian monsoon, South Asian monsoon and mid-latitude westerly wind, as well as their interannual variation in each season. In summer, easterly winds prevail on TP and the southern side of TP at upper troposphere, ranging from 5° to 35°N. At the same time, lower troposphere is characterized by a typical cyclonic monsoon circulation around TP, and the tropical and subtropical areas are controlled by the southwest monsoon. The circulation structure in winter is opposite. The transit timing from winter (summer) to summer (winter) of this mode is basically consistent with the onset (ending) of East Asian and South Asian summer monsoon. On the interannual timescale, the enhancement of coupling mode is correlated with the intensity of East Asian monsoon and South Asian monsoon, as well as the northward movement of westerly in each season. When the coupling mode is weak, the monsoon and westerly show opposite characteristics. El Ni?o-Southern Oscillation (ENSO) is the key external forcing that affects the interannual variation of the westerly-monsoon coupling mode. Its impact is strengthened in summer, autumn and the following summer, while weakened in winter and the following spring of La Ni?a event. The second coupling mode of westerly-monsoon is characterized by the coordinated variation of easterly wind over TP and westerly wind in the south of TP at upper troposphere, and the southwesterly in South Asian monsoon region and anticyclone in the Northwest Pacific at lower troposphere. The variance contribution rate of this mode is 4.68%, showing obvious interannual variation and a significant weakening long-term trend, especially in winter.

      • Li Siyuan, GUO Xueliang, REN Jing, TANG Jie, QI Peng

        Available online:May 09, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21257

        Abstract:Using the data of the Second Tibetan Plateau Scientific Expedition and numerical simulation results with five-nested domain and high resolution of 333m of WRF model, the role of local mountain-valley wind circulation in an orographic clouds and precipitation event on 17-28, September 2019 in Nyingchi region of southeastern Tibetan Plateau is investigated. The results show that the precipitation event was caused by a passage of westerly trough and Nyingchi station is located at the base of westerly trough with weak unstable stratification. The orographic clouds and precipitation event is found to have obvious three-stage variations in the afternoon, evening and night, and the local mountain-valley wind circulation has an important role in the variation. In the afternoon, the strong solar radiation heating forms obvious upslope winds in the sunny slope firstly, and produces the strong upvalley winds, which are blocked and lifted in the windward slope, and induces strong mountain waves, and strong convective clouds and precipitation. In the evening, the strong longwave radiation cooling forms obvious downslope winds and cause the convergence and lifting process of warmer air in the valley, enhancing the formation and development of weak convection and stratiform clouds on the valley. In the nighttime, the downslope winds reach the strongest, and downvalley winds (mountain winds) are further enhanced, and the strong lifting causes deeper stratiform clouds. The convective clouds in the afternoon have more graupel particles and the main rain sources are from warm rain and graupel melting processes. The snow is very few. However, the similar cloud microphysical properties can be found in the evening and nighttime, the snow become dominant and the main rain sources are from snow melting and warm rain processes.

      • YUAN Yuan, SHEN Lelin, YAN Hongming, HONG Jieli

        Available online:May 09, 2022  DOI: 10.3878/j.issn.1006-9895.2204.21222

        Abstract:During the winter of 2020/2021, strong cold air processes broke out frequently in East Asia, which caused persistently low temperature, strong wind, heavy snow and rainfall, as well as serious impacts on people’s production and life in China. Using daily atmospheric circulation grid data and station temperature data, this paper revealed the low-frequency characteristics of the Siberian High (SH) and its significant impact on the three strong cold surges in China (Dec 13-15 2020, Dec 29 2020-Jan 1 2021, and Jan 6-8 2021). Both the SH and the temperature in eastern China showed significant quasi-biweekly (10-30d) and 30-60d low-frequency oscillation (LFO) features, which were stronger in the earlier winter than in the later winter of 2020/2021. However, the specific LFO features were totally different among three cold surges. In the first one, the quasi-biweekly oscillation had a significant positive contribution, while the 30-60d LFO showed a negative contribution. However, the second and third cold surges had a combined effect of quasi-biweekly and 30-60d LFO. In particular, the third one was in the strongest period of the above two LFO waves, which also lead to the largest cooling range and the widest range of low temperature in China, and the strongest development of SH. The enhancement of the quasi-biweekly SH had a significant impact on the cold air outbreak and the strong cooling in eastern China by about one pentad (5 days) ahead, with its impact on the cold air outbreak (low temperature in eastern China) the most significant by 1-2 (2-3) days earlier.

      • ZHENG Yanxin, LI Shuanglin

        Available online:May 09, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21154

        Abstract:Based on historical experiments of Coupled Model Intercomparison Project Phase Six (CMIP6), 22 models are systematically evaluated by Comprehensive Rating Metrics (MR). Then 10 models (GFDL-CM4, EC-Earth3, MIROC6, etc.) with reliable performance are chosen to project summer rainfall in the Yangtze River Basin in the future 30 years (2021-2050) under SSP245 and SSP585. The results suggest the total rainfall amount (PRCPTOT), and rainfall intensity (SDII) are projected to be relatively an increased trend by comparison with that in 1981-2010, and the large increase is located in the upper plateau and the middle-lower plains. In contrast, the occurrence of rainfall (R1mm) shows a little change because of opposite signal in upper and middle-lower reaches. The heavy rainfall (R95p) is projected to increase by 9.6% and 16.5% (SSP245 and SSP585), and extreme rainfall (R99p) is projected to increase by 10.2% and 15.5%. The maximum 5-day rainfall (RX5day) also exhibits an enhanced signal. Besides, the maximum consecutive dry days (CDD) will increase especially in upper reaches. As for different SSPs, the changes in SSP585 are greater than those in SSP245. These indicate there will be not only more rainfall amount and more occurrences of heavy-extreme rainfall events, but also a larger potential increase of droughts. Particularly, an increasing risk of the extreme rainfalls and floods in the middle and lower reaches and drought in the upper reaches deserve more attentions.

      • RAO Chenhong, BI Xinxin, CHEN Guanghua, 喻自凤

        Available online:April 29, 2022  DOI: 10.3878/j.issn.1006-9895.2204.21255

        Abstract:This study uses the WRF model to numerically simulate the influence of the offshore Typhoon In-Fa and Typhoon Cempaka on the extreme rainstorm process in Henan from July 19 to 21, 2021. The control experiment (CTL) reasonably captures the tracks and intensities of the two typhoons, the large-scale circulation pattern, the intensity and spatial distribution pattern of the rainstorm event in Henan, which basically reproduce the extreme rainstorm process in Henan. In addition, the sensitivity experiments indicate that after the removal of the Typhoon In-Fa, the subtropical high extends southward and forms the southeast wind jet in the south, causing the south (east) wind component to get weakened (strengthened) around Henan. The water vapor transport in the zonal direction gets dominant, which is conducive to the transition of the rainfall distribution from the south-north orientation in the CTL to the east-west orientation. On the other hand, due to the southeast wind at the low level is weaker than the easterly jet before the removal of the Typhoon In-Fa, the local convergence at Henan rainfall area is weakened, and the net water vapor flux is reduced by 5.81% compared to the CTL experiment. The slowdown in westward movement of the mid-latitude cold air causes the reduction of the local equivalent potential temperature gradient. Therefore, the rainfall intensity in the NOINFA is relatively weaker than that in the CTL. After the removal of Typhoon Cempaka, the large-scale circulation characteristics are almost unaffected, and the water vapor transport on the south side of Henan is slightly weakened. Therefore, the distribution of heavy rainfall is basically similar to that in the CTL, with a slight decrease in rainfall peak. Compared to Typhoon In-Fa, Typhoon Cempaka has less effect on the rainstorm event in Henan.

      • Ding weiyu

        Available online:April 26, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21176

        Abstract:Abstract: Cloud is closely related to high impact weather. Satellite infrared radiances data provides a lot of information in cloudy area. However, the observation operator error caused by the initial cloud parameters errors and the nonlinear influence of cloud on radiation process is too large, and the error distribution is non Gaussian, which brings difficulties to the direct assimilation of satellite infrared data in cloudy conditions. Aiming at the key technical problems of direct assimilation of satellite infrared radiances data in cloudy conditions, this paper reviews and summarizes the research progress of assimilation methods, radiation transfer mode, control variables, background errors, cloud detection, observation errors setting and bias correction at home and abroad in recent 20 years. The results show that the trend of direct assimilation of satellite radiance data is to further supplement the cloud and rain information and improve the corresponding technology based on clear sky radiance assimilation technology, so as to realize the direct assimilation of satellite data under “all-weather” conditions. It is pointed out that the direct assimilation of satellite infrared radiances in cloudy conditions faces challenges in how to construct the control variables related to cloud parameters and their background errors, and how to eliminate the nonlinear influence of cloud on observation and observation operators. With the common development of observation technology, assimilation technology and model technology, satellite infrared radiances data will inevitably play a greater role in the field of numerical weather prediction. Key Words: cloudy condition;satellite infrared radiances; assimilation

      • Li Xiao Xia, Zhang Yu Xiao, Cao Xiao Zhong

        Available online:April 14, 2022  DOI: 10.3878/j.issn.1006-9895.2112.20247

        Abstract:In this study, multiple-source satellite data, high frequency data directly measured by marine meteorological drift buoy, Argo floats data and HYCOM analysis dataset were used to analyze the temporal and spatial variation of Sea Surface Temperature (SST) and vertical sea water temperature profile during the process of super typhoon Lekima(1909). The results showed that the maximum SST decrease could reach above 5℃ after “Lekima”, the cooling area was more concentrated on the right side of typhoon’s track. “Lekima” resulted in the vertical mixing of near surface water and subsurface water column, and subsurface water column was heated, which increased the depth of the mixed layer and temperature of the deep water. According to the data mentioned above, it was found that the emergence of main SST decreased region was 1-2 days later than the appearance of “Lekima” center area. Among all data, marine drift buoy data could describe the variation in SST more accurately, and could be used as a reference to verificate satellite data, as the drift buoy could directly measure SST in high frequency. Moreover, the cooling effect in different marine region also depended on the marine environment. When “Lekima” was closer to Kuroshio, the cooling effect was concentrated in the mixed layer. On the contrast, when “Lekima” was far from Kuroshio, the cooling effect could extend to the thermocline.

      • Yao Binbin, Shi Chunhua, Guo Dong

        Available online:April 14, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21254

        Abstract:Stratospheric Arctic vortex (SAV) anomalies can afford indications to extreme weather and Arctic ozone losses in winter and spring. The SAV in early spring is found to be related to the second mode of the interannual sea surface temperature (SST) in the Tropical Pacific in 1979-2020, the spatial pattern of SST anomalies in the western equatorial Pacific from the ERA-5 reanalysis data. The specific progress of the western equatorial Pacific SST anomalies affecting the SAV is revealed by the CAM5 numerical simulations. The SST warming in the western equatorial Pacific in winter and spring can intensify local deep convective precipitation. Then the anomalous latent heating induces a Rossby wave (high pressure anomalies in the upper troposphere) to its northwest side through the Matsuno-Gill atmospheric response. The Rossby wave adjusts the strength and position of the strongest trough-ridge system of the Northern Hemisphere in the North Pacific along the great circle path, leading to a decrease of the amplitude of wave 1 of the meridional wind and an increase of the phase difference of the wave 3 between the meridional wind and temperature, which results in less wave activity fluxes of the wave 1 and wave 3 propagating to the stratosphere. Finally, the less poleward transport of eddy heat flux enhances the SAV in spring.

      • guoziwei, wanglijuan

        Available online:April 14, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21215

        Abstract:Using the daily reanalysis data of ERA5 and the daily stations data of precipitation provided by the China Meteorological Administration, the influence of the “combined modality” of the Silk-Road Pattern(SR) and the East Asia-Pacific Pattern(EAP) teleconnection on the heavy precipitation in the early stage of Meiyu in the Yangtze-Huai River region in 2020 is analyzed, it shows that the “combined modality” can trigger continuous precipitation in the Yangtze-Huai River region. At the beginning of June 2020, the negative-phases SR(Silk-Road) and the positive-phases EAP(East Asia-Pacific) appeared at the same time, and the phase difference reached the maximum value in June. The synergy of the two lead to an abnormally early time for the Meiyu in 2020. The main manifestations are as follows: (1) The negative-phases SR causes the acceleration of the westerly jet, which promotes strong high-level divergence over the Yangtze-Huai River region on the south side of the jet stream entrance area. (2) The negative-phases SR is conducive to the eastward movement of the South Asian High, and the positive-phases EAP is conducive to the westward movement of the Western Pacific Subtropical High, and the two move towards each other. The negative-phases SR and the positive-phases EAP had the largest difference on June 9. At this time, the South Asian High and the West Pacific Subtropical High overlapped at about 120°E, which is conducive to continuous precipitation in the Yangtze-Huai River region. (3) There is a pair of anomalous “cyclone-anticyclone” circulations related to the positive-phases EAP in the middle and low latitudes of low-level East Asia, which makes the low altitude (20~35°N, 100~125°E) prevailing strong southwest airflow. The northerly airflow at mid-latitudes is conducive to the transportation of dry and cold air to the south. It merges with the warm and humid southwest airflow over the Yangtze-Huai River region, bringing about strong water vapor convergence and making the local upward movement of the atmosphere more intense.

      • Fu Shiyi, Shi Ning, Zhang Dongdong

        Available online:April 14, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21238

        Abstract:Based on the daily reanalysis data of the Japan Meteorological Agency (JRA55) from 1958 to 2019, the thermodynamic characteristics of the warming process before the summer onset (from pentad 19 to pentad 28) over North Asia are studied based on the thermodynamic equation. The results show that diabatic heating and temperature advection alternatively dominate the temperature tendency before the summer onset over North Asia. Interestingly, these two terms show an opposite trend to each other. Before pentad 22, adiabatic advection of climatological mean temperature dominates the warming process over North Asia. After that, however, the diabatic heating becomes enhanced gradually while the adiabatic advection process weakens gradually, making the diabatic heating become the dominant term. Based on the linear baroclinic model, the numerical results reveal that the diabatic heating over the mid- and high latitude Eurasia can not only heating the local air masses aloft, but also force a cyclonic circulation and upward motion. The circulation responses are favorable for the southeastward movement of the low pressure system which originally locate around Novaya Zemlya toward North Asia, leading to the formation of cold advection in both the horizontal and vertical directions. The cold advection counteract partially the local diabatic heating, forming the steady warming process over North Asia.

      • Chen Junjie, Sun Jilin

        Available online:April 14, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21085

        Abstract:Based on NOAA (National Oceanic and Atmospheric Administration) monthly OLR data during 1979 to 2019, NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis), ECMWF (European Centre for Medium-Range Weather Forecasts) ERA5 monthly reanalysis datasets, and East Anglia CRU (Climatic Research Unit) surface temperature data during 1960 to 2019, the effects of El Ni?o events with anomalous convection at different zonal position on regional climate are discussed. The results show that: Studying the effects of El Ni?o events on atmospheric circulation and regional climate anomalies based on the zonal position of tropical Pacific anomalous convection can avoid the limitation that SST anomalies cannot reflect the atmospheric convection anomalies fully. The anomalous convection is located near 140°W in Super El Ni?o events. Anomalous subsidence over tropical western and eastern Pacific is eastward, resulting in higher temperature and drought in northeastern Australia, northeastern Brazil, and more rainfall along the coasts of Peru and Ecuador during boreal autumn and winter. The PNA (Pacific-North American) wave train is located eastward, which significantly weakens the North American trough and brings warmer winter in North American. The geopotential height from Greenland to northwest Europe is low, making northern Eurasian significantly warmer. In Eastern El Ni?o, the anomalous convection is located near 160°W. Accordingly, anomalous subsidence is westward, causing dry northwestern Australia, northwestern South America and wet eastern Australia from boreal autumn to spring. The PNA wave train originates in south of Aleutian Islands and deepens the North American trough, causing severe cold winter in eastern North America. The anomalous convection is located near 180 ° in El Ni?o Modoki. Contrary to Super El Ni?o, the coasts of Peru and Ecuador is dry due to abnormal subsidence and most of Australia tends to experience drought from boreal autumn to spring under the controlled of anomalous anticyclone. The PNA wave train is located westward, resulting in severe cold winter in southeastern America. In the winter of Eastern and El Ni?o Modoki events, the Atlantic shows a negative NAO (North Atlantic Oscillation) pattern, and the temperature in the middle latitudes of Eurasian is low.

      • Yang Jiefan, 龚佃利, Wang Jun, 张佃国, 孙莎莎, 陈澍

        Available online:April 14, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21210

        Abstract:Based on the original backscattering signal of Micro Rain Radar and the RaProM algorithm, the equivalent radar reflectivity, the particle falling velocity and Doppler spectrum width are calculated after power spectrum calculation, noise removal and deblurring. Furthermore, the precipitation type are identified. Considering particles falling velocity, the equivalent radar reflectivity, particle size characteristics of different precipitation type and whether there is a bright band, RaProM algorithm can identify particle phase including snow, drizzle, rain, hail and mixed type. In addition, the liquid precipitation parameters, such as radar reflectivity factor and rain intensity, are calculated. Subsequently, three typical cases of stratiform cloud precipitation on July 2, 2021, rain-snow conversion on December 25, 2019, and gradually decreasing bright band height on March 4, 2018 are selected to verify and discuss the results. The method of precipitation type classification is applied to typical stratiform precipitation, the vertical structure shows snowflakes in the supercooled water area, mixed type precipitation in the ice-liquid conversion zone near the 0 ℃ layer and liquid precipitation below the bright band, which verified the validity of the method. The methods are further applied in precipitation type classification and bright band detection, and the results show that compared with standard inversion process of Micro Rain Radar, RaProM algorithm has the advantage of no assumption of precipitation type and considering the upward velocity of particles (such as snowflakes). The results of RaProM algorithm are in good agreement with the co-located microwave radiometer and cloud radar in the vertical structure, and the deviations from the ground disdrometer in the raindrop size distribution and rain intensity are reduced compared with the products of Micro Rain Radar.

      • ZHANG Zhiwei, GUO Fengxia, CHU Yu, ZOU Dike, LU Xian, WU Zeyi, LIU Zhou

        Available online:April 12, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21229

        Abstract:In order to further understand the characteristics of lightning activity during the whole life of TC, we used WWLLN data, TC best-track data from National Meteorological Center of CMA, TBB data from FY-4A satellite and ERA5 reanalysis data. We took the strongest typhoon "Mangkhut" that landed in China in 2018 as an example. The temporal and spatial distribution of lightning activity and its variation with intensity during the whole process from generation to extinction are studied, and the relationship between lightning activity and wind circle radius and underlying surface is discussed. The results show that: (1) The lightning activity in " Mangkhut " has obvious three-circle structure, with the highest density of lightning in the inner core, almost no lightning in the inner rainbands, and the largest amount of lightning in the outer rainbands. The main occurrence time of inner core lightning is different from that of outer rainbands lightning, which can also produce a large amount of lightning in the open sea. (2) The azimuthal distribution of lightning activity is closely related to TC intensity, geographical location and environment. The azimuthal distribution of lightning activity is different in different periods. (3) There is no clear relationship between lightning activity and wind circle radius. Lightning activity occurs in the southeast and southwest, where the wind circle has a smaller radius. (4) Before and after TC rapid intensification, the inner core lightning activity has a certain indicator effect on TC intensity intensification. In addition, there is a good correlation between lightning activity and convective intensity in the inner core. (5) The existence of islands and land plays an important role in the development of severe convection. When the stream hits higher terrain, it is forced to lift, forming lightning. The southwest direction of TC is about 300km away from the southeast side of the island, and there are sufficient water vapor, heat and more anthropogenic aerosols, which are conducive to the development of updraft, thus generating lightning. These understandings contribute to the application of lightning data in monitoring and early warning of mesoscale and small-scale severe convection in TCs.

      • Xuanhui ZHI, Haiming XU, Jing MA, Shiqun ZHI

        Available online:April 11, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21159

        Abstract:Based on the observed daily fog data from 52 meteorological stations in southern China and ERA5 reanalysis data from 1979 to 2016, effects of ENSO on the interannual variability of winter fog days over southern China and the interdecadal variation of the relationship between them are investigated using the EOF analysis and other statistical methods. Results are shown as follows: (1) The winter fog days over southern China (WFDSC) exhibit a whole-region consistent pattern and display evident interannual variability and significant increasing trend. The WFDSC is closely related to the weakened northerly wind, more stable atmosphere and the decreasing T-Td near surface, which implies that the water vapor in air is increasing, providing favorable meteorological background fields for the maintenance and development of fog over southern China. (2) There is a close relationship between ENSO and the interannual variability of WFDSC, which mainly depends on heavy fog days rather than light fog days. During El Nino winters, an anomalous anticyclone tends to occur over the Philippine Sea, and the warm moist anomaly southwesterlies on the western flank of this anticyclone brings abundant water vapor to southern China, conducive to the fog formation. Roughly opposite changes of fog days occur during La Nina winters. (3) The interannual ENSO-WFDSC relationship exhibits an obvious interdecadal change around 1996, with a low correlation during the period of 1979-1996 but a high correlation after 1997. A further analysis shows that this change in the relationship might be modulated by the Atlantic Multidecadal Oscillation (AMO).

      • ZHANG Zhe, QI Youcun, LI Donghuan, ZHAO Zhanfeng, CUI Liman, SU Aifang, WANG Xinmin

        Available online:April 11, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21237

        Abstract:Using the disdrometer observation data, we examined the raindrop size distribution (DSD) characteristics of the extreme rainstorm event on July 20th, 2021 in Zhengzhou. The performance of several radar quantitative precipitation estimation (QPE) methods was then evaluated using polarimetric radar data. Results revealed that during the peak rain rate period, the DSD showed a high number concentration and large mean particle size. During this event, the normalized intercept parameter was similar to those observed in other parts of China, but the mass-weighted diameter was significantly larger. Before the peak rain rate period, the DSD experienced dramatic change. As the mass-weighted diameter increased, the number concentration then followed, resulting in a rapid increase in the rain rate. Polarimetric radar data were used to calculate the hourly QPE rainfall during 08-09, July 20th, 2021 based on several QPE methods and QPE parameters, and then the performances of each method were evaluate against the gauge observation. Result showed the the cap of reflectivity-based estimator R(ZH) should be removed or raised, otherwise the rainfall would be significantly underestimated. What’s more, this estimator was sensitive to the QPE parameters. On the other hand, the specific differential phase-based estimator R(Kdp) was relatively insensitive the the QPE parameters, the accuracy of the specific differential phase was responsible for its performance. The best R(Kdp) estimator reached over 70% of the observational hourly rain fall, outperformed the best R(ZH) estimator during this extreme rainstorm event.

      • WANG Qilu, XU Wenwen, TU Jingyi, YU Shuyang, RAO Jian, GUO Dong

        Available online:April 11, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21156

        Abstract:Based on the monthly ERA5 reanalysis datasets, the study considers the mean flows and eddies in the stationary or transient transport by using the Lorenz circulation decomposition method. The purpose is to compare the dynamical transport characteristics of ozone over the Arctic and the Tibetan Plateau in detail. The results indicate that the effect of the dynamical transport is the strongest in the upper stratosphere of these two regions, which results in the reduction of ozone. Further analyses suggest that the effect of the stationary transport is stronger than that of the transient transport, and the zonal and meridional transports almost have the opposite effect. However, the intensity of dynamical transport over the Arctic is much greater than those over the Tibetan Plateau. The zonal transport over the Arctic results in the reduction of ozone in the upper and middle stratosphere and the increase of ozone in the lower stratosphere, while the effect of the meridional transport is opposite and much weaker. Both of them mainly function in the upper stratosphere. Over the Tibetan Plateau, the intensity of the zonal transport is the same as the intensity of the meridional transport. They almost have the opposite effect except for the top of the stratosphere, where both of them lead to the reduction of ozone. There are two centers with the strongest transport over the Tibetan Plateau, located in the upper stratosphere and the upper troposphere - lower stratosphere (UTLS) respectively. The differences of zonal and meridional transports over these two regions are mainly caused by the stationary transport by eddies. The differences between stationary and transient transports over the Tibetan Plateau are smaller than those over the Arctic. Furthermore, the transport of zonal mean ozone by eddies plays a dominant role in the stationary and transient transport. Consequently, the eddy transport exerts an indispensable influence on the dynamical transport of ozone over the Arctic and the Tibetan Plateau.

      • SHEN Dongdong, RAN Lingkun, YANG Shuai, LI Na, JIAO Baofeng

        Available online:April 11, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21252

        Abstract:In this study, by taking account of the complex topographic effect in Xinjiang and the condensation latent heat heating of the moist atmosphere near frontal rainstorm area, 1) we derive the thermodynamic frontogenesis functions under terrain-following coordinates based on the potential temperature, equivalent potential temperature and generalized potential temperature, and a dynamic frontogenesis function driven by the deformation field. The advantages of frontogenesis functions in terrain-following coordinate in studying frontal processes in in complex topographical region are expounded; 2)We discuss the advantages and disadvantages of the four frontogenesis from the perspective of the temperature and humidity gradient increase, which is the more essential process during a frontogenesis process, and find that the generalized potential temperature and deformation frontogenesis have a better correspondence with the precipitation process; 3) We perform numerical simulation of a frontal precipitation event by utilizing of WRF model, which propagate from north to south of Tianshan in Xinjiang, and carry out the analysis of the main forcing of the thermodynamic and dynamic frontogenesis functions, as well as their effect during the rainfall. The results suggest that dynamic frontogenesis plays an important role in precipitation triggering and weakening stage and is caused by energy conversion between vorticity, divergence and deformation. Thermodynamic frontogenesis mainly acts on precipitation development stage, and latent heating is the main forcing. In practical applications, the overlapping region of two frontogenesis functions in the near-surface layer and mid-lower troposphere could indicate the direction of future precipitation propagation.

      • zhang xing, Zhou Tianjun

        Available online:April 08, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21099

        Abstract:Based on observation and reanalysis data, we systematically evaluate global monsoon simulated by the new version of climate system model FGOALS-g3 by applying moisture budget diagnosis and composite analysis, and analyze the advantages and disadvantages compared with FGOALS-g2. Otherwise, the influences of air-sea coupling process on the simulated results are discussed by comparing with the corresponding atmospheric component model GAMIL. FGOALS-g3 reasonably reproduces the basic characteristics of climatology of global monsoon, including annual mean precipitation and circulation, annual cycle modes, monsoon precipitation intensity and monsoon region, but the model underestimates the annual mean precipitation over land monsoon region, overestimates the annual mean precipitation over ocean region, and the simulated spring-fall asymmetric mode of annual cycle is stronger in tropical monsoon region. The results show that the smaller land monsoon region than observation in FGOALS-g3 is associated with the weaker vertical moisture advection (especially the thermodynamic term) in summer. For the inter-annual variability, FGOALS-g3 can reproduce the drier pattern of global monsoon during El Nin ?o year. However, some biases in precipitation anomalies are exist in some monsoon regions. For instance, the precipitation in the West African monsoon region is more than normal, and the precipitation in the Southwest Indian Ocean is a dipole anomaly, both of which are inconsistent with the observation, and the precipitation in the Northwest Pacific monsoon region is more than the observation during El Nin ?o year. Because there is no weak convergence center in the upper layer of western Africa in the simulation, and the simulated maritime continent is warmer than observation, result in the convective center moves westward during El Nin ?o year. In comparison with FGOALS-g2, FGOALS-g3 improves the simulation of monsoon circulation, inter-annual variability of monsoon precipitation, and monsoon-ENSO relationship. Comparing the coupled and uncoupled simulation, most of the biases in the coupled model originate from the atmospheric model itself, and the air-sea coupling process partially improves the simulation of precipitation and circulation of Asian-Australian monsoon region and the tropical Indian Ocean, but the sea surface temperature bias caused by the coupled process enhances dry bias of the Indian Peninsula and the wet bias of the tropical Indian Ocean.

      • WANG MEIRONG

        Available online:April 08, 2022  DOI: 10.3878/j.issn.1006-9895.2204.21169

        Abstract:Based on historical observations at 77 meteorological stations and a long-term dataset of integrated land-atmosphere interaction observations on the Tibetan Plateau (TP) (2005-2016), the historical simulations from 12 models participated in the sixth Phase of the Coupled Model Intercomparison Project (CMIP6), and GEWEX-SRB satellite radiation products, we have quantitatively examined the ability of CMIP6 models in simulating the surface sensible heat flux over the TP during 1979~2014, and analyzed the possible causes of simulation biases. Results show that CMIP6 models can well reproduce the annual cycle and seasonal spatial patterns of the sensible heat over the TP, albeit with lower amplitudes than calculated sensible heat flux, especially showing obvious underestimation over the strong sensible heat regions. The area-weighted long-term spring sensible heat fluxes over the central and eastern TP simulated by 12 models are generally lower than calculated values, with the minimum sensible heat amplitude in MIROC6 which has approximately 1/3 of the climatological amplitude in calculated sensible heat flux. Further, we find that wind speed at 10 m and land-air temperature difference in spring simulated by models are stronger and weaker than calculated values, respectively, implying that the lower sensible heat amplitudes simulated by CMIP6 multi-models are mainly attributed to the cold biases of land-air temperature difference. Spatially, the cold biases of land-air temperature difference widely exist over the central and eastern TP, in which more specifically, both of surface temperature and air temperature show the cold biases, however, with colder biases in surface temperature. The cold biases mechanistically are likely related to the simulated stronger precipitation over the TP in CMIP6 models.

      • RUI Xue, LU Chunsong, YIN Yan, LV Jingjing, CHEN Kui, XUE Yuqi, WANG Yuan, XU Xiaofeng, WANG Jing

        Available online:April 01, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21138

        Abstract:In order to further improve the forecast accuracy of fog visibility, a new fog visibility diagnostic scheme was established and tested based on the observational data of fog microphysics from April to July in 2008, May to August in 2009, May to September in 2011 at the Bright Summit of Mount Huangshan, and January to March in 2009 in Enshi, Hubei Province. First, previously developed visibility diagnostic schemes were compared and the importance of considering both liquid water content and droplet number concentration was confirmed in visibility schemes. Second, the coefficients in the previous diagnostic schemes are often taken as constants, but the close relationship between these coefficients and microphysics was found in this study. The relationships between the fitting coefficients and the droplet number concentration were established by half of Mount Huangshan’s data in 2008 and the visibility diagnostic schemes were improved. The effect of the new scheme has been verified by independent data, which include the other half of Mount Huangshan’s data in 2008, the whole of 2009 and 2011 and Enshi’s data in 2009.

      • CHENG Jingjing, LI Qingqing, Chen Jinpeng

        Available online:April 01, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21216

        Abstract:The characteristics of cold pools in the outer core of tropical cyclones under vertical wind shear of different magnitudes are investigated based on high-resolution idealized numerical simulations. The results suggest that the convective and non-convective cold pools in the outer core exhibit similar characteristics in different vertical wind shear magnitudes. Both two types of cold pools exhibit potential temperature, equivalent potential temperature, water vapor mixing ratio deficits and positive pressure perturbations. The depth of cold pools in the outer core of tropical cyclones is mostly less than 400 m, and the average strength is approximately 4~6 m/s, which is much smaller than that in mesoscale convective system. The depth is deeper and the intensity is also stronger significantly for non-convective cold pools, indicating that the intensity of different types of cold pool is not only related to the potential temperature perturbation, but also depends on its depth. The cold pools are caused by widespread convective-scale downdrafts, and the downward vertical mass transport in convective cold pools caused by stronger downdrafts is almost twice that of non-convective ones. Budgets of surface perturbation pressure induced by downdrafts indicate that subcloud evaporational cooling and water loading are conducive to high pressure near the surface in cold pools, while in-cloud warming due to latent heat release leads to a pressure decrease. Moreover, the greater effects of precipitation drag and subcloud evaporation in convective cold pools result in more significant pressure increasement than that in non-convective cold pools. The features of both types of cold pools also varies with the increase in the shear value. There are mostly micro-scale and discrete convective cold pools in the weak-shear environment. As shear increases, the total number of outer-core cold pools and the frequency of convective cold pools decreases while the non-convective ones with larger range and mostly linked to dissipated convection increases, deepen and intensify, in addition. There are weaker outflow but stronger cyclonic velocity caused by both two types of cold pools with the shear magnitude increased.

      • Yanfei, Yang jiefan

        Available online:April 01, 2022  DOI: 10.3878/j.issn.1006-9895.2203.21180

        Abstract:The microphysical characteristics of Warm Conveyor Belt (WCB) within a Winter mesoscale snowstorm in southern Hebei were analyzed using aircraft observation data. Affected by the WCB associated with the Southwest Vortex Warm Front, the cloud can be divided into three layers in the early period of snowfall. There were a few small-size ice crystals in the upper part of the cloud. The thickness of the middle layer is equivalent to the thickness of the WCB (0.9km), in which the maximum liquid water content was 0.51g.m-3, with low concentration of ice crystals, and the vertical profile of liquid water content and adiabatic water content was similar. In the lower part of the cloud, the number concentration of ice crystal increased by two orders of magnitude, and the particle spectrum width increased significantly. The ice crystal habits were predominantly of column, bundle of column and graupel. Graupel particals were formed through the process of riming that occurred in the middle layer with abundant supercooled water, and a large number of columnar ice crystals were produced by the Hallett-Mossop mechanism. The abundance of supercooled water in the WCB had an extremely important influence on the microphysical processes during the early snowfall period. The vertical structure of the cloud was relatively uniform in the later period of snowfall, due to the jet at 700hPa had moved out of the observation area. At this time, the ice crystal habits were predominantly of plate, and the particle size increased as the height decreases, reflecting the growth of the ice crystal through aggregation process.

      • 李娜, Ran Lingkun, Jiao Baofeng

        Available online:April 01, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21245

        Abstract:In this paper, the organization process and mechanism of a rainstorm in the arid area of Western Southern Xinjiang are diagnosed and studied by using the potential vorticity (PV) wave-activity density and wave relation equation. The key physical processes affecting the organization of rainstorm convection system are analyzed and discussed in detail. The PV wave-activity density couples a variety of atmospheric dynamic and thermal disturbances affecting the evolution of convective clouds, which can well describe the organization process of convective system. On this basis, the wave relation equation describing the change of the PV wave activities can be used to study the physical factors driving the organized development of convective system. It is found that many physical processes diagnosed by the wave relation equation are related to the development and evolution of disturbed baroclinic, disturbed wind shear and disturbed vorticity, indicating that they play an important role in convective organization. During the organization process, multiple East-West oriented convective lines developed into a northeast-southwest banded convective system, including the maintenance of strong convection and the increase of North and South scale. The development and enhancement of the weak convection in the northeast direction of the convective line is related to the enhancement of the baroclinic disturbance caused by the thermal transport of the basic state flow from the strong convection area to weak-convection area. The key processes affecting the maintenance of strong convection in the middle of the convective line include: the thermal transport caused by updraft and downdraft which leads to the enhancement of baroclinic disturbance in the convective line, the cyclonic circulation formed by disturbed west wind and disturbed east wind which leads to the enhancement of meridional shear circulation, and the disturbed meridional wind transport of the disturbed zonal wind shear to the convective center, resulting in the enhancement of zonal shear and thus the enhancement of the vertical shear circulation. The study shows that the organization of the convection system is the result of the evolution and cooperation of various dynamic and thermal disturbances in the atmosphere. The key process can be clearly reflected through the wave activity evolution equation, the predictive significance of which for the organization of the convection system can be discussed in the future. Keywords: Southern Nanjiang, heavy rainfall, rainstorm organization, PV wave-activity density

      • Yan Li, Bin Chen, xiangde Xu

        Available online:March 24, 2022  DOI: 10.3878/j.issn.1006-9895.2202.22018

        Abstract:Based on atmospheric reanalysis and precipitation, together with the winter and spring snow data over the Tibetan Plateau obtained by gauged stations and satellites, this study compare and validates the consistency of changes in different snow data sets on interannual scale. The impacts of winter and spring snow anomalies on the frequency and intensity of summer precipitation over the Eastern China are further explored. Combined with the atmospheric physical diagnosis and numerical simulation, the possible causes of the spatial difference in the impacts of snow anomalies on summer precipitation in China are investigated as well. The result of this study shows that: 1) the variation of snow depth observed by gauged stations is well consistent with that derived from the satellite data on the interannual scale. 2) The impacts of Plateau snow anomalies on the frequency and intensity of summer precipitation in China exhibit significant spatial differences. When there is more snow in winter and spring on the Tibetan Plateau, the frequency of summer precipitation increases obviously in North China, the middle and lower reaches of the Yangtze River and Northeast China, whereas the increase of rainfall frequency in North China is mainly dominated by the types of moderate rain and light rain, contrasting to the increase of heavy rain frequency in the middle and lower reaches of the Yangtze River. 3) During the years of more snow cover, the heat source over the Tibetan Plateau is weakened, resulting in occurrence of "negative-positive-negative" abnormal wave train structure on the 500hPa potential height, the strengthened and southward westerly jet, and the southward subtropical high ridge. The anomalous cyclonic circulation on the north side of the anomalous anticyclone in the Northwestern Pacific enhance the water vapor transport residing in the middle and lower reaches of the Yangtze River Basin. With the strengthened atmospheric vertical movement, the intensity and frequency of heavy precipitation is increased in this region. However, the region of North China is controlled by the circulation structure of "saddle" field, the occurrence frequency of small precipitation increases significantly, but the water vapor transport is weak, and the changes in precipitation intensity is not significant.

      • ZHANG Shenglong, SUN Bo, CHEN Ping

        Available online:March 22, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21129

        Abstract:Based on the NCEP/NCAR reanalysis data, the ERA5 vertical integrated water vapor flux data and the NOAA monthly mean sea surface temperature (SST) data, the interdecadal variations of the relationship between the central and eastern tropical Pacific SSTs and the East Asian water vapor transport (WVT) in December and February during 1950–2019 are investigated. The results indicate that the correlation between the East Asian meridional WVT and the central and eastern tropical Pacific SSTs in December was weak before the mid-1980s and significantly positive after the mid-1980s. The correlation in February was significantly positive during 1950–70 and 1990–2010. The interdecadal variations of the relationship between the East Asian meridional WVT and the central and eastern tropical Pacific SSTs in December are partly due to the fact that the East Asian meridional WVT was mainly modulated by the Pacific–East Asian (PEA) teleconnection during 1986–2019. The circumglobal teleconnection in the Northern Hemisphere, which would induce an anomalous southerly WVT over East Asia corresponding to warm SST anomalies in the central and eastern tropical Pacific, is another mechanism to influence the interdecadal variations of the relationship between the two in December during 1986–2019. The above mechanism enhanced the effect of the PEA teleconnection. The interdecadal variations of the relationship between the two in February are due to the fact that the connection between PEA teleconnection and the East Asian meridional WVT was enhanced during 1950–70 and 1990–2010. Whereas, the East Asian WVT was modulated by the circumglobal teleconnection in the Northern Hemisphere in February during 1971–89,corresponding to the cold SST anomalies in the central and eastern tropical Pacific, which is another mechanism causing the relationship between the two to be insignificant during 1971–89. The above mechanism opposed the effect of the PEA teleconnection.

      • luowenjie, xiangjie, duhuadong

        Available online:March 22, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21096

        Abstract:GPS occultation detection technology, as an advanced atmospheric detection method, has been widely used in numerical weather forecasting, climate and space weather research. One of the problems in occultation detection is that it is easily interfered by the reflected signals on the earth"s surface. Identifying and separating the reflected signals in the occultation detection signal helps to assimilate the occultation data into the numerical weather prediction system, which has important significance. This paper proposes a deep learning model based on improved GoogLenet (Im-GNet) and applies it to COSMIC-2 occultation detection data to identify reflected signals. This article selects the COSMIC-2 occultation data (conPhs file) from January 1 to 9, 2020. After quality control, the radio holography method is used to obtain the spatial spectrum image of the occultation signal, and the Im-GNet deep learning model is trained , The accuracy rate of Im-GNet model test reached 96.4%, which is significantly higher than the result of support vector machine (SVM) method. This paper also analyzes the impact of reflected signals on occultation data. The geographic distribution of occultation events, and the refractivity comparison between the occultation inversion data (atmPrf file) and the NCEP (National Centers for Environmental Prediction) 12 hour forcast files (avnPrf file) shows that the quality of the occultation event data with reflection signals is better and the atmospheric information contained is richer.

      • WEN Qing, He Guorui, YANG Haijun

        Available online:March 17, 2022  DOI: 10.3878/j.issn.1006-9895.2101.21109

        Abstract:In this study the influence of Tibetan Plateau and Rocky mountain on ENSO variability is investigated using a fully coupled climate model. Compared to that in the real world, the amplitude of ENSO variability becomes larger after removing the Tibetan Plateau or Rocky mountain; The effect of Tibetan Plateau on ENSO is much more direct than that of Rocky mountain. The ENSO amplitude is much stronger in a world without the Tibetan Plateau than that without the Rocky mountain. The ENSO variability is closely linked with mean climate in the tropical Pacific. Removing the Tibetan Plateau results in weakened trade winds, an eastward shift of atmospheric convection center, a shallower mixed layer depth and an El Ni?o-like sea surface temperature (SST) distribution. These mean climate change cause enhanced wind-stress sensitivity, Ekman upwelling sensitivity and thermocline sensitivity, finally leading to a 60% increase of ENSO amplitude. However, in a world without the Rocky mountain, the tropical Pacific exhibits a more complicate trade wind change, with a slight eastward shift of atmospheric convection center, a deeper mixed layer depth, a flattened thermocline and a La Ni?a-like SST distribution. These mean climate responses strengthen the wind stress sensitivity and thermocline sensitivity, leading to a 10% increase of ENSO amplitude. This study suggests that the uplift of the Tibetan Plateau and Rocky mountain during the geological period have played a role in suppressing the ENSO variability, and the former plays a much more prominent role.

      • 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

      • CHEN Quanliang, GAO Guolu, LI Yang

        Available online:March 11, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21118

        Abstract:The material transport of deep convection in the upper troposphere-lower stratosphere (UTLS) has an important impact on the radiation balance of the tropopause, ozone restoration in the stratosphere, and global climate change. In recent years, a series of important observational facts have found that the Tibetan Plateau and the Asian monsoon regions are important windows for tropospheric to stratospheric transport (TST). This article introduces some of the major progress and achievements made in recent years, and it includes four points. Firstly, the maximum value area of water vapor and aerosol, the minimum value area of ozone were found by satellites over the Tibetan Plateau and the Asian monsoon region. Secondly, the main observation methods of deep convection activities and the identification method of satellite observations on deep convection. Thirdly, the physical process of deep convection materials transport to the stratosphere over the Tibetan Plateau. Fourthly, a comparison of the structural differences between deep convections in the Tibetan Plateau, Asian monsoon region, and tropical ocean regions, as well as the impact of differences in environmental fields on the process of deep convection material transport.

      • Zhang Jinru, Yang Lianmei, Liu Fan, Li Jiangang

        Available online:March 07, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21112

        Abstract:Based on Ka-band millimeter wave cloud radar and rainfall data from automatic weather stations, this study analyzed the physical characteristics of rainfall clouds in the West Tianshan Mountains, from May-August 2019 and 2020. The results show that: (1) Rainfall mainly occurs at night. The cumulative rainfall was concentrated from 21:00 to 07:00 the next day. There was a significant positive correlation between rainfall frequency and accumulated precipitation. The frequency of heavy rainfall was the least, but the contribution to the total accumulated rainfall was significant; (2) The maximum average reflectivity of light rainfall intensity, moderate rainfall intensity, and heavy rainfall intensity were 30 dBZ、35.8 dBZ, and 39.5 dBZ, and the maximum average liquid water content was 1.5 g·m-3、4.2 g·m-3、7.3 g·m-3;(3) There are two concentrated areas for the reflectivity of different rainfall intensities. The reflectivity of 2.0~4.4 km were concentrated in 15~26 dBZ, and the reflectivity of light rainfall intensity, moderate rainfall intensity and heavy rainfall intensity near the ground were respectively concentrated in 24 ~32 dBZ, 29~38 dBZ and 31~42 dBZ. The frequency of moderate rain intensity and heavy rain intensity below 1.75 km where the liquid water content is less than 1 g·m-3 is significantly less than that of light rain intensity. The greater the rainfall intensity, the more concentrated the radial velocity of rainfall particles.

      • CAO Xuejian, QI Youcun, LI Mengdi, YANG Zhida, NI Guangheng

        Available online:March 07, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21191

        Abstract:Traditional urban flood forecasting mostly adopts the mode of driving an urban hydrodynamic model with a single rainfall product, which is difficult to solve the uncertainty due to rainfall measurements or numerical modeling. Comprehensive utilization of multi-source precipitation (radar, rain gauge, and distrometer), and surface ponding observation will help improve both the forecasting accuracy of waterlogging and the spatial description of risk. Therefore, to better cope with the threat of extreme storms, this study proposes a warning system of urban waterlogging based on comprehensive observations to further strengthen the ability of flood forecasting, and has conducted preliminary practice and validation in the Qing River Basin of Beijing. The system contains six modules, integrates emerging observation technologies of both rainfall and waterlogging, introduces a mainstream method of rainfall nowcasting, and adopts well-established simulation methods of urban flooding. It can provide real-time water depth for road traffic and early warning products for urban emergency management.

      • 周玉淑

        Available online:March 01, 2022  DOI: 10.3878/j.issn.1006-9895.2109.21140

        Abstract:This article reviews and summarizes the research progress of atmospheric equation of vertical motion, as it plays a vital role in the occurrence and development of weather systems (especially of the small and medium-scale systems). Conservation of mass, the vertical motion can be calculated by the integration of continuity equation, but this algorithm requires accurate calculation of divergence, which is difficult to implement. The adiabatic method to calculate vertical motion is not accurate either because the based assumption of adiabatic internal changes in atmosphere does not agree to the thermal variations in real atmosphere. The diagnosis of vertical motion is related to the atmospheric scales, while the large-scale system is dominated by vortex motion and meets the quasi-horizontal motion, not to mention the little consideration of buoyancy as well as wind shear effect. For that reason, the vertical motion equation which takes account of the first law of thermodynamics, the atmospheric state equation, hydrostatic equilibrium and quasi-geostrophic condition is preferably applied in large-scale motion. The equation of vertical motion is more complicated in a meso-scale system due to the equally importance between the convergent or divergent motion as well as the rotational motion. Likewise, the vertical motion cannot be ignored. But the forcing term is still composed by the vorticity advection variation with height and the Laplace of temperature advection, thus it essentially has little distinction with the ω equation in a large-scale system. Convergent and divergent motion are predominant in a strong small-scale storm motion, with the buoyancy and wind shear playing the leading role, and the equation of vertical motion is much more complicated. However, the vertical motion forced by the background field still exists since none of the strong small-scale convective systems can occur in its isolation from the large or medium-scale background field. Thus the complete vertical motion should consider the vertical velocity generated by the adjustment of weather systems with different scales, namely, the combination of the vertical motion equations should be conducted for the calculation. The new equation of vertical motion with multiple effects can make the diagnostic analysis on the vertical velocity more precise in a strong convective system with small scale.

      • Gao Mingxiang, Yang Shuangyan, Wang Qiang, Li Tim

        Available online:February 28, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21105

        Abstract:Based on ERA-interim reanalysis daily data during 1979–2019, the impact of Madden-Julian Oscillation (MJO) on Pacific blocking frequency during two types of El Ni?o (Eastern and Central El Ni?o) is examined using a two-dimensional blocking index. Phase 3 and 7 with the higher frequency and the stronger amplitude are selected in this study. It is found that the locations of MJO teleconnections are similar in MJO phase 3 during the Eastern and Central El Ni?o years (EP3 and CP3), corresponding to a positive (negative) geopotential height anomaly in the polar region (the Bering Sea). Thus there are positive blocking frequency anomalies in the high-latitude Pacific sector during the EP3 and CP3. The blocking frequency anomalies over the mid-high-latitudinal Pacific are significantly positive in MJO Phase 7 during the Eastern El Ni?o years (EP7), but are not largely significant in MJO Phase 7 during the Central El Ni?o years (CP7). Because the subtropical westerly jet shifted to the north in the EP7, the MJO teleconnection locates in the north of 50°N. This teleconnection corresponds to the geopotential height anomalies, which increase the Pacific blocking frequency, in the Pacific sector. However, the subtropical westerly jet shifted to the south in the CP7. The teleconnection locates between 40°N and 50°N, resulting in weak influence to geopotential height in the Pacific region. So there are not largely significant blocking frequency anomalies over the Pacific region in the CP7. Finally, the ECHAM4.6 model is used to verify the above conclusions.

      • HAN WENJUN, YU YUEYUE, ZHOU YUMENG, CHEN SHENGJIE, GUAN ZHAOYONG, HUANG WEI, WU WENLU, LIAO LIANGMENG

        Available online:February 28, 2022  DOI: 10.3878/j.issn.1006-9895.2109.21065

        Abstract:The first snowstorm event occurred in Jiangsu during January 3-5, 2018 had larger snowfall but lower snow accumulation efficiency, while the following second snowstorm event during January 24-28 had smaller snowfall but higher snow efficiency. Using the ERA-Interim reanalysis data and the observation data from the China Meteorological Administration, this study investigated the temperature and humidity conditions in these two snowstorm events and explored the underlying physical processes in the framework of isentropic atmospheric mass circulation. Main results are as follows: (1) The early stage of the first snowstorm event was characterized by higher temperature in the entire troposphere, which was attributed to a relatively deeper and stronger poleward warm air branch of isentropic atmospheric mass circulation to the south of Jiangsu, compared to the second snowstorm event. In contrast, in the second snowstorm event, the stronger equatorward cold air branch of isentropic atmospheric mass circulation resulted in the temperature lower than 0℃, which promoted the higher snow accumulation efficiency. (2) The deep water vapor convergence layer in lower isentropic layers collaborated with the wide range of ascending motions during the first snowstorm, and further brought lower-level water vapor to higher layer for the formation of larger snowfall. Larger meridional water vapor transport but weak zonal water vapor divergence in the low isentropic layers caused the near-ground specific humidity to increase significantly and thus contributing to the lower snow accumulation efficiency. However, in the second snowstorm event, there was a deep layer of water vapor divergence in the lower isentropic layers, which contributed to the larger snow accumulation efficiency. Therefore, colder and dryer conditions resulting from the abnormal meridional cold air transport and weak water vapor transport in both meridional and zonal directions are the key factors for the higher snow efficiency in the second snowstorm event. The comparison of spatial distribution of temperature and humidity with that of the snow efficiency further shows that the snow efficiency is more sensitive to the local temperature and humidity under the condition of high temperature and humidity.

      • Lin Huijuan, Li Muyang, Zhuang Bingliang, Chen Huimin, Wei Wen, Gao Yiman, Wang Tijian, Li Shu, 陈璞珑

        Available online:February 28, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21163

        Abstract:Black carbon (BC) aerosol have important impacts on regional and global climate change. China and India are the world"s largest anthropogenic BC emitters. In this paper, the newest generation of regional climate model RegCM4 is used to investigate the direct impact of BC emissions from major areas of India and China on east Asian climate in winter. The results show that the total BC column burden, top of atmospheric and surface effective radiative forcing from east Asia are 1.784 mg/m2, +1.982 W/m2 and -2.170 W/m2, respectively. The influence of BC in China and India on regional climate is different. The Indian BC will cause the regional 850 hPa and surface cooling, while the Chinese BC will cause the regional 850 hPa warming and surface cooling. In addition, BC inChina has a stronger climate response in East Asia due to its higher emissions and wider distribution, and plays a leading role in regulating the regional climate in East Asia. In general, BC in both places will cause cloud cover to decrease by 0.21% near 850hPa, air temperature to increase by 0.014 K near 850hPa, sunshine duration to decrease by 0.135 h/day, surface air temperature to decrease by about 0.091 K, sensible heat flux to decrease by 1.161 W/m2. Surface evaporation decreased by 0.027 mm/day, boundary layer height decreased by 7.072 m, POA column burden decreased by 0.027 mg/m2, sulfate aerosol column burden increased by 0.035mg/m2. The results further suggest that the direct response of east Asian winter climate to different BC emissions is nonlinear.

      • WUKE, CHENHUIMIN, WANGTING, ZHUANGBINGLIANG, WANGTIJIAN, XIAYUNYU, WUJUNMEI

        Available online:February 28, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21171

        Abstract:In order to deal with the COVID-19 outbreak, Kunshan has strictly followed the national epidemic prevention regulations and has taken strict lockdown measures since January 24, 2020. Anthropogenic emissions, led by motor vehicle activity, have been reduced and air quality has changed as a result. Based on the environmental monitoring network, combined with the meteorological observation system, the integrated use of mathematical statistics and spatial analysis methods have been applied to investigate the impact of variations in human activity patterns on the air quality of Kunshan city before (from January 1, 2020 - January 20) and during the lockdown (from January 27, 2020 - February 15). The results show that great progress has been made in pollution control comparing with the same period (from January 1 to February 15) in the past three years, in that the days of exceeding the standard of particulate matter (PM2.5 and PM10) have decreased by 4 days. The daily maximum 8-hour ozone concentration (MDA8 O3), however, has increased by 14%, indicating that severe O3 pollution is about to be a problem throughout whole year rather than limited in summertime. Due to the reduction of emissions mainly from transportation sector during the lockdown, the concentration of nitrogen dioxide (NO2), an important precursor of O3, and particulate matter decreased significantly while MDA8 O3 increased during this period (62%). It is found that severe pollution events may occur even in the case of emission reduction, so the influence of meteorological conditions on air quality cannot be ignored. It is found that serious pollution events may occur even in the case of emission reduction, so the influence of meteorological conditions on air quality cannot be ignored. This study further improves the insights into the characteristics of main pollutants in Kunshan in winter, and explores the impact of anthropogenic emissions and meteorological factors on pollutants, which will provide a scientific reference for the simulation and prediction of aerosol at the urban scale in the Yangtze River Delta, China.

      • Tan Hui, Zhu Zhiwei

        Available online:February 24, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21117

        Abstract:Based on the daily cloud cover derived from the 1078-gauge stations in eastern China during 1961-2003, the temporal-spatial characteristics of the leading mode of winter cloudy day frequency (CDF) over eastern China are revealed via Empirical Orthogonal Function analysis. We revealed the two influence routes of this leading mode, based on which the physical-motivated empirical model is conducted to the seasonal prediction of the winter CDF in eastern China. The results show that: (1) the first EOF mode of winter CDF explains the 59% of the total variance, which is significant and independent from the other modes. This mode mainly shows a homogenous spatial pattern over eastern China and presents a dominant interannual variability. In the positive phase of this mode, a significant lower-level anticyclonic circulation anomaly appears over North Pacific. The anomalous southerly wind over the western flank of the anticyclonic could transport water vapor from tropical ocean to eastern China, leading to increased CDF; (2) the preceding persistent North Pacific subtropical SSTA dipole pattern (NPD) during August and September, and lowing of sea level pressure over midlatitude North Atlantic (LPA) from September to November are the two independent drivers for the formation and variation of this mode. The cold SSTA in the western pole of the NPD is advected southward to the tropical western Pacific by the anomalous northerly of the local low-level anomalous cyclone, and the Bjerknes feedback is then formed which further maintains and accelerates “west cold east warm” zonal SSTA dipole pattern in tropical Pacific. This tropical Pacific zonal SSTA pattern stimulates zonal convection dipole, which further induces a meridional atmospheric teleconnection in the North Pacific. The southerly over the west of the anomalous North Pacific anticyclone is conducive to more CDF in eastern China. The LPA reflects the transition of quasi-stationary Rossby wave train in mid-high latitudes Eurasia from autumn to winter. In winter, the southerly on the west of the barotropic anticyclonic anomaly over the Northeast Asia, the terminal of the Rossby wave train, could also results in more CDF in eastern China; (3) Based on these two independent routes of physical mechanisms from both tropics and ex-tropics, a physics-motivated empirical model is conducted, which shows encouraging independent prediction skill during the ten years of 2004-2013. The results therein are useful references for operational departments on seasonal prediction.

      • Cheng Zelun, Xie Zuowei

        Available online:February 24, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21120

        Abstract:Global warming has increased the intensity and frequency of extreme precipitation events. Indochina Peninsula and South China (INCSC) is located in the monsoon region and thus is vulnerable to extreme precipitation with flood disaster. Using daily precipitation data, this paper objectively classified the extreme precipitation events in the INCSC region during the wet season (May to October) over 1951 to 2015. The circulation characteristics and interannual, interdecadal and long-term trend characteristics of each extreme precipitation cluster were analyzed. The results suggest that (1) According to the location of precipitation center, the extreme precipitation in the INCSC region can be objectively grouped into South China, Indochina Peninsula, Burma–Yunnan, and Southern South China–Northern Vietnam clusters. The associated large-scale meteorological patterns (LMP) are characterized by mid-high latitude wave trains and tropical dipole circulation. The LMP of the South China cluster features a "+ ? +" meridional wave train in the upper troposphere, which bears some resemblance with the East-Asia Pacific (EAP) teleconnection pattern. However, the centers of LMP lie southwestward to the EAP counterparts. The negative anomaly circulation in central East China is the key system. In the lower troposphere, LMP features a "+ ?" meridional wave train located at low latitudes. The LMP of the Indochina Peninsula cluster features a dipole anomaly circulation of enhanced monsoon trough and Mascarene high pressure in the upper to lower troposphere. The LMPs of the other two clusters of extreme precipitation have a combination of Rossby wave train in the upper troposphere and the moderate tropocial diople in the lower troposphere. (2) The occurrence of extreme precipitation days in the INCSC region exhibits a significant upward trend, which is contributed by the South China and Indochina Peninsula clusters. The occurrence frequence of meridional wave-train LMP increased the extreme precipitation days in the South China cluster. (3) The extreme precipitation of Indochina Peninsula and South China clusters are antisymmetric with each other. From the perspective of the Indochina Peninsula cluster, the maintenance of low pressure elongating from the Arabian Sea via Indochina Peninsula to South China Sea is unfavorable for the occurrence of extreme precipitation in South China.

      • Liang Jing, Sun Jianqi

        Available online:February 24, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21172

        Abstract:The relationship between spring sea surface temperature in the North Atlantic and extreme cold event (ECE) frequency in eastern China at interannual timescale is investigated in this paper. The results show that the North Atlantic tripolar SST mode (NATSST) can significantly affect the first leading mode of ECE frequency in eastern China after the late 1980s, but not before. Further mechanistic analysis suggests that such an interdecadal change in the relationship between the two could be related to the difference in the NATSST-excited wave trains before and after the late 1980s. In 1960-1987, the NATSST-related wave train propagates from the North Atlantic to southern Central Asia, which is located more southward and consequently has a weak influence on atmospheric circulations and ECE in eastern China. However, in 1992-2019, NATSST can excite two wave trains. The northern one is associated with the North Atlantic Oscillation (NAO), which propagates eastward from the North Atlantic to mid-high latitudes of Eurasia, resulting in anomalous cyclonic/anticyclonic circulation in the Mongolian region. The southern one propagates eastward from the North Atlantic to mid-low latitudes of Eurasia, leading to anomalous cyclonic/anticyclonic circulation in southern-central China. These cyclonic/anticyclonic circulations are favorable/unfavorable to the southward movement of cold air from middle and high latitudes, and also change the surface heat flux in eastern China, consequently providing favorable/unfavorable climate background conditions for the occurrence of ECE. Through these physical processes, NATSST can significantly influence the interannual variability of the frequency of spring ECE in eastern China after the late 1980s, but not before.

      • ZHENG Ran, CHEN Lijuan, LI Weijing, Wang Shunjiu, MA Zhenfeng, LIANG Ning, LIU Jiahuimin

        Available online:February 24, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21167

        Abstract:Based on the precipitation observation data of 134 stations in Sichuan Basin, the ERA-Interim reanalysis datasets, sea surface temperature (SST) and sea ice datasets from the Met Office Hadley Centre, this study investigates two major modes of summer precipitation over Sichuan Basin through empirical orthogonal function (EOF) method and linear regression technique. It is found that EOF1 shows the consistent pattern in whole region, and EOF2 reflects an inverse pattern between the east and west of Sichuan Basin. The dominant mode is the east-west reversed pattern in the 1980s and the consistent pattern from the 1990s to the beginning of the 21st century. In recent years, the inverse pattern restore to the dominant position. Further research shows that the EOF1 of precipitation is significantly affected by the low-latitude circulation in 500hPa geo-potential height, especially by the western Pacific subtropical high (WPSH). The 850hPa wind over the basin is controlled by convergent or divergent fields. It is jointly affected by the Bay of Bengal, South China Sea, and Western Pacific water vapor channels. The South China Sea vapor channel may play the key role. The more or less precipitation of EOF1 is corresponding with the consistent input or output of water vapor at the North-South boundary of the basin. The pre-signal for most cases in EOF1 may come from the decaying phase of the El Nino-Southern Oscillation (ENSO). However, the EOF2 is greatly related to the mid and high latitude circulation in 500hPa, which similar to the Polar/Eurasia (POL) pattern. The EOF2 mode with more in the west and less in the east of Basin is connected with the input of the south border and the output of the north border, and vice versa. The EOF2 pattern has a significant relationship with the water vapor channel in the western Pacific. The pre-signal for most cases in EOF2 may originate from the variability of Arctic sea ice.

      • wangjun, 姚展予

        Available online:February 23, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21104

        Abstract:Based on data of THIES disdrometer and CINRADA/SA Doppler radar, the raindrop size distribution and integral parameters of convective precipitation in two mesoscale system,whose maximum rain intensity were 483.0 and 418.9mmh-1 respectively, were analyzed. The results shows that:The two precipitation processes wereboth affected by the southwest airflowoutside the subtropical high and the westerly trough withthe characteristics of high temperature and high humidity, which were conducive to the production of heavy rain. On August 3, 2015, the echodeveloped more strongly and was in the mature and weakened stage near the observation point.On July 26, 2017,two linear mesoscale convective echoeswere merged near the observation point, and the echo was in the stage of development and enhancement.In severe convective precipitation episode (rain intensity R>20 mmh-1), for the raindrop concentration (NT), the exponential function can be used to fit theNT with the increase of R. On August 3, there was a large coefficient and a small index, while on July 26, it was just the opposite. For the the median volume diameter of the raindrop, on August 3, D0 rapidly increased with the increase of R, and the slope of the fitting line was large, whilelgNw gradually decreased with the increase of R. On July 26, D0 and lgNware both positively correlated with R, but D0 increased slowly with the increase of R, and the slope of the fitting line was small. For the Z-R relationship, the precipitation on August 3 had a smaller coefficient and a larger index, while the precipitation on July 26 had a larger coefficient and a smaller index. For the characteristics of mean raindrop size distribution of convective precipitation at different rainfall intensities, On August 3, when the rain intensity was more than 100 mmh-1, the particle number density of large raindrops with a diameter of 3-6 mm increased significantly with the increase of the rain intensity. On July 26, the number density of raindrops in each diameter range increased with the increase of rainfall intensity. In conclusion, based on the relationship between integral parameters and rain intensity and the average raindrop size distribution, the precipitation on August 3 was the typical size controlled raindrop size distribution characteristics, while the convective precipitation on July 26 was the concentration-diameter mixed controlled raindrop size distribution characteristics.The NW-D0 distribution of the normalized Gamma function showed that the convective precipitation of the two cases had the characteristics of typical rain drop size distribution of continental convective precipitation. Many raindrop size distribution in the processes of August 3 showed the characteristics of ice phase and warm rain mixed convective precipitation, but most of the convective precipitation in the two processes had the rain drop size distribution characteristics of ice-based.

      • SHU Weixi, FAN Shuiyong, HUANG Ying, REN Jing, SHEN Shujing

        Available online:February 23, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21204

        Abstract:Based on the raindrop spectrum observation data of Urumqi, Xinjiang from July 3 to October 3, 2018, this paper improved the WRF Single-Moment 6-class (WSM6) scheme in Urumqi regional high-resolution numerical prediction system, and evaluated the improvement effect of a heavy precipitation process prediction in Xinjiang from 1200 BJT on June 15 to 0000 BJT on June 17, 2021. The results show that the average diameter (D0), maximum diameter (Dmax), and mass weighted average diameter (Dm) of raindrops in Urumqi were 0.65 mm, 1.60 mm, and 0.93 mm, respectively based on the raindrop spectrum observation. The WSM6-new scheme considering the fitting relationship between parameters lgNw and Dm in Xinjiang improved the prediction ability of the intensity and strong center range of precipitation to a certain extent. The scoring results of TS, BR, ETS, and TSS show that with the increase of precipitation grade, the prediction ability of WSM6-new scheme was significantly improved, and it showed obvious advantages for the prediction of heavy rain and torrential rain. The parameter scheme with different raindrop size distribution had a certain impact on the structural characteristics of precipitation cloud system, vertical velocity, atmospheric stratification, and divergence field. The impact on cloud microphysical processes was mainly reflected in the content and distribution of rainwater. WSM6-new scheme adopted the statistical characteristics of raindrop spectrum in Xinjiang, which made the description of raindrop size distribution in the model closer to reality. The number concentration of large raindrops in raindrop spectrum increased obviously, the terminal velocity of raindrops increased, and the drag effect enhanced, which was conducive to the enhancement and maintenance of downdraft below frozen level. The strong downdraft formed a strong divergent outflow in the near ground layer, which strengthened the air convergence in the convection area near the ground and was of benefit to the development and strengthening of the updraft. Therefore, a stronger precipitation process appeared on the ground, and the prediction ability for heavy rain and torrential rain was obviously enhanced.

      • 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.

      • Zhou Jiean, Tao Li, Xie Zihuang

        Available online:February 23, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21207

        Abstract:Based on the causality of information flow, sea surface temperature (SST) and air-sea indexes are used to select factors which can affect the interannual variation of the dominant modes of accumulated cyclone energy (ACE) in the western North Pacific (WNP) from July to August. Then, the multiple linear stepwise regression method is used to select the most significant predictors. The first two modes of July-August ACE are the basin mode and dipole mode obtained by empirical orthogonal function (EOF) analysis. The prediction factors of principal component (PC) of basin mode include 3-month leading SST in Marine Continent and central North Pacific, 5-month leading quasi-biennial oscillation index (QBO),and 11-month leading tropical Indian Ocean dipole mode index (TIOD); while the prediction factors of PC of dipole mode include 2-month leading SST in North Atlantic, 12-month leading SST in Japanese trench, 7-month leading Atlantic meridional mode index (AMM) and 8-month leading North Atlantic Oscillation index (NAO). The prediction equations are established based on these prediction factors. The correlation coefficients between the predicted PCs and the observed PCs of the first two modes reach 0.75 and 0.77 respectively, which both are statistically significant at the level of α=0.01. The cross-validation method indicates the prediction equations have good hindcast skills and stability. The temporal correlation coefficient skill of WNP area averaged ACE anomaly reaches 0.76. The averaged pattern correlation coefficient skill of ACE anomaly reaches 0.35 over the WNP basin during 1980-2020. The prediction model performs pretty well in the years when the ACE can be reconstructed by the first two modes.

      • chen boyu

        Available online:February 23, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21186

        Abstract:Based on multi-source observations, reanalysis and convection-resolving model forecast data, the characteristics and formation mechanism of the sudden rainstorm process in Mianning of Sichuan province on June 26, 2020 were analyzed by using physical quantity diagnosis, standardized anomaly analysis, comparison with similar processes. Results were as follows: (1) The process was a local sudden rainstorm process with several banded meso-γ convective systems and extreme hourly precipitation,which generated by the "train effect" . The center of convective echoes was low, and the convective cloud clusters had the characteristics of mesoscale convective complex. (2) The surface convergence and uplift, formed by the outflow of convective cold pool in the northern part of Mianning and the strong southerly wind in valley, constituted to the convection triggering. (3) The southerly low-level flow in Southwest Sichuan had the characteristics of phased enhancement, and provided continuous warm and moist air transportation. Its interaction with the downhill cold pool in the early stage of the process and confluence with the southward cold air from western basin at the later stage of process, caused convective cells were repeatedly triggered on the west and south side of Mianning station, and generated the "train effect" in downstream areas. (4) Compared with similar process in history, the physical quantities such as convective effective potential energy of environmental atmosphere had more significant anomalies and persistence of anomalies. (5) The high-altitude terrain in the northern part of Southwest Sichuan has a significant effect on delaying the entry of cold air into Anning river valley and maintaining unstable stratification in the valley. The forcing uplift of the terrain in this area formed a potential convection triggering condition in upstream areas of the river valley. Finally, the conceptual model of the formation mechanism of this rainstorm process was presented.

      • Sun Wanyi, Zhu Congwen

        Available online:January 27, 2022  DOI: 10.3878/j.issn.1006-9895.2111.21184

        Abstract:Owing to the complicated change of East Asian summer monsoon and chaotic influence, the accurate forecast of summer rainfall anomalies in North China is a great challenge. To understand the origin of summer rainfall anomalies in this region, we applied the daily observed rainfall with CRA-40 atmospheric reanalysis, harmonic and MV-EOF analysis to examine the impact of annual cycle of East Asian subtropical summer monsoon (EASSM) on the summer rainfall anomalies in North China during 1979-2020. Our results show that, in climatology, the rainfall related seasonal cycle of winds at 850hPa in North China exhibits two dominant modes, characterized by the southwestly and southeastly, which reaches their peak in early and late July, respectively. Although the rainfall in North China revealed by the first two modes exhibits consistent changes on interannual scale, it is successively affected by southwestly wind and southeastly wind anomalies. Based on the analysis of the onset date (P1), peak date (P2), retreat date (P3), duration (D) and amplitude (A) of the annual cycle modes during the rainy season and the summer monsoon rainfall (from June to August) anomalies in North China, We found that the onset and retreat date, and the amplitude of annual cycle modes dominated by southeast wind are significantly positively correlated with the summer rainfall anomalies in North China, while the peak date and duration are negatively correlated with the summer rainfall anomalies in North China. Its phases (P1, P2, P3) variation are related to the intensity of southwest wind in summer, while the amplitude (A) variation mainly depends on the intensity of southeast wind. The peak date, retreat date and amplitude of the second annual cycle mode, dominated by southwestly wind shows a significantly positive correlations with summer rainfall anomaly in North China. Since the summer rainfall dominated by the southeast wind starts from April to May, the establishment of the EASSM related to the rainfall in North China provides a new index for the seasonal forecast of summer rainfall in North China.

      • LIU JING, Liu Zhaoxu

        Available online:January 25, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21095

        Abstract:In this study, multiple data sources were used to conduct an in-depth analysis of two extreme rainfall events that occurred in the south-eastern Hami area in 31 July 2018 (hereinafter referred to as ‘7.31’ process) and in the northern Hami area (Xinjiang, China) in 8 August 2016(hereinafter referred to as ‘8.8’ process). Based on calculation of the frontogenesis function using 0.25° x 0.25° NCEP/NCAR FNL reanalysis, the difference of mesoscale convection trigger factors were compared and analyzed during two heavy rainfall events. The results showed:(1)During ‘7.31’ heavy rainfall, the 500 hPa western Pacific subtropical high was anomalously northerly, and was westerly during “8.8” heavy rainfall; several mesoscale cloud clusters generated in front of the 700 hPa Hexi corridor jet stream in “7.31” heavy rainfall, and generated in front of the 700 hPa southwesterly jet stream in “8.8” heavy rainfall. (2)In “7.31” heavy rainfall, the atmosphere was conditionally unstable over the region and unstable convective energy was triggered by warm frontogenesis at the low troposphere. Warm frontal frontogenesis was determined by the horizontal divergence and the tilt term during convective initiation, and deformation and tilt terms as convection at matured.(3)During ‘8.8’ heavy rainfall period, the convective cloud clusters was triggered by cold frontogenesis at the low troposphere, and then merged and developed along the 500 hPa steering flow. The atmosphere was conditionally unstable over the region and unstable convective energy. Warm frontal frontogenesis was determined by the horizontal divergence and the tilt term during convective initiation, and deformation and tilt terms as convection at matured. Additionally, the maintenance and intensification of the 700 hPa shear line was favor to cold frontal frontogenesis. It was also the main responsibility for the long life period of mesoscale convective system. Cold frontal frontogenesis was determined by the horizontal divergence term as convective initiation, and tilt terms as convection at matured.

      • Zhang Xiaolu, Jiang Dabang

        Available online:January 20, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21182

        Abstract:In this study, we project the changes in temperature and precipitation over Xinjiang during 2015~2099 relative to 1995~2014 by using 20 global climate models, which have good performance in simulating climatological temperature and precipitation over this region, from Coupled Model Intercomparison Project Phase 6 (CMIP6) under the three Shared Socioeconomic Pathways (SSPs). Multi-model median results indicate that annual and seasonal temperatures will increase during the 21st century, with larger values in the basins than in the mountains. The trends of annual temperature changes under SSP1-2.6, SSP2-4.5, and SSP5-8.5 are 0.1 ℃/10a, 0.3 ℃/10a, and 0.7 ℃/10a, respectively. The regionally averaged temperature will increase by 1.3 ℃, 2.6 ℃, and 5.3 ℃ during 2080~2099, with the strongest warming occurring in summer. The regionally averaged consistency in sign of projected annual and seasonal temperature changes is larger than 90%, and the inter-model uncertainty will increase with time, with larger values under SSP5-8.5 than those under SSP1-2.6 and SSP2-4.5. Larger uncertainties occur in the projection of seasonal temperatures than that of annual case, except for spring. Precipitation is expected to increase over Xinjiang during the 21st century. The maximum increase of more than 50% locates in the central Tarim Basin under the SSP5-8.5 scenario during 2080~2099. Under the SSP1-2.6, SSP2-4.5, and SSP5-8.5, the trends of annual precipitation changes from 2015 to 2099 are 0.2%/10a, 2%/10a, and 4%/10a, respectively, and annual precipitation increases by a regional average of 5%, 13%, and 25% during 2080~2099. The largest increase in precipitation occurs in winter. The inter-model consistency in sign of projected annual and seasonal precipitation changes increases with time but is weaker than its temperature counterparts. The inter-model uncertainty for precipitation projections will increase with time, with the largest magnitude under SSP5-8.5. The inter-model uncertainty of seasonal precipitation projections are larger than that of the annual case.

      • ZHANG Danyuting, LIAO Hong, LI Ke, DIA Huibin

        Available online:January 20, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21218

        Abstract:The GEOS-Chem model was applied to examine the effects of changes in anthropogenic emissions and meteorological parameters on the changes in summertime OH concentrations in China since the implementation of the Air Pollution Prevention and Control Action Plan. Our modeling results over years of 2014–2017 show that summertime OH concentrations in China exhibited an overall upward trend with the fastest increases around the 30°N over eastern China; the North China Plain was also simulated having an obvious upward trend of OH concentration of 0.1×106 molec cm?3/year, while the Pearl River Delta experienced a weak trend. Further sensitivity experiments simulations showed that changes in both meteorology and anthropogenic emissions over 2014–2017 contributed to the increases in OH concentrations in the North China Plain, in which the contribution of anthropogenic emissions was significantly larger than that of meteorology (10% vs. 1.5%); Meteorology played a dominated role in OH increase around 30°N over eastern China. Our further meteorological analysis shows that the meteorological variable with the greatest contribution was solar shortwave radiation, which can explain the OH changes over a large fraction of China during 2014–2017. However, the role of solar shortwave radiation was offset by the boundary layer height in affecting 2014–2017 OH changes in the North China Plain.

      • wang shuang, wu qigang, liu shizuo, liang hanzhou, 户元涛, kang caiyan, bao xiaojun, gao yan

        Available online:January 19, 2022  DOI: 10.3878/j.issn.1006-9895.2111.21051

        Abstract:The primary mode of empirical orthogonal decomposition (EOF) of Antarctic sea ice is a dipole anomaly, with the positive and negative anomaly centers over the Bellingshausen Sea/Amundsen Sea and the Weddell Sea, respectively, which is known as the Antarctic sea ice oscillation or Antarctic Dipole. Previous studies have shown that the Antarctic sea ice oscillation in austral winter and spring have a significant effect on the later Antarctic Oscillation (AAO) -type atmospheric circulation. This empirical study further examines the remote effects of the May-July (MJJ) Antarctic sea ice oscillation on boreal summer atmospheric circulation in the Northern Hemisphere and the associated physical processes. Results show that the Antarctic sea ice’s dipole anomaly has good persistence around austral winter from MJJ-JAS, which is conducive to triggering persistent AAO-like atmosphere responses in the troposphere and lower stratosphere, with the deepening of the low pressure zone around the polar region and the strengthening of the subtropical high pressure zone, and the increasing of the pressure gradient between the middle and high latitudes. Moreover, the latitudinal mean zonal wind presents a significant distribution of meridional teleconnection from the South Pole to the North Pole. In the middle troposphere, 700 mb geopotential height field displays significant negative anomalies from northern Australia to the maritime continent, and a significant positive anomaly center near Japan and a band-shaped negative anomaly appears near the Sea of Okhotsk and Aleutian Islands when the atmosphere lags behind the sea ice anomaly by zero to two months. It is another form of meridional teleconnection except for zonal wind. In addition, the negative geopotential height anomaly from the subtropical North America to the western Atlantic and the positive geopotential height anomaly center over the North Atlantic constitute a structure similar to the western Atlantic teleconnection (WA). In terms of the physical mechanism, Antarctic sea ice first affects the Ferrel circulation through local forcing effects. In turn, the ascending branch of Hadley circulation over the oceanic continental region and Tropical Atlantic are enhanced by the meridional circulation adjustment. Then the negative phase of Pacific Japan (PJ) wave train and WA teleconnection excited by the enhanced tropical convection affects the atmospheric circulation in the northern hemisphere. The strong tropical convection activity in the oceanic continental region (especially near the Philippines) and Tropical Atlantic, serves as a bridge to transmit the forced tropical signals to boreal summer East Asia-North Pacific, North Atlantic-Europe and other middle and high latitude regions in the northern hemisphere.

      • maxiaoyi, Fan Ke

        Available online:January 18, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21115

        Abstract:Based on the observation and reanalysis data during 1961–2014, the spatial and temporal features of the dry and wet changes in summer and autumn in Northwest China (35°-50°N, 75°-95°E) are investigated. We examine the contribution of evapotranspiration and precipitation to the linear trend of dryness and wetness. Meanwhile, the large-scale atmospheric circulations and water vapor budget related to interdecadal characteristics of dryness and wetness are analyzed. Results show that the drought variability in summer and autumn in Northwest China is the largest in the four seasons, and these two seasons are the highest probability of drought. However, there was a significant increasing trend of wetness in Northwest China from 1961 to 2014, in which evapotranspiration and precipitation play a significant role in the upwards trend in humidity over Northwest China. The increase in precipitation and the decrease in evapotranspiration both positively contribute to the trend of wetness in Northwest China. The total contribution rate of the two trends is 93.4% in summer and 67.5% in autumn. The interdecadal shift from dry to wet happened in summer and autumn around 1987 over Northwest China. Since 1987, the interdecadal humidification was mainly affected by changes in evapotranspiration and precipitation over Northwest China in summer. The decrease in evapotranspiration has a positive contribution to the humidification of the area, which is caused by the decrease in surface wind speed. The anomalous convergence of water vapor transport flux has led to an increase in precipitation in Northwest China. The water vapor diagnostic analysis further shows that the increase in precipitation mainly comes from the enhancement of local evaporation, with a contribution rate of 80%, indicating that local evaporation is an essential source of water vapor for precipitation. In addition, the summer water vapor advection term is positive (that is, water vapor flux convergence is strengthened), which has a positive contribution to the increase in precipitation. This contribution is mainly caused by the dynamic component related to wind speed. In comparison, the decrease in net radiation flux and surface wind speed simultaneously led to a decrease in evapotranspiration in Northwest China in autumn after 1987, which caused interdecadal humidification in the region.

      • zou wei, shen han, yuan hui ling

        Available online:January 18, 2022  DOI: 10.3878/j.issn.1006-9895.2105.20191

        Abstract:Radar data assimilation can improve the forecasts of severe convective weather, but different model configurations will generate different results. This paper studies a squall line process occurred in southern China on March 4, 2018. The Advanced Regional Prediction System (ARPS) Three-Dimensional Variational data assimilation system (3DVAR) is applied to assimilate Doppler radar radial velocity, and cloud analysis included in the ARPS model is used to process radar reflectivity data. Considering the assimilation interval, frequency and different parameter adjustments in cloud analysis, different assimilation schemes are designed by adopting the 1h assimilation window. Using the Global Forecast System (GFS) analysis data as the background field, the weather research and forecasting (WRF) model is used to investigate the influence of radar data assimilation on the triggering and development mechanism of the squall line system. The results show that when the assimilation interval is too short, false echoes are generated due to the imbalance of the model thermodynamic variables. When the assimilation interval is too long, the characteristics of the system triggering and development are generally weak. The best initial field is achieved by the 12min interval assimilation, and the higher the assimilation frequency, the better the precipitation forecast results. In addition, the ARPS cloud analysis can greatly improve the initial field and reduce the model spin-up time. Among them, humidity adjustment, temperature adjustment, rainwater adjustment, and water vapor adjustment have greater impacts on the dynamic process of the system and the initial field distribution of the hydrometeors in the initial field, while the adjustment of parameters related to vertical velocity has less impacts.

      • Su Haifeng, Dai Xingang, Xiong Zhe, Yan Xiaodong

        Available online:January 18, 2022  DOI: 10.3878/j.issn.1006-9895.2201.21081

        Abstract:This paper focuses on the dynamic and statistic-dynamic downscaling techniques for estimating the precipitation at the stations in Heihe river basin of Northwest China depending on local observations at 14 sites and the outputs from a regional climate model (RIEMS2.0) with a resolution of 3 km×3km grids. The precipitation estimated further respectively by a multiple regression (MLR) and a Bayesian Model Average(BMA) with different factor combination is tested on the assessment indices as the errors, variance, "negative precipitation bias" and correlation coefficient with observation. Results show that the precipitation produced by the dynamic model is of the biggest errors, the most significant coherence, much large variance than observation by factor of 2 about, while big errors, low correlation coefficient and lower variance than observation are estimated by the statistically downscaling model with the factors as geopotential height, v-wind and specific humidity on 700hPa. When the model precipitation is introduced into the statistically downscaling models, the indices become improved, in which the correlation and variance percentage of MLR"s models are much more higher than BMA"s, so do the errors and "negative precipitation bias". The negative precipitation produced by the statistically downscaling models appears manly in cold season or in dry- and extremely dry land such as lower reaches of the river, of which the negative precipitation frequency become decreased if the model precipitation is added as a factor in the downscaling models. Besides, the statistical assessment of the monthly precipitation estimated from the downscaling models reveals that the four indices would be evolving with season, in which the errors of the dynamical downscaling is also the biggest among the downscaling models, and their relative errors are smaller in summer and bigger in cold season, especially in lower reaches of the river. It implies that the precipitation downscaling in dry land or dry season is still a difficult task to be studied further. These results show that a significant bias exists in the dynamic downscaling even for the regional climate model with high resolution. So, the statistic downscaling has to be combined with the regional model for decreasing the uncertainties of the precipitation estimated in the river basin.

      • LIU JINGRU, LI YING

        Available online:January 14, 2022  DOI: 10.3878/j.issn.1006-9895.2110.21136

        Abstract:Using important weather reports from Chinese surface-based observing stations,the China Meteorological Administration (CMA) tropical cyclone best track data and hour-by-hour precipitation data from 2010 to 2016, statistical analysis of surface gales and its accompanying weather in southeastern China under the influence of tropical cyclones (TCs) was conducted, and the results show that: 1) TC gale in this region is mainly distributed along the coastline, with decreasing frequency from coast to inland; TC gale is dominated by the northeast wind direction, and the gale is mostly before the typhoon landfall. The strong wind speed of magnitude 12 and above are distributed within 300km of the TC center; 2) TCs of TS and TY intensity caused the most gale, but the strong wind speed of magnitude 16 and above are mainly found in the STY and Super TY intensity classes. Gale caused by slow TC mainly appears its shift to the right front side, and fast mainly appears its right rear side. The mean onshore wind speed of TC gale are slightly larger than the offshore wind speed, although the station frequency of onshore wind is more than that of offshore wind when the wind speed between level 12 and level 16,when the wind speed above level 16,offshore wind is much more than that of onshore wind ; 3) TC gale accompanied by precipitation accounts for about 89.8% of the total number of TC gale, distributed near the center of TC, with predominantly northeasterly winds and peak frequency occurring in August.TC gale without precipitation accounts for about 10.2%, mainly distributed in the periphery of the TC, with northerly and southeasterly winds predominantly with weak wind speed, mostly in May and December.TC gales with wind speed above level 12 are almost always accompanied by precipitation, while there are few samples of TC gales with wind speed above 12 without precipitation; 4) Accompanied by strong convective weather TC gale accounts for about 23.8% of the total TC gale, with northeasterly winds dominating, the average wind speed is greater than the non-strong convective TC gale; Strong convective weather including short-term heavy precipitation and thunderstorms, with the majority of short-term heavy precipitation (about 79.5% of this type of TC gale), mainly distributed in the northeast quadrant near the TC center, while thunderstorm TC gale mainly appears in the periphery of TC (about 28.0% of this type of TC gale), of which there are relatively few in the southeast quadrant. 5) TC gale with both short-time heavy precipitation and thunderstorms accounts for only 1.8% of the total TC gale and 7.5% of strong convective TC gale, indicating that thunderstorms were not common in TC gale with short-time heavy precipitation.

      • 宗海锋, Bueh Cholaw, LIN Dawei

        Available online:January 06, 2022  DOI: 10.3878/j.issn.1006-9895.2108.21052

        Abstract:Abstract Combined disaster event refers to the combination of several weather disasters that occur at the same time, and its occurrence will obviously aggravate the disaster. Using daily mean temperature, precipitation and glaze data of 206 stations over southern China in winter during the period from 1961 to 2013, an objective identification method is established for combined disaster events of extensive and persistent low temperature, rain/snow and freezing weather in winter, and the key features of these three kinds of combined disaster events are discussed. First, identification methods for extensive and persistent low temperature, rain/snow and freezing events are proposed, respectively, based on thresholds of their intensities and impact areas. On this basis, three most noteworthy combined disaster events, namely cold-rain/snow disaster event (C-RS), cold-freezing disaster event (C-F) and cold-rain/snow-freezing disaster event (C-RS-F) are identified. The three kinds of combined disaster events often occur during the period from early January to mid-February. Although the three kinds of combined disaster events have similarities in low temperature and precipitation, their formation conditions are obviously different. Abundant water vapor supply and large-scale strong water vapor convergence are key conditions for the occurrence of cold-rain/snow disaster event and cold-rain/snow-freezing disaster event, while inversion layer and cold pad are necessary conditions for the occurrence of cold-freezing disaster event and cold-rain/snow-freezing disaster event. The large-scale tilted ridge in the mid- and high latitude Asia is the key circulation feature of cold-freezing disaster event and cold-rain/snow-freezing disaster event, which provides favorable circulation conditions for strong cold air activities. During the cold-rain/snow disaster event, wavy circulation prevails in mid- and high latitude Asia, which is conducive to moderate cold air activities. In terms of water vapor supply and formation of inversion layer, the three kinds of combined disaster events are controlled by different subtropical anomalous circulation systems. The southern branch trough over the Bay of Bengal and the anomalous anticyclone over the South China Sea are key subtropical circulation systems for the formation of cold-rain/snow disaster event and cold-freezing disaster event respectively, while the combination of the southern branch trough over the Bay of Bengal and anomalous anticyclone over Northwestern Pacific is the key circulation system for the formation of cold-rain/snow-freezing disaster event.

      • majiao, weike, chenwe

        Available online:January 06, 2022  DOI: 10.3878/j.issn.1006-9895.22201.21082

        Abstract:During the Mei-yu period in the Yangtze River Basin, the precipitation is usually strong, per-sistent, and impacts a large region. It often leads to severe large-scale flood disasters. The in-ternal dynamic process of its persistency is worthy of further discussion. In this study, a case study is conducted on the large-scale persistent rainfall event in the Yangtze River Basin from July 5 to July 9, 2020, focusing on the interaction process between the latent heating and the circulation system during the rainfall event using the WRF model. The results show that an anticyclone anomaly is formed in the upper layers due to latent heating in the middle levels, favoring the eastward extension of the South Asian High (SAH). The eastward-extending SAH interacts with the Western Pacific Subtropical High (WPSH), resulting in WPSH west-ward extension, which modulates the wind and water vapor fields at the lower levels, provid-ing a favorable background field for heavy rainfall. Under the center of the condensation la-tent heating, a cyclone anomaly forms in the lower levels. This system helps to obstruct the northward migration of WPSH, thereby forming a stable WPSH, which is beneficial to main-taining the rainfall system in the Yangtze River Basin. The evolution of the East Asian sum-mer monsoon is characterized by apparent stagnation and northward jump, which is domi-nated by the activity of WPSH. This study shows that the release of large-scale condensation latent heat can help to form a more stable WPSH, which is beneficial to the Mei-yu persis-tency and may provide a possible self-maintaining mechanism of stagnation of the East Asian summer monsoon during the Mei-yu period.

      • SHI Zheng, LIN Xiaotong, TAN Yongbo, GUO Xiufeng, WANG Haichao

        Available online:January 05, 2022  DOI: 10.3878/j.issn.1006-9895.2110.21101

        Abstract:Based on an existing two-dimensional convective cloud model, this work is carried out to investigate the role of ice nuclei on dynamic, microphysical, electrification and charge structure in thunderstorm clouds by changing the concentration of ice nuclei. The results show that thunderstorm cloud develops ahead of time with the increasing of ice nuclei, and both updraft and downdraft velocities decrease. High ice nuclei concentration is conducive to the enhancement of heterogeneous nucleation process. A large number of ice crystals are formed in the high temperature region, while the homogeneous nucleation process is inhibited. Therefore, the overall content of ice crystals decreases, resulting in the decrease of graupel content in the low temperature region, and the size of graupel decreased in high temperature area. Therefore, the positive non-inductive electrification rate decreases and the negative non-inductive electrification rate increases. And because the liquid water content gradually decreases with the increase of ice nuclei concentration, the time for the polarity of charge carried by high temperature ice crystals to change from negative to positive is advanced. In the process of inductive electrification, the extreme value of inductive electrification rate gradually decreases due to the decrease of graupel particle size and the rapid consumption of cloud droplets. Because the ice crystals are preferentially generated in the high temperature region and are negatively charged, the space charge structure of thunderstorm clouds with different ice nuclei concentrations presents a negative dipole charge structure at the initial stage of thunderstorm cloud development. During the growing period of thunderstorm, with the increase of ice nuclei concentration, the space charge structure changes from three polarity to complex four order. In the dissipation stage of thunderstorm cloud, different cases show dipole charge structure, and the charge density decreases with the increase of ice nuclei concentration.

      • tanghuan, fushenming, sunjianhua, zhouxiangxian

        Available online:January 05, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21127

        Abstract:Tibetan Plateau vortex (TPV for short) is a kind of shallow mesoscale vortex system generated in the main body of the Tibetan Plateau. It occurs frequently, affects a wide range and causes strong disasters. It is one of the most important disaster-causing mesoscale systems in China. To fully reveal the statistical characteristics of TPVs is to lay the important basis for the study of TPVs. Among them, the accurate identification of TPVs is the key to the statistical characteristics of TPVs. With the emergence of reanalysis data with high spatial and temporal resolution, the study of TPVs has a better data basis. However, neither artificial identification method nor objective identification algorithm based on coarser resolution can be effectively applied to the current new reanalysis data. In this paper, a restricted vorticity based TPV identifying algorithm is proposed, which is suitable for high resolution reanalysis data. The method first determines TPV candidate points, divides multiple octants with the candidate points as the center, and determines the center of TPV by limiting conditions of average wind field in octants and counterclockwise rotation (the Northern Hemisphere ) conditions of octant group. The advantage of this approach is that the horizontal and vertical tracing of vortices can be detected quickly without complicated calculation and different thresholds for each pressure layer. A large sample evaluation of 15,466 TPVs (99,090 hours in total) in 42 warm seasons (May-September) from 1979 to 2020 shows that the average hit ratio of RTIA is more than 95%, the average false alarm ratio is less than 9%, and the average missing report rate is less than 5%. Therefore, the RTIA can accurately identify the centers of TPVs. In addition, the test results also show that when RTIA is applied to the reanalysis data with different spatial resolutions (e.g., 0.5°or 0.25°), the high accuracy of TPV identification can still be maintained. The identification results are mainly affected by the strength of vortexes themselves, and the identification accuracy of weak vortexes is lower than that of strong vortexes. This method can be used as a reference for the identification of other mesoscale vortexes.

      • YUAN Fang, Liao Jie, Zhou Zijiang

        Available online:January 05, 2022  DOI: 10.3878/j.issn.1006-9895.2110.21139

        Abstract:This paper proposes a comprehensive quality control (CQC) algorithm for the Chinese ground-based navigation satellite system (GNSS) water vapor products. The CQC algorithm consists of two sections: quality checks and comprehensive decision-making algorithm. The quality checks consist of 7 parts: limit check to eliminate errors that exceed reasonable limits, buddy check and low-pass filter check for better time consistency, neighboring station check, anomaly check and peak-valley value check for better spatial consistency, and background check to mark out data deviate from background field for assimilation application. After each check, the data that exceeds the threshold is marked, and then the comprehensive decision-making algorithm is used to score the marked data, and finally flag (correct, suspicious, or error) the data. Based on the quality-controlled observation data, the precipitable water vapor simulation of five sets of reanalysis data, including China"s first-generation global atmosphere reanalysis (CRA) product, were evaluated. The results show that the simulated total water vapor of all the reanalysis data in winter is slightly higher than the observation in winter and significantly lower than the observation in summer. Spatially, the simulated water vapor content in southern and western China is lower than the observation and this situation is more obvious in the summer half of the year. Relative to the observation, the average bias (B-O) of CRA is -0.633mm, and the root mean square error is 3.650mm. The deviation of CRA relative to observation is slightly lower than ERA-Interim but slightly higher than ERA5, which is significantly better than JRA55 and NCEP2 results.

      • Qiu Hui, ZHOU Tianjun, CHEN Ziming, ZHANG Wenxia, CHEN Xiaolong, LI Lijuan, LIN Pengfei

        Available online:January 05, 2022  DOI: 10.3878/j.issn.1006-9895.2111.21141

        Abstract:Based on the comparison with observation and reanalysis data, the study evaluated the performance of the Atmospheric Model Intercomparison Project (AMIP) and the Coupled Model Intercomparison Project (CMIP) historical experiments of IAP/LASG climate system model FGOALS-g3 in simulating climatology and interannual variability of JAS (July–August–September) seasonal-mean North Africa Summer Monsoon (NASM) and Sahel precipitation, and explained the bias by moisture budget and regression analysis, investigating the influence of ocean-atmosphere coupling by comparing AMIP and Historical. The results showed that both Historical and AMIP experiments underestimated precipitation, simulating weaker south west monsoon winds and a further south rainfall position. The pattern correlation coefficients of precipitation in Sahel and North Africa monsoon region simulated by AMIP are 0.80 and 0.62, respectively, which are larger than those of Historical, and the corresponding root mean square errors are 2.58 and 3.23, which are smaller than those of historical experiment, indicating that the deviation of AMIP is smaller than that of Historical. Considering the moisture budget diagnosis, Historical and AMIP both underestimated the water vapor convergence over NASM region, estimating less vertical moisture advection and evaporation and more horizontal moisture advection than observation, which led to dry biases. In terms of interannual variability, the observation shows that North Africa summer monsoon rainfall is negatively correlated with ENSO. AMIP can reproduce the ENSO-NASM negative relationship, which is stronger than observation. However, Historical cannot reasonably simulate the relationship at interannual time scale. AMIP overestimates the circulation response of ENSO, including descending anomalies, weakened tropical easterly jet and decreased low-level monsoon over North Africa, which contributes to the stronger precipitation negative anomaly. In contrast, Historical underestimates the above ENSO-related response, resulting in feeble precipitation negative anomaly. Moisture budget analysis indicated that vertical moisture advection anomalies, especially the dynamic term of vertical moisture advection anomalies, dominated the ENSO-NASM negative relationship. AMIP is coincided with observation, but it overestimates the above term, which leads to stronger negative rainfall anomalies. While Historical overestimates horizontal advection and vertical thermodynamic anomalies, which indicates that horizontal advection anomalies cause the inhibited simulation of ENSO-NASM negative relationship.

      • Cai Xuewei, Wan Ziwei, Wu Wenhui, Yangbo, Yi Zhihong

        Available online:January 05, 2022  DOI: 10.3878/j.issn.1006-9895.2112.21147

        Abstract:In order to improve the objective prediction ability of aircraft turbulence, a new aviation turbulence ensemble prediction algorithm based on Energy dissipation rate (referred to as EDR) is designed. The forecast value can be directly compared and verified with the new turbulence data (EDR) obtained by airborne detection, and the forecast intensity is not affected by the difference of the aircraft type. The algorithm calculates multiple forecast indexes representing Clear-Air Turbulence(CAT) and Mountain Waves Turbulence(MWT) using the basic meteorological elements of the Mesoscale Weather Numerical Forecast System of CMA(CMA-MESO) .Under the assumption that the predicted turbulence diagnostics and EDR observations both approximately follow normal distribution,According to the probability density matching relationship between previous forecast indexes and EDR observations,the original forecast index is converted into the forecast value with EDR in the real-time numerical forecast. Multiple forecast indexes are given different weights according to the forecast scores, and they are integrated into EDR turbulence forecast products including clear sky turbulence and mountain waves. Subjective and objective verification results show that this turbulence forecast product can roughly reflect the turbulence in different regions and types. The integration prediction of multiple algorithms is generally better than that of single index forecast.The resulting Relative Operating Characteristics(ROC) curves shows that the forecast results of light-or-greater turbulence increase the hit rate and reduce the false alarm rate, and it has high forecasting skills.

      • Niumiaomiao, Zhangjie

        Available online:January 05, 2022  DOI: 10.3878/j.issn.1006-9895.2108.21102

        Abstract:The daily grid precipitation data of National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC) is used to analyze the spatial-temporal change of extreme precipitation in the Tianshan Mountains from late spring to early summer (May and June) and the mechanism of Indian Ocean Basin Mode (IOBM) on extreme precipitation. The results show obvious spatial variations of extreme precipitation in the Tianshan Mountains from late spring to early summer. Extreme precipitation in the Western Tianshan Mountains significantly increased, while other regions hardly varied. The diagnosed and numerical simulation results consistently showed that the increase of extreme precipitation in the Western Tianshan Mountains related to the coetaneous positive anomaly of IOBM which promoted the convergence of warm and cold airflows in the Western Tianshan Mountains. On the one hand, the positive anomaly of IOBM strengthened the anomalous anticyclonic located in the eastern Europe to north central Asia which promoted the cold airflow southward transportation. On the other hand, it induced the non-uniform warming of Indian Ocean, which resulted abnormal vertical circulation and its subsidence caused the anticyclone anomalies in the Arabian Sea and the Indian peninsula. The anomalous anticyclone and southerly airflow jointly conveyed warm moisture from the Indian Ocean to the Western Tianshan Mountains, which was conducive to the increase of extreme precipitation in the Western Tianshan Mountains.

      • JIANG Qi, ZHANG Bihui, ZHAO Youlong, WANG fei, SUN Yele

        Available online:December 29, 2021  DOI: 10.3878/j.issn.1006-9895.2110.21142

        Abstract:Since 2013, the annual average mass concentration of PM2.5 in Beijing’s urban area has been decreasing year by year, but heavy PM2.5 pollution incidents have continued to occur frequently, and there are still many uncertainties in the causes and physical and chemical mechanisms of the rapid or even explosive growth of pollution. This study analyzes the thresholds of conventional meteorological elements, PM2.5 and its chemical components under three growth mechanisms of slow, rapid and explosive growth, as well as the correlation between the changes in meteorological elements and the increase in pollutant concentration from 2013 to 2020 in Beijing urban area. The results showed that from 2013 to 2020, the average accumulation rate of PM2.5 showed a trend of slowing down, and the proportion of slow growth in the accumulation phase of PM2.5 increased year by year in Beijing. Under the premise that the criterion is gradually strict, the proportion of explosive growth has not changed much year by year (4%—7%).The PM2.5 concentration threshold for an explosive increase from 2013 to 2016 was 62 μg m-3, and after 2017, the threshold was strict to 45 μg m-3. 82 μg m-3 is the threshold value that is extremely prone to explosive growth of PM2.5 since 2018. After this value, the probability of explosive growth will increase significantly. Organic aerosol (Org) played a vital role in the explosive growth. In the same time interval, the contribution of Org to the growth concentration of submicron aerosol species (PM1) is slow growth < fast growth < explosive growth, and the contribution of primary OA (POA) in rapid and burst growth to Org growth concentration on average exceeds 50%, which is higher than the average proportion of 40% during the study period. Among the inorganic components, the contribution of SO42? in increasing concentration of PM1 shows explosive growth (13%) > fast growth (11.8%) > slow growth (11.1%), while the contribution of NO3? is opposite. The contribution of secondary particulate matters (SPM) in the cumulative phase is higher than that of primary particulate matters (PPM), but in the explosive growth, the contribution of PPM to the pollution increase (up to 45%) is significantly higher than 33% in the average period, indicating that the contribution of PPM to the explosive growth cannot be underestimated. After the explosive growth began, the temperature decreased (0.2-1.2°C), while the humidity and pressure increased significantly in autumn and winter. The main air mass in the explosive growth is southward (the three heights account for 69%-82%), followed by the eastward direction (12%-20%) in Beijing urban area.

      • ZHANG Weiran, LIU Liping, WU Chong

        Available online:December 17, 2021  DOI: 10.3878/j.issn.1006-9895.2109.21050

        Abstract:An X-band phased array polarimetric radar (X-PAR) was deployed in Motuo during the second comprehensive scientific expedition to the Qinghai Tibet Plateau. The most advanced dual polarization phased array radar is used to continuously observe the precipitation in the valley area for the first time. In order to reveal the characteristics of precipitation in the southeast valley of the plateau, the monthly, diurnal and altitude variations of echo intensity and echo top height of precipitation in Motuo were quantitatively analyzed by using the observation data of Motuo X-PAR from November 2019 to October 2020. And the results are compared with those observed by Doppler radar in Naqu during the summer monsoon. The results show that: (1) the echo top height and area of Motuo are higher from April to September than from October to March, which indicates that the precipitation frequency is high and the convective precipitation is more in this observation period, especially in June. The increase of the proportion of weak echo leads to the echo intensity and strong echo frequency less than from October to March. According to the monthly variation characteristics of cloud precipitation, the year is divided into dry season and rainy season. Since April, the proportion of weak echo greatly increases, so that the echo intensity and strong echo frequency from April to September are less than those from October to March. According to the monthly variation characteristics of precipitation, the year is divided into dry season and rainy season. (2) The echo frequency, top height and area of precipitation in rainy season are larger than those in dry season, which indicates that the precipitation frequency in rainy season is higher and the convective activity is more vigorous. The diurnal variations of echo frequency, top height and area show that the strongest convection occurs in the afternoon in both seasons. The precipitation in the dry season mainly occurs in the afternoon and the first half of the night, and the precipitation in the rainy season mainly occurs in the second half of the night. (3) The echo intensity of precipitation in Motuo is mostly less than 30dbz. The echo frequency is higher in dry season when the altitude is more than 3km, and higher in rainy season when the altitude is less than 3km. (4) During the summer monsoon, the echo top height of Motuo is lower than that of Naqu, and the diurnal variation of echo top height and area is different from that of Naqu.

      • Dong Xinning, Wu Yao, Huang Anning, Tang Hongyu

        Available online:December 13, 2021  DOI: 10.3878/j.issn.1006-9895.2108.21032

        Abstract:Hourly precipitation data in the summer of 1991-2012 in Sichuan and Chongqing were used to analyze the spatial and temporal distribution characteristics of total precipitation and extreme precipitation, especially the diurnal variation characteristics of extreme precipitation. The results show that the total precipitation PA in Sichuan and Chongqing is mostly distributed like less in the west and more in the east for the influence of the terrain with higher west and lower east. Specifically, there are more precipitation in the eastern Sichuan basin and mountains of southwest of Sichuan, less in plateau of the northwest while more in the mountains around the Sichuan basin and less in the Basin. The precipitation frequency PF was higher in the west and lower in the east inversely, the higher PF in the plateau. The distribution of precipitation intensity PI is likely with that of PA which increases gradually from west to east. The spatial distribution characteristics of PA, PF and PI of extreme precipitation are similar to those of total precipitation. The greater precipitation in the eastern Sichuan basin such as Leshan, Ya"an, Dazhou and Guangyuan and in the mountains of southwest of Sichuan such as Xichang and Panzhihua are mainly due to the greater precipitation intensity. The larger precipitation in a small part of the southwest mountain in the north of Xichang is mainly due to the higher precipitation frequency. The less precipitation in the western plateau of Sichuan is due to the lower precipitation intensity. The daily peak of PA increased from west to east, while the daily peak of PF showed an opposite trend, decreasing from west to east. Almost all of them occur at night, and the "night rain" feature is very prominent. Most of the daily peaks in the higher altitude areas occur in the before midnight while lower altitude areas in the after midnight. The time of the daily peaks in the areas from west to east delays gradually which indicated the precipitation system spreading from west to east in Sichuan and Chongqing. The distribution characteristics of daily peak of extreme precipitation and its occurrence time are similar to the total precipitation. The threshold of hourly extreme precipitation in summer in Sichuan and Chongqing is lower in the west and higher in the east, and gradually increasing from the west to the east. The extreme precipitation frequency accounts for almost 40% of the total precipitation frequency, with no significant difference. The proportion of extreme precipitation in the total precipitation increased from west to east, and extreme precipitation contributed more to the total precipitation in the eastern than western of Sichuan and Chongqing. The spatial and time distribution of total precipitation is similar to that of extreme precipitation. The analysis of the diurnal variation of typical precipitation at four types shows that most plateaus and mountains in the western of Sichuan are type 1, which have the least precipitation but the highest precipitation frequency. A small mountainous area near Panzhihua and Sichuan Basin including Chengdu, Meishan, Ziyang and Neijiang are type 3, which have more precipitation. The central and eastern parts of Sichuan Basin and the eastern edge of Chongqing are type 4, which also have more and obvious transitional characteristics, with complex characteristics of three precipitation variables. Finally, the rest region including plateaus, mountains and the western part of the Sichuan Basin are type 2, which including Leshan and Ya "an areas with the most precipitation and have abundant precipitation and rainstorms in summer. The higher the altitude of the region, the greater the daily peak of PF at night. The PI of the type 1 region with higher altitude is obviously weak. The distribution of the three precipitation variables is in good agreement with the spatial distribution. The occurrence time of the daily peaks of the three variables was postponed from west to east from the first night to the next morning, and the occurrence time of the lower value was postponed from west to east from noon to the evening. The daily changes of extreme precipitation PA and PF all show a single-peak structure in the early morning, and the "night rain" features obviously, the daily peak occurs around 3:00 in the morning, the lower value near 13:00 in the afternoon, the PI shows a jagged structure which is lower between 5:00 and 11:00 and higher at the rest times. The PA lower value is mainly affected by PF while the peak value is mainly affected by higher PI and PF.

      • Yao Mengying, zhuzhiwei, YAO Junqiang

        Available online:December 13, 2021  DOI: 10.3878/j.issn.1006-9895.2111.21124

        Abstract:Based on the daily surface air temperature (SAT) gauge data and global reanalysis datasets from 1961 to 2016, we revealed interannual variability of SAT over Northwest China (NWC) in May and September via observational diagnosis and numerical simulations, and constructed their corresponding seasonal prediction models. The results show that: 1) The first modes of SAT over NWC during May and September are characterized by a similar homogenous spatial pattern but with different interannual variations. 2) The positive anomaly of SAT over NWC in May is related to the tropical zonal tripole anomalous convection (precipitation), corresponding to tropical SST anomaly during the decaying phase of La Ni?a. The extratropical teleconnection wave train excited by the tropical convection anomalies lead to barotropic anticyclonic (high pressure) anomaly over NWC, which increases the downward solar shortwave radiation and causes the increased local SAT. In September, the tropical zonal dipole convection (precipitation) anomaly that associated with the tropical SST anomaly during the developing phase of La Ni?a can trigger barotropic anticyclonic (high pressure) anomaly on the east and west sides of NWC, leading to positive SAT anomaly over NWC. 3) Based on the SSTA predictors associated with the decaying and developing phase of La Ni?a, the seasonal prediction model for SAT over NWC in May and September were established respectively. The prediction skill in terms of correlation coefficient during independent prediction period (2006-2016) can reach 0.74 (0.62) in May (September), which provides a reference for seasonal prediction of SAT over NWC.

      • ZHAO Jianqi, MA Xiaoyan, TIAN Rong

        Available online:December 10, 2021  DOI: 10.3878/j.issn.1006-9895.2111.21128

        Abstract:In this paper, WRF-Chem (Weather Research and Forecasting model with online coupled chemistry) model is employed to study the future changes of dust emission in Northern China. In order to improve the accuracy of the prediction results, the study comprehensively considers the influence of factors such as aerosols, greenhouse gases and vegetation fraction on the weather, climate and dust emission processes. The prediction shows, from 2016 to 2029, that the amount of dust emission in the northwestern dust source region is higher than that in the northern dust source region, and the differences of topography and climate lead to the differences of dust emission processes and their seasonal variations in the two regions. The seasonal mean dust emission fluxes in the northwestern and the northern from 2016 to 2029 show general decreasing trends, while some seasons show increasing trends. The dust emission flux in the northwestern shows a weak increasing trend in spring, and decreasing trends in summer, autumn and winter. The dust emission flux in the northern dust source region shows decreasing trends in spring, summer and winter, and a weak increasing trend in autumn. The variation trends of dust emission fluxes in the two regions are dominated by near-surface wind speed, while vegetation fraction, precipitation and surface temperature have important effects on the interannual fluctuation of dust emission fluxes.

      • Yang Chunsheng, Kou Leilei, Jiang Yinfeng, Chen Yao, Mao Ying, Wang Zhenhui

        Available online:December 09, 2021  DOI: 10.3878/j.issn.1006-9895.2109.21080

        Abstract:In order to obtain the best estimation of heavy precipitation, a priori model based on the multi-scale statistical characteristics of radar heavy precipitation data is very important. Based on the data of 180 independent precipitation events of Nanjing S-band Doppler weather radar from 2013 to 2016, this paper conducts wavelet decomposition to study the non-Gaussian edge distribution characteristics of the wavelet coefficients in the wavelet domain of the heavy precipitation radar echoes and the fractal characteristics between scales. And based on the prior statistical characteristics of heavy precipitation, a corresponding mathematical model was established. The research results show that for radar echoes with different precipitation structures presenting different shapes, their fractal parameters are not very different, and the directivity is not obvious, the wavelet coefficients of heavy precipitation can be uniformly modeled. Non-Gaussian features within intrascale can be represented by generalized Gaussian distribution, and fractal features between scales can be represented by exponential form. In order to further explain the relationship between the statistical characteristics of the heavy precipitation in the wavelet domain and the physical parameters of precipitation, the relationship between the fractal parameters of wavelet coefficients in the wavelet domain of heavy precipitation and environmental parameters is discussed. It is found that the correlation coefficient between the convective available potential energy and the fractal parameters in the environmental parameters (first-order horizontal direction) is 0.5535, and the correlation coefficient between the precipitation per hour and the fractal parameters (the mean of the second-order wavelet coefficients and fractal parameters in each direction) is 0.3848, while the correlations between other environmental parameters and fractal parameters is lower than 0.28. The statistical characteristics of heavy precipitation in the wavelet domain and the prior information with environmental parameters can be used for parametric modeling of heavy precipitation data. It has important reference value for subsequent applications such as optimal estimation of heavy precipitation, data assimilation, data downscaling, and multi-source data fusion.

      • xushiqi

        Available online:December 09, 2021  DOI: 10.3878/j.issn.1006-9895.2109.21003

        Abstract:Based on the daily precipitation data from 1961 to 2019 at stations in Northeast China (NEC), monthly mean data of NCEP/NCAR reanalysis, sea surface temperature (SST) data reconstructed by NOAA and outgoing long wave radiation (OLR) data, we analyzed climatic characteristics of early and late years of spring soaking rain (SSR) in NEC and the relationship with SST, especially tropical Indian Ocean SST forcing from the interannual time scale using statistical diagnostic methods. Results showed that there was a significant consistency between onset date of SSR and April precipitation, the onset date of typical SSR was concentrated in mid-late April during early years and in mid-late May during late years. If 500 hPa geopotential height fields over Northeast Asia in April showed a "- +" anomalous circulation distribution from west to east, with southerly winds and cyclonic circulation dominating in Northeast Asia, which were conducive to water vapour transport, SSR started early, and vice versa. Warm SSTA in tropical Indian Ocean during February-March was one of the important sources of stable influence on early years of SSR in NEC. Possible impact mechanism was that if Indian Ocean Basin warming (IOBW) in positive phase, it was favorable to anomalous anticyclone in Northwest Pacific during April, and the 500 hPa atmospheric circulation anomaly over Northeast Asia was similar to early years of SSR, the NEC situated in the right of 200 hPa westerly jet stream exit area, with enhanced vertical upward motion, then precipitation increased.

      • Xie Fei, Tian Wenshou, 张健恺, Lu Jinpeng

        Available online:December 09, 2021  DOI: 10.3878/j.issn.1006-9895.2104.21014

        Abstract:Based on the latest version of the Whole Atmosphere Community Climate Model (WACCM6) and the Data Assimilation Research TestBed (DART), this paper develops an assimilation interface for temperature, ozone, and water vapor data in the middle and upper atmosphere, and builds an assimilation model with complete stratospheric processes that includes Assimilation, Weather Forecasting and Short-Term Climate Prediction System. The system performs assimilation simulations of the stratospheric atmosphere in March-April 2020 and provides 0-3 days, 4-15 days and 16-30 days forecast and 31-60 days short-term climate prediction for the stratospheric atmosphere changes in May-June using the assimilation analysis field as the initial value. The results show that the system can reflect the time evolution of the very unusual ozone depletion event in the Arctic stratosphere in March and April 2020, which is very close to the Microwave Limb Sounder (MLS) satellite observations; while the simulations without assimilation can simulate the Arctic ozone depletion event, the magnitude of ozone depletion is much smaller than that of the MLS satellite. The assimilation model system not only improves the simulation of the chemical composition of the Arctic stratosphere, but also provides better simulations of the Arctic stratospheric temperature and circulation changes. The simulated March-April and predicted May-June Arctic stratospheric temperature and latitudinal wind variability are in good agreement with the results of Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA2) reanalysis with assimilation. The RMSE between the simulated March-April and the predicted May-June Arctic stratosphere temperature and wind and the MERRA2 reanalysis data are ~3 K and ~4 m/s in most regions, respectively. On a global scale, this system has the most significant improvement in the simulation of the middle and lower stratosphere, with the RMSE in the prediction results reduced by more than 50% compared to the prediction results of unassimilated simulation experiments.

      • liushijia, zhoutianjun, 左萌, 巫明娜

        Available online:December 09, 2021  DOI: 10.3878/j.issn.1006-9895.2110.21083

        Abstract:Moist adiabatic processes in the tropics amplify the surface warming, producing a warming peak at about 200hPa, known as the “tropical tropospheric amplification”. As one of the most remarkable feature of climate change, tropical tropospheric amplification is an important metric in evaluating the model performances. In this study, based on the RSS4.0 satellite data and the ERA5.1 reanalysis data, we systematically assess the ability of Version 3 of the Flexible Global Ocean-Atmosphere-Land System model (FGOALS-g3) in simulating the temperature change, especially the tropical tropospheric amplification, and reveal an improved simulation skills of the latest version FGOALS-g3 compared with its previous version FGOALS-g2. By comparing the results of the historical simulation of FGOALS-g3 with the simulation from its atmosphere component the Grid-Point Atmospheric Model of LASG-IAP (GAMIL3), the role of air-sea coupling is studied. The results show that FGOALS-g3 can reasonably reproduce the observed significant global tropospheric warming, but with a stronger trend which is related to the internal variability of the climate system and the differences in historical external forcing used by the two generations of climate system models. FGOALS-g3 has also performed well in simulating the observed vertical profile of the mean tropical warming and the spatial distribution of the tropical tropospheric amplification, while has a positive bias in simulated magnitude of the tropical tropospheric amplification, resulting from stronger temperature change in the lower troposphere. Compared with FGOALS-g2, the improvement in FGOALS-g3 is mainly manifested as an increased response to volcanic aerosol forcing, a more reasonable spatial pattern of the amplified tropical troposphere and the vertical profile of mean temperature trend. Although GAMIL3 simulation fails to present the influence of external forcing changes on the tropospheric warming trend due to a lack of air-sea coupling process, leading to the biases in the long-term trend simulation, it reasonably captures the interannual variability since it is driven by the observed sea-surface temperature.

      • TIAN Jia, YANG Shuangyan, LIU Yashu

        Available online:December 09, 2021  DOI: 10.3878/j.issn.1006-9895.2108.21106

        Abstract:Based on China"s high-resolution grid rainfall data, NCEP/NCAR and ERA-Interim reanalysis data from 1979 to 2018, the relationship between the interannual variation of the main mode (southern concentrated pattern) of the quasi-biweekly oscillation (QBWO) of diabatic heating over Tibetan Plateau (TP) during boreal summer and rainfall anomaly over eastern China is investigated. In the year when the interannual intensity of QBWO over TP is strong, there is a significant positive correlation between summer rainfall anomaly in the south of the Yangtze River and QBWO over southern TP; in the weak years, the rainfall anomalies in the Jianghuai region and South China characterize a dipole pattern. In addition, in the strong (weak) years, the low-latitude intraseasonal signal originating in the Northwest Pacific region mainly shows a westward (northwestward) propagation, and the mid-high-latitude quasi-barotropic intraseasonal signal mainly shows a southward (southwestward) propagation. The combined effect of the signals from low latitudes propagating westward (northwestward) and the signals from mid-to-high latitudes propagating southward (southwestward) cause different abnormal rainfall patterns in China. The low-latitude QBWO signal propagating westward (northwestward) weakens and disappears after reaching the Arabian Sea (southeast of TP). The southward (southwestward) signal in the mid-high-latitude converges with the westward (northwestward) signal in the low-latitude, and then continues to propagate westward, and finally weakens and disappears.

      • YU Yueyue, ZHANG Lingli, GUAN Zhaoyong, YANG Wenwen

        Available online:December 06, 2021  DOI: 10.3878/j.issn.1006-9895.2111.21143

        Abstract:Based on the nationwide records of cold weather hazards combined with the high-precision reanalysis data NASA MERRA2 during wintertime (November-March) in the period of 1980-2020, a daily dataset of low-temperature disasters (low temperature, abrupt temperature drop, freezing, rain&snow, and snowstorm) in China has been constructed. Using linear trend analysis, ensemble empirical mode decomposition (EEMD) method, and wavelet analysis, the temporal and spatial distribution characteristics of various kinds of cold hazards in China are studied. Results show that cold hazards without precipitation (low temperature, abrupt temperature drop, and freezing) are often co-caused by two or more kinds of cold hazards, while cold hazards with precipitation (rain&snow and snowstorm) are mostly caused by a single kind. The occurrence frequency of different kinds of cold hazards has significant regional and seasonal differences: the low temperature hazard had the widest affected area in January, and the occurrence frequency presents a "high-low-subhigh" distribution pattern from south to north; The frequency of abrupt temperature drop hazard occurred the most in December, whose occurrence frequency is "high in the East and low in the west"; Rain& snow hazard occurred most in southern China from January to February; The occurrence of snowstorm hazard is significantly more frequent than the other four kinds of cold hazards, mostly distributed in susceptible regions such as pastoral areas. As far as the whole country is concerned, the frequency and affected area of most cold hazards (except snowstorm) show a long-term increasing trend. The snowstorm hazard, however, has an increasing trend in the affected area, mainly contributed from January, and a decreasing trend in the frequency, mainly contributed from March. The interdecadal variability of the occurrence and affected area of most cold hazards (except snowstorm) increased after 2000s, while the interdecadal variability of snowstorm is greater before 2000s; The interannual variability of the frequency of cold hazards (except snowstorm) increased significantly after 2005. For single-kind disasters, only the affected area of abrupt temperature drop hazard showed a significant increasing trend, mainly due to January. For the compound-kind cold hazards, the combination of abrupt temperature drop and cold hazards with precipitation increased significantly.

      • Sun Siyuan, Guan Zhaoyong

        Available online:November 30, 2021  DOI: 10.3878/j.issn.1006-9895.2106.21006

        Abstract:Abnormal heavy precipitation during the Meiyu period (June-July) in 2020 brings great economic property losses and human casualties to the middle and lower reaches of the Yangtze River, and the length and intensity of precipitation in this Meiyu period are far exceeded the historical average. Using daily NCEP/NCAR reanalysis data and CPC global daily precipitation data, the features of heavy precipitation and its relationship with baroclinic Rossby wave in the upper troposphere is investigated in this paper. The results show that the total precipitation and precipitation anomalies in the middle and lower reaches of the Yangtze River are located in the southern part of Anhui Province, and there are seven consecutive precipitation processes. In the middle and lower reaches of the Yangtze River, there is convergence in the middle and lower troposphere accompanied by dispersion in the upper troposphere, and there is strong anomalous upward motion over the region, which is favorable to the development of anomalous heavy precipitation. At the same time, water vapor is transported from the Bay of Bengal and the South China Sea to the middle and lower reaches of the Yangtze River, which provides sufficient water vapor for the occurrence of heavy precipitation. When the standardized time series of daily precipitation in this region were analyzed by using wavelets, significant cycles of 2-4 day and 6-14 day are found. The Rossby fluctuations shown by high frequency (2-14 day) perturbations exhibit a downstream dispersion in the upper troposphere, with fluctuations originating near Lake Baikal. The propagation process of the fluctuations downstream shown by the wave disturbance energy and flux is more consistent with that of the wave packet. The wave disturbances originating near the Mediterranean Sea and Lake Baikal, respectively, can disperse eastward or southeastward to the middle and lower reaches of the Yangtze River. The energy transmitted to the middle and lower reaches of the Yangtze River favors the intensification of the disturbance in this region and thus the occurrence and maintenance of heavy precipitation. The above results improve the understanding of the causes of the super-long "violent Meiyu" in 2020 and may provide clues for effective prediction of similar events.

      • Shen Xinyong

        Available online:November 30, 2021  DOI: 10.3878/j.issn.1006-9895.2108.21045

        Abstract:This paper uses the 1°×1° reanalysis data provided by NCEP/NCAR, and uses the WRF4.0 mesoscale numerical model to simulate the upscale process of a squall line in South China on April 13, 2016. In order to further study the role of topography in the upscaling process of the squall line, this paper designs a series of sensitivity tests to study in detail the influence of Nanling on the upscale growth of the squall line and its possible mechanism. The WRF model better simulates the changes before and after the squall line crossing the mountain and the distribution of its precipitation. Strong convection develops more strongly after crossing the mountain than before crossing the mountain, and the horizontal scale grows faster, but the terrain sensitivity tests at different heights show that a suitable terrain height is more beneficial to the development of storms. The topography affects the scale and organization of the squall line, and the high topography disperses the convection in the north of Guangdong . Terrain can indirectly affect the distribution of convective cells and the strength of convective cells in the squall line by changing the horizontal flow field, water vapor field, vertical movement, and vertical wind shear at the lower level, which are mainly reflected in the following: no terrain obstruction is beneficial to the jet stream ,and it is more convenient to transport water vapor in the northward direction; a certain terrain height is beneficial to the vertical movement of the low level, while the terrain is too high to facilitate the vertical movement of the upper level, and the low level is more likely to be mainly detoured; when the terrain exceeds a certain height, the low-level convergence field is correspondingly weakened.

      • ZHANG Jingping, FU Shenming

        Available online:November 23, 2021  DOI: 10.3878/j.issn.1006-9895.2111.21178

        Abstract:Mesoscale vortex (MV) is one of the most important weather systems that causes precipitation and meteorological disasters in China. However, there is no universal standard of MV identification , and the MV objective identification is still an urgent problem to be solved. Based on the main features of MVs in China, a new objective identification algorithm (new algorithm for short) suitable for high-precision grid data is developed in this study, by combining the wind and vorticity. The new algorithm can accurately identify the mesoscale cyclonic circulation and locate the vortex center, with lower false rate and higher positioning accuracy than existing identification methods. The new algorithm is applied to three kinds of mesoscale vortices (Plateau vortex (TPV), Southwest vortex (SWV) and Dabie Mountain vortex(DBV)) frequently occurring along the Yangtze river basin, the results show that the new algorithm performed well in all the three kinds of MVs with almost insensitive to applied period or data resolution (6-hourly 0.5°×0.5°NCEP CFSR reanalysis data, hourly 0.25°×0.25°ERA5 reanalysis data). Based on the DBV activity dataset of DBV (the total DBV occurrence is 36357 ) in the warm season (May - September) during 1979 - 2020, the new algorithm is quantitatively evaluated. The evaluations prove that the new algorithm can identify MV in a long-term and stable way, with an average hit rate of 95.5%. In addition, this paper proposes a 3D MV tracking scheme, which has significant advantages over traditional tracking methods.

      • Zhao Chuo, Xu Guo Qiang

        Available online:November 23, 2021  DOI: 10.3878/j.issn.1006-9895.2111.21110

        Abstract:The lightning data of FY-4A satellite and ADTD (Active Divectory Topology Diagrammer) are significant for the study of rainstorm and severe convection weather. This paper compares and analyzes the difference between the two lightning data through a case study of rainstorm in MianNing, SiChuan Province, a series of numerical experiments are designed to introduce two kinds of lightning data into the numerical prediction model. The main conclusions show as follows:(1)Two kinds of lightning data have different detection effect in different areas. The ADTD lightning data are more extensive and scattered, and the number and distribution of lightning detected by FY-4A satellite are more intensive. There is a good consistency between the two kinds of surrogate radar echo transformed by two kinds of lightning data . For low frequency lightning, the ADTD lightning localizer may be more efficient than Fy-4A LMI. (2)The introduction of these two types of lightning data has positive effects on precipitation forecast, and the application of ADTD lightning data is more effective for improving the accuracy of short-time precipitation forecast.(3)The two types of lightning data have different effects on the adjustment of cloud microphysical quantities in different regions. This shows that the distribution of the two types of lightning data is not completely consistent, and it shows that the two types of lightning data are complementary to each other.

      • liushijun, yangrongkang, caoxiaozhong, guoqiyun

        Available online:November 18, 2021  DOI: 10.3878/j.issn.1006-9895.2110.20252

        Abstract:The round-trip horizontal drift observation is a new type of observation method being studied and implemented in China. It can effectively improve the observation efficiency and economic benefits, and is of great significance to overcome the defects of conventional radiosonde observation and improve the quality of numerical prediction. In this paper, according to the characteristics of thermal and dynamic processes and their main influencing factors in the rising and horizontal drift stages of sounding, a theoretical model of thermodynamic of horizontal drift on sounding system is established, and the reliability of the theoretical model is further analyzed and verified by combining with the actual observation test. The research results have important theoretical support and practical value for the design and improvement of the round-trip drift sounding system.

      • Wang zeyi, Chen Xiaolong, Zhou Tianjun, Zou Liwei, Li Lijuan, Lin Pengfei, He Linqiang

        Available online:November 17, 2021  DOI: 10.3878/j.issn.1006-9895.2110.21144

        Abstract:The seasonal evolution of the Asian monsoon precipitation is crucial to Asian agriculture production and social economy. Based on the observations, we assess the performances of latest version of the IAP/LASG Flexible Global Ocean-Atmosphere (FGOALS-g3) compared with FGOALS-g2 in simulating the Asian monsoon seasonal evolution. Compared with a atmospheric experiment driven by historical monthly mean FGOALS-g3 SST, the influence of air-sea coupling on monsoon seasonal evolution is also studied. The results show that FGOALS-g3 has improved the ability to simulate the precipitation annual cycle in South Asia and the Northwest Pacific region which may be relevant to single atmospheric models, but does not improve in other regions. The biases of precipitation annual cycle and timing of monsoon from South Asian to Northwest Pacific and precipitation annual cycle in South East Asian are improved by air-sea coupling process. Compared with FGOALS-g2, the ability to simulate Northwest Pacific monsoon onset and withdrawal, Arabian Sea monsoon withdrawal and from Indian Peninsula to the South China Sea monsoon peak are significantly improved in FGOALS-g3. The delayed bias onset in South Asia and Indo-China Peninsula is increased in FGOALS-g3 relative to FGOALS-g2, which is associated with weak Somali jet caused by dry bias in African land at May. In the Northwest Pacific, the bias of monsoon onset simulation (delayed in the West and advanced in the East) is significantly reduced in FGOALS-g3, mainly because the SST bias in tropical Pacific is improved, and the local Hadley circulation is strengthened, resulting in anomalous subsidence in the region, which reduces the wet bias in January on the west side, the relative precipitation increases, and the improvement of wet bias in the East is the result of compensation between the dry biases in May and January. The improvement of the tropical SST pattern in the coupled model has great implication to improve the simulation ability of the Asian monsoon precipitation annual cycle.

      • Xiong Defang, Peng Jingbei

        Available online:November 17, 2021  DOI: 10.3878/j.issn.1006-9895.2110.21133

        Abstract:This paper investigates the flooding events caused by heavy precipitation and the corresponding 15 heavy rainfall events in the Sichuan-Chongqing area in the summer of 2020 year and compares them with the situation in the 2006 drought year. In the summer 2020, the western Pacific subtropical high (WPSH) was stronger compared with its climatological mean, and its western edge was beyond 110°E which is to the west of its climatological position. Since the Qinghai-Tibet high extended eastward and was strong, the upper and lower layers worked in concert to maintain the WPSH steadily. The cold air that causes precipitation in the Sichuan-Chongqing region mainly comes from short waves in the westerlies. The short waves in the mid-latitudes were frequent and influenced the region. Due to the joint influence of the southwesterly flows on the western flank of WPSH, and the northerly wind, the Sichuan-Chongqing region forms an area of major water vapor flux convergence. It provides most favorable water vapor conditions for the occurrence of heavy rainfall events. Furthermore, the monsoon air stream, traveling from northern India to the east side of the plateau, arounds the south side of the plateau and transports water vapor eastward, forming another important water vapor channel. The year 2006 is a typical drought year of the Sichuan-Chongqing region, when fewest heavy rainfall events occurred. In this year, the WPSH is easterly, the short-wave trough in mid-latitude westerlies is not active, the southwest monsoon is weaker, and the water vapor convergence in the Sichuan-Chongqing region is less, which are in sharp contrast with 2020.

      • Mao Jiashen, Chen Yilun, Zhang Aoqi, Chen Shumin, Fang Rong, Li Weibiao, Li Mingxue

        Available online:November 17, 2021  DOI: 10.3878/j.issn.1006-9895.2110.21116

        Abstract:Using the raindrop spectrum observation data from Chongzuo National Meteorological Observatory and Fangcheng National Reference Climate Station, combined with the rainfall data and radar observation data, we analyzed the structural characteristics and differences of raindrop spectrum at different precipitation stages on the inland leeward side (LSI) and near-coast windward side (WSC) during the impact of typhoon Wipha from August 2 to 3, 2019. The results show that the rainfall of typhoon Wipha is mainly contributed by medium and small raindrops; especially the contribution of medium raindrops is stable above 70%. The rainfall at LSI is dominated by stratiform clouds with relatively gentle rain intensity, while the rainfall at WSC is characterized by mixed cumulus clouds with large rain intensity and severe fluctuations. Due to the strong convective activity and upward motion, the raindrop number concentration and raindrop diameter at WSC are significantly larger than those at LSI. The main factor for the increase of rain intensity at LSI after typhoon landfall is the increase of raindrop diameter, while the increase of rain intensity at WSC after the change from typhoon eye wall to strong convective spiral rain band is mainly due to the increase of raindrop number concentration. The average mass-weighted mean diameter of the convective precipitation of typhoon Wipha is 1.85 mm and the average logarithmic normalized intercept is 3.95 mm-1·m-3. The convective precipitation at LSI is located in the maritime convective region, while at WSC it is between maritime and continental convection.

      • qinhao, wuliquan, hehui

        Available online:November 17, 2021  DOI: 10.3878/j.issn.1006-9895.2108.21108

        Abstract:Using the monthly precipitation data of 160 stations in China, Hadley Center sea surface temperature (SST) data, NOAA outgoing longwave radiation (OLR) data and NCEP/NCAR reanalysis data from 1979-2019, the impact of the summer tropical Atlantic sea temperature (TAST) on the first rainy season precipitation in South China (FRSP) is investigated. Base on the correlation analysis and information flow theory, the results show that the increase (decrease) of previous summer TAST partly leads to the decrease (increase) of FRSP. The SST rising in the key region (35°W-10°E, 10°S-5°N) can enhance the Walker circulation and induces an anomalous subsidence over the Pacific, which lead to an easterly wind anomaly over the central and western equatorial Pacific in summer. The ocean-atmosphere interactions promoted the development of La Ni?a in the following autumn and winter. The same mechanisms act for the negative SST anomaly but with opposite sign, and conducive to the development of El Ni?o. When the La Ni?a(El Ni?o)reach its peak in winner, the convection heating intensify (suppressed) in the western Pacific which triggered abnormal cyclones (anticyclones) response in the lower troposphere to its north. The anomalies persist until the first rainy season in second year, causing the abnormal cyclones (anticyclones) maintained which, on the one hand, is conducive to the weakening and eastward retreat (strengthening its westward extension) of the Western Pacific Subtropical High (WPSH), thus reducing (increasing) the transport of water vapor from the South China Sea to South China. On the other hand, the convective activity (suppression) in tropical areas is conducive to strengthening (weakening) the local Hadley circulation, resulting in the subsidence (ascent) anomaly in South China, and suppressing (intensifying) the convection. In addition, the negative (positive) SST anomaly in the eastern Pacific excited a Pacific-North American (PNA) like wave train, and the SST anomalies in the North Atlantic further activates the Eurasian (EU) wave train that making the Eurasian mid-high latitudes region shows negative (positive)-positive (negative)-negative (positive) geopotential height anomalies, which is unfavorable (favorable) for the cold air affecting South China, and eventually cause FRSP negative (positive) anomalies.

      • Yu Han, Zhang Hongbo, liu dong-xia, 袁善锋, 王东方, 卢晶雨

        Available online:November 17, 2021  DOI: 10.3878/j.issn.1006-9895.2101.20243

        Abstract:Based on the three-dimensional lightning location data from Beijing Broadband Lightning Network (BLNet) and the S-band Doppler radar, the relationship between lightning activity and the intensity of the radar reflectivity of seven severe squall line, occurred in Beijing from the year of 2015 to 2017 were analyzed. The results show that lightning flashes are mainly located in the convective leading line and centered in the strong echo region with reflectivity greater than 30 dBZ, and a small part of lightning flashes distributed in the trailing stratiform region. Based on the three-dimensional lightning structure, the lightning flashes are mostly concentrated in the range of 6~11 km height layer. Using radar echo volume with reflectivity >30 dBZ (V30dBZ) between 0 and -30℃ level, as a strong convection index to reflect both the depth and area of strong convection, we found that, of all seven squall lines, the trend of the lightning frequency and V30dBZ evolution showed some relationship, for five of them, the peak of lightning frequency is the same or earlier than that of the V30dBZ , and the lagged correlation coefficient of them is higher than 0.61, the lightning frequency is earlier than V30dBZ with a leading time from 0 to 96 min. As for the other two cases, the lightning frequency peak lag behind the V30dBZ at 30 and 60 min respectively. The results are significant not only for understanding lightning activity and convection intensification, but also provide scientific basis for lightning data assimilation in the numerical weather prediction.

      • LIU Fan, ZHANG Jinru, LIU Jing, YANG Lianmei

        Available online:November 12, 2021  DOI: 10.3878/j.issn.1006-9895.2110.20220

        Abstract:Based on Two Dimensional Video Disdrometer, combined with cloud radar, wind profile radar, microwave radiometer, GPS/MET water vapor and other vertically-scanning instruments, the microphysical characteristics of a cold front snowstorm in The West Tianshan Mountain on February 18-19, 2020 were analyzed and studied. A classification algorithm for snowflake and graupel is designed to quantitatively study the microphysical characteristics of snowfall. The results show that :(1) In the cold front invasion and dynamic forcing stage, the precipitation particle type is mainly snowflake, and the microphysical process is deposition and aggregation; (2) In the stage of cold front control bring wind chill, precipitation particles are snowflake, graupel, and the microphysical processes is aggregation and riming, and aggregation is positive impact to riming; (3) In the passage of the cold front, due to the rise of cloud top temperature, less ice nucleation and enough subcooled water favor the riming. Different from the Nanjing, snowflake diameter and snow intensity in the West Tianshan Mountains are smaller, but graupel have a greater contribution to the snow intensity. The raindrop size distribution and gamma distribution are fitted by two melting models, which are similar to the characteristics of local stratiform cloud precipitation.

      • Zhang Haiyan, Tao Li, Xu Chuan

        Available online:October 20, 2021  DOI: 10.3878/j.issn.1006-9895.2107.21012

        Abstract:This study explores the characteristics of interannual and interdecadal air-sea interaction related to Pacific Decadal Oscillation (PDO) over the different regions of the North Pacific based on the relationship between turbulent heat flux anomalies and sea surface temperature (SST) anomalies during 1958-2018. The results show that the atmosphere drives directly SST anomalies over the Kuroshio-Oyashio Extension (KOE), and the SST anomalies forces atmospheric circulation over the equatorial central and eastern Pacific on the interannual scale. On the interdecadal scale, it shows SST anomalies are mainly driven by atmospheric circulation over the north center of PDO. But ocean is very important in forming SST anomalies off California coast. Further analysis shows that the area off California coast is one of the key areas of quasi-12a oscillation in the North Pacific. The period is similar to the decadal oscillation of PDO. The anticyclone (cyclone) circulation off California coast may be forced by the cold (warm) SST anomalies off California coast. The upwelling of the equatorial central Pacific and the meridional wind stress anomalies in the subtropical eastern North Pacific are the other two important parts in the quasi-12a oscillation in the North Pacific.

      • fuzhilong, liguoping

        Available online:October 19, 2021  DOI: 10.3878/j.issn.1006-9895.2110.21054

        Abstract:Based on the houly precipitation data from automatic weather stations,FY-2G TBB data and ERA5 reanalysis data, dynamic analysis and numerical experiment are carried on for a warm-sector mountain rainstorm event in Western Sichuan Basin on 23 July 2017. The results indicate that the warm-sector mountain torrential rainstorm occurred in the edge of the WPSH (West Pacific Subtropical High) under the background of weak synoptic forcing. The conditions of high temperature and high energy in Western Sichuan Basin and the southeast wind intruding into the basin, lifted by Longmen Mountain, which is the inducements of this rainstorm.The conversion of the mountain-plain circulation is the reason for the intensification of rainstorm and the reorganization of mesoscale convective cloud clusters. It is the mountain-plain circulation uplifting the background wind that causes the upward sloping motion. A further study of numerical simulation show that the mountain-plain circulation is driven by near-surface thermal perturbation. In the daytime, there is positive virtual temperature disturbance area in the hillside of Western Sichuan Basin, and a plain-to-mountain flow has developed. After sunset, the distribution of the virtual temperature disturbance on the mountain and plain is reversed. Therefore, the mountain - plain circulation is shifted from mountain to plain. When the model surface heat source was removed, the near-surface thermal perturbation tends to disappear, and the mountain-plain circulation could not be formed in the Western Sichuan Basin. Consequently, the convergence area related to the mountain-plain circulation dissipated, resulting in the obvious decline of the simulated cumulative precipitation and the disappearance of the heavy precipitation center.

      • ZHANG Chunyan, WANG Donghai, PANG Zihao, JIANG Xiaoling, MA Qianhui

        Available online:October 19, 2021  DOI: 10.3878/j.issn.1006-9895.2110.21078

        Abstract:This study sets up a long-term (2013-2017) dynamically and thermodynamically consistent atmospheric dataset over the Tibetan Plateau-Naqu analysis region. This dataset is derived by the constrained variational objective analysis with ground-based, sounding, and satellite measurements as well as ERA-Interim reanalysis data. Using averaged results from this five-year dataset, the annual evolutions of the atmospheric basic environments, cloud-precipitation, and large-scale dynamic and thermal structures in the Naqu analysis region are analyzed. The results show that: 1) the seasonal variation of wind speed above 350 hPa is significant, with a maximum (> 50 m/s) from November to February in the next year, and the vertical variation of wind speed is the weakest while that of temperature is the strongest from July to August. The high humidity area is located at 350 - 550hPa in summer and autumn but at 300 - 400 hPa in winter and spring. 2) The precipitation in the analysis region is rich from June to early July. In spring, autumn, and winter, the layer of 300 - 400hPa (as the junction of atmospheric ascending and descending motion) is the cloud concentration area. But in summer, the enhanced atmospheric ascending convection and water vapor lead to an increase of total and high clouds whereas a decrease of medium and low clouds. 3) The surface latent heat flux and the total air-column latent heat are the strongest whereas the air-column net radiative cooling is the weakest in summer. The strong surface sensible heating in the plateau leads to the horizontal warm advection below 500hPa, while the strong westerly and radiative cooling cause the cold advection above 500hPa. In addition, the analysis region is characterized by dry advection in the whole year, however, there is a weak moist advection in summer. 4) The apparent heat source Q1 has obvious vertical stratification characteristics, that is, showing diabatic cooling below 500 hPa and diabatic heating in 300 - 500 hPa and 100 - 150 hPa in the whole year; while the layer of 150~300 hPa has diabatic cooling in the dry seasons (winter and spring) and diabatic heating in the wet seasons (from the end of spring to autumn). In summer, the entire air column is almost dominated by diabatic heating because of the enhanced ascending motion, net latent heating, the transport of sensible heat by rising turbulence, and the existence of high clouds.

      • Fan Wenlu, Jing Xiaoqin, Yang Jing, Zhou Siyu

        Available online:October 18, 2021  DOI: 10.3878/j.issn.1006-9895.2107.21046

        Abstract:Microphysical characteristics in mixed-phase stratiform and convective clouds are very different, but have not been well considered in numerical models. This is one of the sources leading to uncertainties in modelling clouds and precipitation. In order to improve our understanding on the difference in microphysics between mixed-phase stratiform and convective clouds, and to provide quantitative results for model evaluation and parameterization, The microphysical characteristics of continental mixed-phase winter stratiform and summer convective clouds in the mid-Rocky Mountain region are compared using data collected during the Ice in Clouds Experiment—Layer Clouds (ICE-L) and the High Plain Cumulus (HiCu) project. The particle images and particle size distributions (PSD) were measured using 2D-Cloud and 2D-Precipitation probes, the liquid water content (LWC) was measured using the King hot-wire probes, and the ice water content (IWC) is calculated based on the particle spectrum. The main findings are: (1) Between -30° and 0°C, the LWC in the summer convective clouds is an order of magnitude higher than that of the winter stratiform clouds, and the IWC in the summer convective cloud is 1-2 orders of magnitude higher. More supercooled liquid water was observed near the convective cloud top. The LWC in summer convective clouds increases with decreasing temperature from 0°C to -20°C, while the LWC in winter stratiform clouds varied in an opposite way. The liquid fraction in the summer convective clouds is smaller than that of the winter stratiform clouds, suggesting more rapid ice production. (2) Both the winter stratiform and summer convective clouds had large spatial variability in their phase distribution. As the temperature decreases from 0°C to -30°C, ice in the winter stratiform clouds grew through the Bergeron process, and the water-dominated zones transform to the mixed-phase and ice-dominated zones. The phase distribution was more complicated in summer convective clouds, suggesting complicated liquid-ice interaction. (3) The ice PSD in summer convective clouds was broader than that in winter stratiform clouds between 0°C and -30°C. As the temperature decreases, the ice PSDs in both winter stratiform clouds and summer convective clouds broadened. (4) The observed particle images in winter stratiform clouds were irregular at temperatures lower than -20°C, while between -20~-10°C the ice were dendrites and irregular, and at temperatures warmer than -10°C the ice were mainly needles, columns and irregular, indicating the ice grew through vapor diffusion and coalescence in winter stratiform clouds. In summer convective clouds, the ice mainly formed through drop freezing, riming and coalescence. (5) In stronger updrafts of summer convective clouds, higher LWC and liquid fraction were observed. The IWC had no obvious correlation with vertical velocity, indicating the efficiency of glaciation in HiCu clouds was not dependent on vertical velocity.

      • renzikun, zhoutianjun, guozhun, chenxiaolong, lilijuan, wubo

        Available online:October 12, 2021  DOI: 10.3878/j.issn.1006-9895.2109.21098

        Abstract:Based on the LASG/IAP developed general circulation model GAMIL2 (G2) and GAMIL3 (G3), the simulation ability of tropical precipitation and convective vertical structure was evaluated, and the reasons for the improvement of precipitation simulation and the relationship between the vertical structure of tropical convection and precipitation simulation deviations were explored. Both versions of GAMIL precisely capture the main characteristics of tropical precipitation, while G3’s simulation are globally accurate than G2. The main improvement of the new version is to significantly reduce the positive precipitation bias in the tropical northwest Pacific Ocean. The water vapor budget diagnosis shows that the precipitation deviation mainly come from the evaporation term and the vertical advection dynamic term, and the latter comes from the combined effect of intensity of vertical motion and the vertical motion profiles. The vertical structure deviation of convection mainly exists in equatorial Indian Ocean and equatorial Atlantic Ocean areas, which mainly corresponds to weaker convergence component in lower atmosphere and higher altitude of detrainment. In the tropical northwest Pacific and equatorial Eastern Pacific, the typical “top-heavy” and “bottom-heavy” characteristic of the vertical motion profile are well represented, but the deeper convection than reanalysis data is still eminent. The wet static energy (MSE) budget shows that the excess net energy flux over the tropical Northwest Pacific is the main source of the modeled vertical motion deviation. However, the deeper vertical convective structure results in a larger gross moist stability (GMS), which offset the net energy flux deviation and inhibited the simulated convective intensity. the significant improvement of precipitation simulation in the tropical northwest Pacific in G3 Is mainly due to the reduction of positive deviation of convective intensity. The down-regulation of convective threshold and stratus threshold in G3 increase the frequency of convection and inhibits excessive intensity of vertical motion. The vertical structure of tropical convection has various and close relationships with precipitation deviation, which should be paid more attention to in future model development.

      • yangyingchuan, yeqian, weiying, chenxueshun, chenhuansheng, wangzifa

        Available online:October 09, 2021  DOI: 10.3878/j.issn.1006-9895.2107.21049

        Abstract:Using WRF and IAP-AACM developed by Institute of Atmospheric Physic, Chinese Academy of Sciences, several typical pollution episodes of fine particulate matter (PM2.5) over Hohhot-Baotou-Ordos area of Inner Mongolia in winter of 2016 were analyzed. The resultes indicated that the air quality changes in Hohhot-Baotou-Ordos area were mainly affected by the large-scale synoptic pattern. In the stage of pollution accumulation, at 500 hPa, this area was controlled by the flat westerly airflow in front of the blocking high pressure or weak high pressure ridge; at the ground, this area was located in the weak high pressure or uniform pressure field. The low wind speed and the low height of boundary layer were unfavaorable for the dispersion of pollutants, meanwhile, the air temperature and relative humidity were high, which was conductive to the formation of secondary particles. In the stage of pollution dissipation, the synoptic patterns had significantly changed. Below the 550 hPa, there was strong cold advection, causing the gale weather on the ground, which were beneficial for the elimination of pollutants. Accompanied by cold air moving southward, pollutants over downstream areas were also removed. Local emission was the main source of PM2.5 over Hohhot-Baotou-Ordos area. The contribution of local emission to Ordos was more than 60%, and Hohhot more than 80%, Baotou more than 90%. The change of air quality in this region could reflect the change of regional air pollution meteorological conditions. Cross correlation analysis showed that the PM2.5 concentrations in Shanxi, Hebei and Henan regions were correlated with that in Hohhot-Baotou-Ordos (P < 0.0001) with a phase difference of 6-24 hours. The improvement of PM2.5 pollution in Hohhot-Baotou-Ordos depended on the control of local source emissions. In winter, the air quality change in this region can be used as a precursor factor for the air quality change in the downstream region, which is helpful for the prediction and early warning of air quality in the downstream region.

      • liuyujia, manwenmin, zhoutianjun, pengdongdong

        Available online:October 09, 2021  DOI: 10.3878/j.issn.1006-9895.2109.21119

        Abstract:Stable isotopes in atmospheric water vapor, which can track moisture sources and water vapor transport, are widely used as an important tracer of present-day water cycle. ‘‘Amount effect” is invoked to interpret water vapor stable isotopes at mid-low latitude monsoon region. However, recent studies have shown that non-local factors such as moisture sources and water vapor transport have significant influence on the stable isotopes. Therefore, based on Lagrangian Particle Dispersion Model and Satellite remote sensing δD in water vapor, the main factors affecting water vapor δD are analyzed in the region with abundant Chinese stalagmite δ18O records. On the seasonal scale, water vapor δD is more depleted in late summer and early autumn and enriched in winter and spring. We find this characteristic cannot interpret by "temperature effect" or "amount effect". On the contrary, accumulated rainfall over water vapor transport paths is the dominant factor of water vapor δD and there is a significant negative correlation between them. On the interannual scale, water vapor δD is enriched in the summer of El Ni?o year and depleted in the summer of La Ni?a year. The contribution of moisture sources to water vapor δD is small, but the accumulated rainfall over water vapor transport paths increases significantly in La Ni?a year compared with El Ni?o year. This suggests that tropical convection and depletion in water vapor transport paths are strong in La Ni?a year, resulting in depleted water vapor δD in the study area. In conclusion, upstream convection, measured by accumulated rainfall, is the primary driver of water vapor δD variations on seasonal to interannual scale. Enhanced convection will deplete δD in the study area, while the weakened convection is the opposite.

      • ZHENG Tianxue, TAN Yongbo, LUO Linjie

        Available online:October 09, 2021  DOI: 10.3878/j.issn.1006-9895.2109.21079

        Abstract:In this study, a stochastic lightning parameterization scheme is coupled into the dipole charge structure, and the parameters and positions of the main negative charge region are fixed. Positive intracloud flashes (+IC) initiating at different altitudes are simulated by adjusting the parameters (charge concentration and horizontal range) of the upper positive charge region, and then the relationships between the characteristics of +IC flashes and the distributions of thunderstorm charge are discussed. Simulation results indicate that under dipole charge structures, the elevation of the upper positive charge region can generate high-altitude +IC flashes consistent with observations. Different from normal IC flashes dominated by upward negative leaders and horizontal or slightly downward positive leaders, IC flashes initiated at high altitudes are characterized by long-distance downward positive leaders and horizontal or slightly upward negative leaders. With the elevation of the upper positive charge region, the initiation altitudes of +IC flashes increases. When the upper positive charge region is lifted to a certain altitude (in this paper, the lower boundary altitude of the upper positive charge region is 12 km), IC flashes are usually initiated from the main positive charge region, and the concentration and horizontal radius of the upper positive charge area have no significant effect on the initiation altitude of IC flashes. In addition, the length of positive or negative leader channels has a significant positive correlation with the concentration, horizontal radius of the charge region, and the distance between the initiation point and the negative or positive charge region.

      • zhuchuandong, renrongcai

        Available online:October 09, 2021  DOI: 10.3878/j.issn.1006-9895.2106.21075

        Abstract:The South Asian high (SAH) center is characterized by bimodality distribution (i.e., Tibetan Plateau (TP) mode and Iranian Plateau (IP) mode), showing an east-west oscillation pattern. In addition, east edge of the SAH also regularly extends eastward to East Asia or retreats westward to the TP, manifesting another type of east-west oscillation. By using NCEP1 daily reanalysis data, APHRODITE daily precipitation data and daily precipitation data in India, this paper investigates the relationship between the two types of east-west oscillation of the SAH, and the differences in their impacts on the circulation and weather in Asia. The results show that bimodality east-west oscillation of the SAH center can significantly affect the occurrence and amplitude of eastward extension/westward retreat of the east edge of the SAH. Although the east edge of the SAH can extends eastward when the SAH center is in the TP or IP mode, the frequency of eastward extension of the east edge of the SAH in the TP mode is significantly higher than that in the IP mode; In the IP mode, east edge of the SAH is more prone to retreat westward. And magnitude of eastward extension of the east edge of the SAH in the TP mode is larger than that in the IP mode. Further analysis reveals that bimodality east-west oscillation of the SAH center is closely related to the rainfall anomaly pattern in the northern India and the TP region, and is coupled with the variation of thermodynamic effect related to rainfall anomaly. While the eastward extension/westward retreat of the east edge of the SAH is related to the dipole rainfall anomaly pattern in East Asia (i.e., rainfall anomaly in the central and eastern TP, and in the middle and lower reaches of the Yangtze River and Yellow river, is opposite to that in the region south of the Yangtze river), by resulting in the westward extension/eastward retreat of the western Pacific subtropical high. Furthermore, when the SAH is in the TP mode and its east edge extends eastward, and when the SAH is in the IP mode and its east edge retreats westward, rainfall anomaly in the western TP is always opposite to that in the central and eastern TP.

      • QianXiaoli, QinZhengkun, 张文君

        Available online:October 09, 2021  DOI: 10.3878/j.issn.1006-9895.2105.21063

        Abstract:Based on the multi-year brightness temperature observation data of the AMSU-A (Advanced Microwave Sounding Unit-A) on the polar-orbiting satellite NOAA-15, a product of cloud liquid water path on the global ocean has been established and compared with ERA5 and FNL/NCEP. We analyzed the ability of retrieval products to reproduce the climate change characteristics of cloud liquid water path, and further analyzed the linear and nonlinear climate change trend characteristics of cloud water path in the Pacific region through linear regression and EEMD (Ensemble Empirical Mode Decomposition) methods. The results show that the CLWP inversion data can well reproduce the average spatial distribution characteristics of the years and the corresponding climate change trend. The CLWP climate trend shows obvious latitude zone characteristics, and the increasing and decreasing trends appear with the latitude zone interval. Moreover, in the eastern Pacific region of the northern hemisphere, the latitude zone characteristic of the climatic trend of the CLWP has a phenomenon of migration northward. In contrast, the climatic trend of the inversion product has better similarity with the ERA5 reanalysis data. While the latitude zone characteristics of the trend, especially the northward movement of the latitude zone characteristics, cannot be reproduced well by the FNL data. It is characterized by a decrease in water vapor in the equatorial region, and a significant increase in cloud liquid water paths on both sides.

      • Cui Tong, Zhang Ruonan, Hao Lisheng, Sun Chenghu

        Available online:October 09, 2021  DOI: 10.3878/j.issn.1006-9895.2107.21059

        Abstract:Based on the homogenized daily precipitation in North China and ECMWF-ERA5 reanalysis data for 1961-2018, and a new monitoring standard that takes precipitation and the position of the Western Pacific subtropical high ridge into consideration, we calculated the rainy season precipitation in North China (RSPNC) and onset/ending date with the new monitoring method, and discussed the climatic characteristics of the water-vapor transport and associated interdecadal variations in precipitation and moisture budget. The temporal and spatial variations in water-vapor transport and associated impact on RSPNC were further investigated. The main results can be summarized as follows: (1) The onset/ending dates of the rainy season in North China are distinct in each year, so as the periods of occurrence of the rainy season and the intraseasonal variation. (2) Precipitation is determined by large-scale atmospheric moisture transport and associated convergence. The critical four water-vapor pathways maintained the RSPNC including Indian monsoon, East Asian monsoon, trans-equatorial airflow between 110°E and 120°E, and mid-latitude westerlies near 40°N. (3) The RSPNC and water-vapor budget displays similar interdecadal variations, and abrupt climate changes occurred in 1977, 1987 and 1999, respectively, featuring a "reduction-increase-reduction" phase. The RSPNC is strongly correlated with the net water-vapor budget within the domain of North China. (4) The intensity of water-vapor flux and the arriving timing exert significant impacts on the amount of precipitation. The distribution patterns of water-vapor flux anomalies in rainy decades and rainless decades are distinct: in the rainy decades, the anomalous anticyclonic circulation dominates the Northwest Pacific, and the northward water-vapor transport is strong, which converges with the eastward water-vapor transport over mid-high latitude westerlies in North China, and the water-vapor diverges more strongly than that in normal years. In terms of intraseasonal process, water-vapor fluxes are stronger in amplitude, reach North China earlier, weaken later, converge stronger, and have a longer lifetime. While in the rainless decades, the anomalous cyclonic circulation dominates the Northeastern China, Korean Peninsula, and the area around the Sea of Japan, and it turns into a weaker-than-usual northward water-vapor transport, and the water-vapor divergence is obviously strengthened; accordingly, the intraseasonal process shows the opposite characteristics. (5) Considering the four boundaries of water vapor transport, the southern and weastern boundary water-vapor inputs are the largest and the second-largest, respectively. Their interdecadal variations are critical for the interdecadal variation of the RSPNC. In rainy decades, there are stronger inputs of water-vapor from the southern and western boundary, but strong output from the north boundary; however in rainless decades, water-vapor inputs are weak from the southern and western boundaries, and the output swithes to input from northern boundary, which is essentially distinct from that in the rainy decades.

      • He Linqiang, ZHOU Tianjun, LI Lijuan, LIN Pengfei, CHEN Xiaolong, ZOU Liwei

        Available online:October 09, 2021  DOI: 10.3878/j.issn.1006-9895.2105.21042

        Abstract:In this study, based on observation and JRA55 reanalysis data sets, we systematically evaluate the performance of South Asian Summer Monsoon (SASM) simulated by FGOALS-g3 climate system model. We draw attention to the simulated differences between FGOALS-g3 and FGOALS-g2, coupled model and atmospheric model. Results show that compared with FGOALS-g2, the simulation of climatological Indian Ocean trade winds and the sinking branch of the Walker circulation during El Nin ?o are improved in the FGOALS-g3 owing to the change of local sea surface temperature (SST). However, the systematic cold biases in the middle and upper troposphere persist, causing the reduced meridional temperature gradient and weakened SASM, leading to the biases of descend motion and moisture divergence, and the thus still dry biases over the terrestrial monsoon trough in the FGOALS-g3. Meanwhile, the negative correlation between El Nin ?o—Southern Oscillation and Indian summer rainfall captured by FGOALS-g3 stays weaker than observation, resulting from the weaker descending motion caused by SST biases. Furthermore, results also show that the air-sea interaction-induced climatological SST biases compensate the wet biases in the SASM region via the change of atmospheric circulation and water vapor transportation. At interannual timescale, the inclusion of negative feedback process of SST—precipitation—cloud shortwave radiation in the coupled model effectively improve the biases intensity of rainfall and atmospheric circulation simulated by the atmospheric model; however, the westward biases of sinking branch of the Walker Circulation caused by the SST biases in the coupled model lead to greater wet biases in the Indian Peninsula.

      • GAO Ying, Wang Yu Ying, Li Zhan Qing, Jin Xiao Ai, Wang Jing Ling, Hu Rong, Zeng Si Qi, Zhang Rui, Chen Xi, Xu Jia Lu

        Available online:October 09, 2021  DOI: 10.3878/j.issn.1006-9895.2107.21013

        Abstract:Taking three aerosol field measurement experiments carried out in 2016 summer at Xingtai (XT) site, 2016 winter and 2017 winter at Beijing (BJ) site as examples, typical new particle formation events during these three experiments are selected to analyze their effects on aerosol hygroscopicity and cloud condensation nuclei (CCN) activity. BJ and XT were considered as two typical cities located in a northern megalopolis area and a central-southern industrial area, respectively, in the North China Plain. The formation mechanism of new particles in different seasons at two sites were different, and the corresponding condensation sink (CS), growth rate (GR), and aerosol chemical composition were also different. The dominant chemical species formed during NPF events was organics at BJ site, but which were sulfate and organics at XT site. The further study found that aerosol hygroscopicity and CCN activity were significantly stronger at XT site than those at BJ site, especially for the nucleation mode particles. The above results indicate that the difference in aerosol hygroscopicity and activation ability should be fully considered when estimating the influence of new particle formation on CCN number concentration.

      • SHA Xiu-zhu, HUANG Yi-mei, CHU Rong-hao

        Available online:October 09, 2021  DOI: 10.3878/j.issn.1006-9895.2105.20237

        Abstract:For physical inspection of artificial precipitation enhancement effect based on multi-source detection data,we establish the similarity measurement coefficient APC of contrast area selection,and the dimensionless PIDI index method for physical inspection of artificial precipitation enhancement effect.Results show that:(1)The PIDI index method of physical inspection for artificial precipitation enhancement effect can be used to minimize variability influence of seeding cloud body and precipitation with the similarity coefficient APC,and synthesize a variety of dimensionless cloud physical detection parameters with dimensionless method.Finally,a percentage change rate is used to comprehensively measure the overall variation trend and degree of various cloud physical parameters.(2)The PIDI index method was applied to inspect the precipitation enhancement effect of 24 aircraft from 2014 to 2019.The average change rate of 7 indexes (cloud top temperature,effective particle radius,optical thickness,liquid water path,combined reflectivity,≥30dBZ echo area,vertical cumulative liquid water content) caused by artificial precipitation enhancement was 3.4%~19.6%.The precipitation change rate of 18 operations was 0~58.3%,the precipitation change rate of 6 operations was -37.5%~0.The changes of cloud physical parameters caused by most precipitation-increasing operations are obviously smaller than the changes of precipitation.(3)For the 18 operations with positive effect of precipitation enhancement,cloud top temperature,combined reflectivity and vertical cumulative liquid water content for most operations were increased due to artificial catalysis,effective particle radius,optical thickness and liquid water path for most operations were decreased due to artificial catalysis.(4)The difference and similarity between the PIDI index method and the K-value method were compared by using an aircraft precipitation enhancement operation.For the test of precipitation variation trend,the two are consistent.The difference between the two is that the PIDI index method can reflect the average change rate of all inspection indexes caused by artificial catalysis.

      • LI Yiyu, GUO Xueliang, JIN Lianji, LI Peiren, SUN Hongping, ZHAO Delong, MA Xincheng

        Available online:October 09, 2021  DOI: 10.3878/j.issn.1006-9895.2104.20255

        Abstract:The spatiotemporal distributions of aerosols and their transition to cloud droplets are a key issue in studies of clouds and precipitation and climate change. The properties of vertical distribution, size distribution and origin, as well as their transition relationships with cloud condensation nuclei (CCN) and cloud droplet number concentration are investigated using nine flights of aircraft measurements under clear and cloudy conditions in Shanxi, Central Northern China. Results indicate that the structure of atmospheric boundary inversion layer has an important impact on the vertical distributions of aerosols and CCNs. The size distributions under different weather conditions are similar in the upper atmospheric layers but different at lower levels. The high correlation between aerosols and CCNs can be found in vertical. The linear relation of y=1.3x-616.3 can be found between aerosols and cloud droplets with a determination coefficient of 0.96, and transition rate from aerosols to cloud droplets may reach 47%. The linear relation of y=1.6x-473.8 can be found between CCNs and cloud droplets with a determination coefficient of 0.96, and transition rate from CCNs to cloud droplets may reach 69%.

      • sdsqxjyqj@163.com, Zhang Dianguo

        Available online:September 27, 2021  DOI: 10.3878/j.issn.1006-9895.2107.21043

        Abstract:Based on ground-based micro-rain radar and cloud radar, combined with aircraft observation, a stratiform precipitation with embedded convection is analyzed to study the cloud-precipitation microphysical structure accurately. The results show that: 1) The selected precipitation process is divided into stratified cloud and convective cloud. Above zero layer, especially on the height of 5~6 km, doppler velocity and spectrum width of convective precipitation are greater than that of the stratiform cloud precipitation, which indicates that vertical wind of environment, the size range of the particle occurred in convective precipitation are greater than the stratiform precipitation. 2) At the period of convective precipitation, there is a V-shaped gap caused by attenuation in radar reflectivity of cloud radar and micro rain radar in time and height profiles. The attenuation of cloud radar is grater than that of micro rain radar, the higher the height, the greater the attenuation. 3) At the period of stratiform precipitation, near the bright band,the?leap?increase height of radar reflectivity factor is 80m higher than the Doppler velocity, and the leap?increase height of Doppler velocity is 20m higher than the spectral width. 4) The precipitation mechanism near the zero degree layer of is complex. When the negative temperature is close to 0℃, the particle shape includes aggregated dendritic ice crystals, needle ice crystals and cloud droplets. The Doppler velocity and spectral width of convective cloud precipitation are greater than that of stratiform precipitation above the zero degree layer, especially at the altitude of 5 and 6km. The vertical airflow and the scale range of small and large particles in convective precipitation are greater than that of stratiform cloud precipitation.

      • hujiahui, luchuhan, JIANG Youshan, HeJing

        Available online:September 09, 2021  DOI: 10.3878/j.issn.1006-9895.2104.20225

        Abstract:In recent years, deep learning models has been increasingly used in solving nowcasting problems that have a large impact on disaster prevention and mitigation. In this paper, we took nowcasting as a spatio-temporal sequence prediction task, and use radar reflectivity factor as the test object. We use TAGAN deep learning model based on GAN frame to predict the radar echo image of the future 1h, and compared it with Rover optical flow Method and 3DUnet model based on convolutional neural network. The radar echo data set of the 2018 Global Weather AI Challenge is selected for training and testing. The test results show that the TAGAN model shows advances by multiple scores such as the hit rate (POD), false alarm rate (FAR), critical success index (CSI), and correlation coefficient. The TAGAN model performs well in the above test scores and increases with the prediction time compared to the traditional optical flow method and the comparative deep learning model. Compared with the traditional optical flow model, the improvement effect is more significant. The results may shed some light on expanding and improving the application of deep learning models in near-weather forecasting.

      • 唐兆康, 鲍艳松, 顾英杰, 范水勇, 齐亚杰

        Available online:September 09, 2021  DOI: 10.3878/j.issn.1006-9895.2107.20222

        Abstract:A large number of observations assimilated can effectively improve the results of model forecast. However, there are significant differences in the effects of different observations on the forecast. It is one of the most challenging diagnostics in numerical models to reasonably evaluate the contribution of observations to the forecast. In this paper, the WRFDA-FSO system is constructed by the method of adjoint-based forecast sensitivity to observation(FSO). Based on the wind profile radar detection(WPRD) and ground-based microwave radiometer(MWR) data obtained by the mega city project in Beijing in September 2019, the experiments on the impact of observations on the 12h forecast of WRF model are carried out by using WRFDA-FSO system, and the contribution of wind, temperature and humidity observations to the forecast is analyzed. The results show that: (1) In general, the observations(MWR, WPRD, Sound, Synop and Geoamv) assimilated all reduce the 12h forecast error of WRF model, and make positive contribution to the forecast. Among them, MWR observations have the greatest impact on the forecast, and the improvement of WPRD observations on forecast is better than that of wind field observations of Sound. (2) Among the U and V observations of WPRD and temperature and Specific humidity observations of MWR, the positive contribution value of V observations and temperature observations to the forecast is higher, and the effect of improving the forecast is better. (3)The observations of WPRD and MWR at most levels reduce the forecast error and are positive contribution to forecast, and the positive contribution of temperature observations is mainly below 800 hPa near the ground.

      • ZHOU Xiaoyu, WANG Yongwei, SUN Jihua, YANG Dahu

        Available online:August 27, 2021  DOI: 10.3878/j.issn.1006-9895.2105.21062

        Abstract:In this paper, the coupling Noah/Single Layer Urban Canopy scheme coupled with WRF (V3.9.1) model is used as a control case to study the effects of land use type (Md04 scheme), land surface process (NoUCM scheme) and lake (Nolake scheme) on the intensity of urban heat island and the horizontal and vertical spatial distribution characteristics of urban meteorological elements in Kunming. The main conclusions are as follows: (1) The average daily variation of urban heat island intensity in four cases is basically the same. The UHI intensity is weak in the daytime and strong at night, and reaches the maximum at about 2000 BT. In the case of Control-NoUCM (Nolake), the average daily maximum difference is -0.79oc (+1.07oc). (2) From the energy balance equation analysis of Control-Md04 case, the difference of sensible heat (latent heat) energy is +46.18 (-79.71) w/m2,and the release of latent energy is greater than the absolute value of sensible energy. In the case of Control-NoUCM,the difference of sensible heat (latent heat) energy is -40.88 (+29.60) w/m2. NoUCM scheme does not consider the heat storage and shielding of geometric buildings, and most of them are absorbed by the surface, resulting in a large absolute value of sensible heat flux. (3) In the four cases, the boundary layer height reaches the maximum (minimum) value at 1500(0700) BT. The height of urban boundary layer in NoUCM (Nolake) decreased by about 103m (32m), while that in Md04 case increased by about 102m. (4) The experimental results of the influence of lakes on the circulation of urban heat island show that the vertical movement over the lake is weak, while the horizontal lake land wind is strong, which is conducive to the transportation of water vapor to the city, increasing the humidity of dry air and making the water vapor content higher, thus increasing the release of latent heat energy, reducing the sensible heat flux and reducing the temperature gradient.

      • CHANG Rui, ZHU Rong, ZHAO Dajun

        Available online:August 27, 2021  DOI: 10.3878/j.issn.1006-9895.2108.21071

        Abstract:Based on the in-situ gradient observations from the wind profile radars, WindCubeV2 and masts during the landfall of Typhoon Minguk (1822) and Lekima (1909), combined with the simulated winds of typhoon Minguk (1822) with a finest horizontal resolution of 2 km and vertical resolution of 50-model levels, in which the lower levels are densified, the strong wind structure in the lower level (below 300 m height over sea level or terrain) were analyzed. It showed that within the range of 0-200 km from the typhoon center, (1) the maximum wind speed height and the wind shear index increased outward along the radial direction, and the wind shear index on the land underling surface was generally higher than 0.12. Because of the weak drag effect on the ocean underling surface, the wind shear index was usually small with the exception of island areas; (2) the strong wind shear on the right front quadrant of the moving direction of typhoon remained stable at about 0.17, which was not sensitive to distance and altitude. There existed the wind profile similar to the jet stream on the left rear quadrant, and previous study pointed out that the changes of super-gradient/ sub-gradient wind in the vertical direction should be responsible for the jet type profiles (Tan et al., 2013). The vertical variations of the strong winds on the left front quadrant showed nonlinear characteristics, indicating the more complex strong wind structure over this area; (3) the gust factor and turbulence intensity decreased with the mean wind speed and altitude; (4) the maximum wind direction variation during the landfall of typhoon decreased outward along the radial direction, and exhibited statistically significant spatial asymmetry with the largest variation near the right rear quadrant. Over some areas of the right rear quadrant, the wind direction changed more than 30° in half an hour, and most of them occurred before or during the typhoon"s landfall. It was hoped that these information could be helpful for microscale wind simulation as well as the prevention and mitigation of typhoon disasters over offshore wind farms in China.

      • Jingya Wu, Qiang Sun, Yongheng Bi, Yufang Tian, Yinan Wang, Daren Lyu

        Available online:June 21, 2021  DOI: 10.3878/j.issn.1006-9895.2106.21061

        Abstract:The diurnal variation of cloud macro parameters over the Tibetan Plateau is affected by the combined effects of large-scale circulation, local solar radiation and surface processes, and has an important influence on the radiation budget, transmission of radiation and the distribution of sensible and latent heat. Due to the lack of continuous quantitative observation means, the understanding of the diurnal variation characteristics of cloud macro parameters in various weather systems is still very insufficient. Ka-band cloud radar of APSOS (Atmospheric Profiling Synthetic Observation System) is the first radar to realize long-term cloud observation in the Tibetan Plateau. In this paper, data of APSOS Ka-band cloud radar in 2019 are used to study the time-domain and frequency-domain diurnal variation characteristics of cloud frequency, single-layer cloud top height, cloud bottom height and cloud thickness under the influence of westerly trough, shear line and vortex system. Main conclusions are as follows: (1) The daily mean cloud frequency is 56.9% for the westerly trough system, 50.8% for the shear line system and 73% for the vortex system; (2) Although the genesis of westerly trough and shear line system is different, the diurnal variation trend and main harmonic period of cloud macro parameters of the two systems are similar: the diurnal variation trend is sinusoidal, the minimum value appears before sunrise and the maximum value appears before sunset. The main harmonics of cloud frequency are diurnal (24 hours) and semidiurnal (12 hours) harmonics, and the diurnal harmonics have the largest amplitude among the main harmonics of cloud top height, cloud bottom height and cloud thickness; (3) The diurnal variation characteristics of cloud macro parameters in vortex system is different from that in the first two systems. The diurnal variation of cloud parameters in the vortex system is multi-peak type. Although the harmonic amplitude of diurnal period is the largest among the main harmonics of cloud frequency, single layer cloud top height and cloud bottom height, the spectrum distribution is discrete, and the maximum harmonic period of cloud thickness amplitude is 4.8 hours; (4) The statistical regression equations of diurnal variation of cloud frequency, single layer cloud top height, cloud bottom height and cloud thickness are given.

      • lixiang, Yangshuai, Yangshuyun

        Available online:June 10, 2021  DOI: 10.3878/j.issn.1006-9895.2106.21072

        Abstract:Based on observation analyses and numerical simulation, we reveal that three vortexes, north Plateau Vortex (PLV1), south Plateau Vortex (PLV2), Southwest Vortex (SWV), develop successively during the disaster-causing rainstorm event in Southwest China from 5 to 6 August 2019, which lead to the intensification and eastward propagation of the rainstorm. By utilizing of numerical experiments, the effects of multi-scale topographic factors (Tibetan Plateau, Hengduan Cordillera and Sichuan Basin, denoted as TP, HC and SB) on the evolution of vortexes are studied. The results show that, HC plays a key role in the formation of the SWV, while SB influences the location and intensity of SWV. As for the propagation of Plateau vortex (PLV2 herein), SB only affects the vortex intensity, but does not change the propagation path of PLV2. Once HC is removed, the propagation of the Plateau Vortex disappears. The influence of slope change of the steep terrain at the boundary between TP and SB on the development of vortex is further analyzed. It shows that the steeper the slope is, the faster the propagation speed of the Plateau vortex is, and the stronger the SWV is after the two vortexes (PLV2 and SWV) merge. Finally, the impact of varied slopes on the evolution of vortex intensity is explained based on the theory of slantwise vorticity development. As the slope becomes steeper, the coefficient of slantwise vorticity development (CD) decreases sharply. In the case of steep slope, the forcing effect of rapidly-decreasing CD along the track of vortex glide on the local tendency of vertical vorticity contributes to the rapid intensification of the vortex.

      • Liu Weiguo, Shi Yueqin, Dang Juan, Tao Yue, Zhou Yuquan

        Available online:February 21, 2022  DOI: 10.3878/j.issn.1006-9895.2202.21077

        Abstract:Effect evaluation is still a difficult issue in the weather modification field. Numerical models can play a greater role in the effect evaluation of cloud seeding. Developing numerical models with some more realistic simulation of cloud seeding process is a workable way. In this paper, a three-dimensional mesoscale seeding model has been improved through coupling a new AgI (silver iodide) nucleation calculation scheme. Artificial ice crystal predictand and its associated microphysical processes have been introduced into the model, and the realistic seeding operation modes of both ground-based rockets and artillery have can be simulated by the model. The artificial rainfall reduction operation of a convective cloud system in North China on September 1, 2019, was simulated using the above seeding model with a horizontal grid spacing of 500m. The seeding effect of rainfall reduction operation was evaluated, and the nucleation characteristics and working mechanism of AgI agents in convective clouds were analyzed. The results showed the following: 1) Cloud seeding had some impact on the radar echo intensity of the target cloud system. More precipitation particles stayed in the upper cloud region because of the cloud seeding operation, which slightly increased the echo intensity of the upper part of the cloud body and weakened the echo intensity of the middle and lower part of the cloud body. However, the natural evolution tendency of radar echoes of the target cloud system has not been changed by cloud seeding. 2) Cloud seeding achieved certain rainfall-reducing effects. A large-area rainfall-reducing zone appeared downstream of the operation area. The total rainfall amount was decreased, and the rainfall intensity was weakened. The greatest local value of rainfall amount reduction was 0.27mm, and the rainfall in the main affected area decreased by 5.1% on average. 3) Condensation-freezing nucleation was the main nucleation mode of the AgI agent, followed by contact-freezing nucleation mode. 4) Cloud seeding operation caused an overseeding effect. The growth of artificial ice crystals was in a dominant position during competition, and the natural growth processes of other hydrometeors in the supercooling cloud area were suppressed. The deposition growth of artificial ice crystals was the main reason for the increase in depletion of water vapor and cloud water, and deposition latent heat release eventually led to the change of vertical airflow velocity in the cloud. 5) The cold cloud precipitation process was the main physical mechanism of the rainfall. Due to the influence of cloud seeding, the weakening of the graupel melting process (Mgr) in the warm layer led to the decrease of the total mass of raindrops, which was the main reason for the weakening of rainfall, while the decrease in the number of raindrops falling into the lower part of the warm layer was another reason for the weakening of rainfall.

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      • Fu Conghin, Wang Qiang

        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.

      • 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.

      • HAN Zhenyu, ZHOU Tianjun

        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.

      • 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。

      • 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.

      • 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.

      • 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.

      • 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.

      • 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.

      • 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。

      • 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。

      • Jin Zuhui, Tao Shiyan

        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。

      • 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.

      • 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.

      • 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.

      • 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。

      • Liu Shida, Zhang Ziguo

        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。

      • BAO Qing, Bin WANG, LIU Yimin, et al

        2008,32(5):997-1005, DOI: 10.3878/j.issn.1006-9895.2008.05.01

        Abstract:East Asian monsoon precipitation and circulation have experienced an interdecadal change in the last 50 years that was concurrent with the changes in global SST and recent global warming. What gives rise to this long term change has been an outstanding issue. One possible cause is the change over the Tibetan Plateau. To understand the possible impact of the Tibetan Plateau surface conditions on the downstream East Asian monsoon, a suite of sensitivity experiments were performed with Hamburgs atmospheric general circulation model (ECHAM). The land surface albedo was changed in two sets of sensitivity tests so that the Tibetan Plateau land surface temperature was changed accordingly.  The results show that a warmer condition over the Tibetan Plateau tends to enhance the upper tropospheric South Asia high and the westerly jet stream to its north and the Indian monsoon to its south, meanwhile the moisture transport toward East Asia increases. The changes in the precipitation pattern are featured by increasing rainfall over northwestern India and Meiyu and decreasing rainfall in the regions under the control of Pacific subtropical high and the Bay of Bengal.  Preliminary diagnostic analysis suggests that the plateau warming has initially increased sensible heating and convective heating locally, which then enhanced the low-level southwest monsoon transport toward down stream of the plateau, resulting in increased precipitation and latent heat release in eastern China. The changes in the overall diabatic heating strengthen the upper-tropospheric South Asia high and downstream subtropical trough. This result may have meaningful implications for understanding the interdecadal change and future change of the East Asian summer monsoon.

      • ZHANG Jie, ZHOU Tianjun, YU Rucong, et al

        2009,33(1):121-134, DOI: 10.3878/j.issn.1006-9895.2009.01.11

        Abstract:The atmospheric water vapor transports associated with typical anomalous spring rainfall patterns have been investigated using NCEP/NCAR, ERA40 monthly mean reanalysis data and precipitation data of 160 stations in China during 1951-1999. Results show that origins of water vapor supply related to anomalous rainfall patterns are different from the climate mean situation. In anomalous pattern 1, with a heavier rainbelt along the South China coast, the main moisture comes from the Philippine Sea and the adjacent South China Sea. The background large-scale circulation changes include the intensification of the western Pacific subtropical high (WPSH) and the southwest shift of the East Asian jet stream (EAJS). In anomalous pattern 2, with a main rainbelt along the middle and lower reaches of the Yangtze River, the origins of water vapor supply contain the western tropical Pacific and the tropical Indian Ocean. Both the WPSH and the EAJS move to the north of their normal position. In anomalous pattern 3, a rainy region is located in the Huaihe River valley. The moisture originates from the northwestern Pacific. The 500-hPa anticyclone anomaly moves to northeastern China and the EAJS is weaker than its normal condition. Although water vapor transport along the southern edge of the Tibetan Plateau is one of the main branches in the climate mean pattern, none of the typical water vapor transport related to typical anomalous rainfall reflects this water vapor flow.


    主办单位:中国科学院大气物理研究所
    ParentUnit:中国科学院
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