Volume 44,2020 Issue 5

• Numerical Simulation Study on the Microphysical Characteristics of Stratiform Clouds with Embedded Convections in Northern China based on Aircraft Measurements

  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(937) HTML(1839) PDF(7.18 M)( 2160)

  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.

• The Causes of Low Predictive Skills of Precipitation in Flood Season in Northeast China

  ZHAO Junhu, XIONG Kaiguo, CHEN Lijuan

  2020,44(5):913-934, DOI: 10.3878/j.issn.1006-9895.1911.19132

  Abstract(841) HTML(3118) PDF(22.71 M)( 1677)

  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.

• Numerical Investigation of the Effects of Boundary Layer Parameterization Schemes on Typhoon Meranti (1614) Landing Process

  WANG Yehong, ZHAO Yuchun

  2020,44(5):935-959, DOI: 10.3878/j.issn.1006-9895.2004.19135

  Abstract(673) HTML(2098) PDF(10.98 M)( 1556)

  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.

• Contribution of Tropical and Subtropical Circulation Anomalies to the Intensity of East Asian Winter Monsoon over Lower-Latitude Region

  PENG Jingbei, LIU Ge, SUN Shuqing, HE Kejun

  2020,44(5):960-974, DOI: 10.3878/j.issn.1006-9895.1911.19141

  Abstract(682) HTML(2471) PDF(6.84 M)( 1765)

  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.

• A Vertical Second-Order Difference Scheme for Non-uniformly Distributed Layers and Its Application in GRAPES Model

  XU Daosheng, CHEN Dehui

  2020,44(5):975-983, DOI: 10.3878/j.issn.1006-9895.1906.19145

  Abstract(594) HTML(1672) PDF(2.67 M)( 1507)

  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.

• Influence of Stochastically Perturbed Parameterization on Ensemble Forecasting of Winter Precipitation in China

  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(652) HTML(1506) PDF(4.90 M)( 1852)

  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.

• Spatial Observation of Red Sprites over a Winter Mesoscale Convective System in North America and the Analysis of Its Parent Thunderstorm

  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(677) HTML(2168) PDF(8.55 M)( 1580)

  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.

• Correction for Cirrus Cloud Top Height of MODIS Based on CALIPSO Dataset in the Beijing–Tianjin–Hebei Region

  YANG Bingyun, LIU Jian, JIA Xu

  2020,44(5):1013-1022, DOI: 10.3878/j.issn.1006-9895.1911.19181

  Abstract(742) HTML(3524) PDF(3.41 M)( 1492)

  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.

• The Properties of Convective Generating Cells Embedded in the Stratiform Cloud on Basis of Airborne Ka-Band Precipitation Cloud Radar and Droplet Measurement Technologies

  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(822) HTML(2693) PDF(4.16 M)( 1777)

  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.

• Advances in Atmospheric Predictability of Heavy Rain and Severe Convection

  MIN Jinzhong, WU Naigeng

  2020,44(5):1039-1056, DOI: 10.3878/j.issn.1006-9895.2003.19186

  Abstract(778) HTML(2574) PDF(3.46 M)( 1820)

  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.

• Contrasting Salinity Interannual Variations in the Tropical Pacific and Their Effects on Recent El Niño Events: 1997/1998, 2014/2015, and 2015/2016

  SHI Shiwei, ZHI Hai, LIN Pengfei, CHEN Tao

  2020,44(5):1057-1075, DOI: 10.3878/j.issn.1006-9895.1912.19172

  Abstract(743) HTML(2651) PDF(6.18 M)( 1736)

  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.

• Experiments on Simulation of Typhoon Soudelor with GRAPES Hybrid-3DVar System

  ZHUANG Zhaorong, LI Xingliang, CHEN Jing, SUN Jian

  2020,44(5):1076-1092, DOI: 10.3878/j.issn.1006-9895.1911.19193

  Abstract(730) HTML(1685) PDF(46.23 M)( 1405)

  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.

• Numerical Simulation of the Effect of Urbanization on a Single Extreme-High-Temperature Event in Beijing

  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(601) HTML(1803) PDF(6.53 M)( 1752)

  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 (I_UHI) 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 I_UHI 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.

• The Causes of Variation in the Zonal Asymmetry of the Asian Westerly Jet and Its Impacts on East Asian Climate in Boreal Summer

  ZI Ran, KONG Zhen, ZHANG Qiyue, XIA Yang

  2020,44(5):1109-1124, DOI: 10.3878/j.issn.1006-9895.2005.19232

  Abstract(786) HTML(4558) PDF(7.36 M)( 1557)

  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 (I_Aja) 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.

• Interdecadal Variation Characteristics of Extreme Low Temperature Index in Winter in China

  Suolang Tajie, SHI Ning, WANG Yicheng, ZHANG Dongdong

  2020,44(5):1125-1140, DOI: 10.3878/j.issn.1006-9895.2003.19242

  Abstract(727) HTML(4080) PDF(10.00 M)( 1643)

  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.

• Evaluation of Simulated Tropical Cyclones over the Western North Pacific with IAP AGCM4.1 Based on K-Means Method

  ZHOU Ying, ZHANG He, ZHANG Kewei

  2020,44(5):1141-1154, DOI: 10.3878/j.issn.1006-9895.2002.19252

  Abstract(583) HTML(1924) PDF(7.96 M)( 1677)

  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.

Online First

• Analysis of the Characteristics of low-level mesovortex during a record-breaking wind event in North China Plane

  xuchangyi, Zhang Lina, Xiao Xian

  Available online:April 29, 2025  DOI: 10.3878/j.issn.1006-9895.2504.24124

  Abstract(0) HTML(0) PDF(4.83 M)( 0)

  Abstract:On June 25, 2020, Tianjin Xiqing was affected by a convective storm accompanied by a mesovortex (MV), which produced record-breaking gust (41.4 m?s-1) since the observation started in 1957. In order to improve the scientific understanding of extreme thunderstorm winds caused by such mesoscale vortex, the thermodynamic structure characteristics and maintenance mechanism of MV were analyzed by using the Variational Doppler Radar Analysis System (VDRAS) technique of radar data combined with multi-source observation data. The results show that the MV in this process was initially born at a height of 2.0 km, and the contracting and stretching vertical vortex rapidly descended to surface from 2.0 km height with the rotation speed increasing and vortex diameter contracting. During this process, the surface transition from warm and dry to cold and wet cyclonic vortex, extreme wind appeared in the overlap area of western of MV and rear inflow jet (RIJ). The evolution of MV was closely related to the different properties in convective storms. In the mature stage of MV, the vertical circulation was formed by tilt updraft (TUD), RIJ, front flank downdraft (FFD) and forward low-level inflow (FLI). During the strengthening and descent of MV, the rainwater evaporated and absorbed heat during its descent, leading to a significant enhancement in the intensity of RIJ and its continuous downward extension. The configuration of the cold pool and vertical wind shear plays crucial role in the evolution of MV: from the formation to development stage of MV, the cold pool and low-level vertical wind shear from 0-3 km height reach a stage of equilibrium; from the development to mature stage of MV, the cold pool and bulk vertical wind shear from 0-6 km height reach a balanced stage; from the mature to dissipation stage, the intensity of cold pool exceeds the bulk vertical wind shear, which is unfavorable for the storm development. Distinct from the ground-reaching RIJ associated with typical bow echo, the RIJ in this event did not reach the ground, but instead coupled with the vertical downdraft of MV in near an altitude of 1 km, generating a vertically downward perturbation pressure gradient force. Meanwhile, the drag effect of rainwater facilitated the strengthening of the downdraft. During its descent, evaporation and heat absorption weakened the cold pool, which in turn intensified the surface wind speed, collectively leading to the extreme gale.

• A Short Review about the Influence of Aerosols on Cloud and Precipitation

  Chuanfeng Zhao, Jiefeng Li, Yikun Yang

  Available online:April 01, 2025  DOI: 10.3878/j.issn.1006-9895.2503.25015

  Abstract(10) HTML(0) PDF(1.52 M)( 14)

  Abstract:Aerosols mainly influence cloud formation and precipitation by regulating the radiative energy balance and altering cloud droplet properties through aerosol-cloud interactions. This paper provides a comprehensive review of the microphysical effects of aerosols. As cloud condensation nuclei or ice nuclei, aerosols can significantly alter the radiative and microphysical characteristics of clouds. An increase in aerosol concentration can lead to smaller cloud droplet sizes, increasing the cloud albedo to shortwave radiation, referred to cloud albedo effect. Simultaneously, aerosols can enhance the longwave radiation emitted by thiner clouds, blocking more longwave radiation in atmosphere, which is known as the cloud thermal emissivity effect. However, absorbing aerosols may promote cloud droplet evaporation, thus reducing the cloud albedo. Ferthermore, aerosols have significant impact on precipitation. When water vapor is insufficient or wind shear is strong, an increase in cloud droplet and a reduction in droplet effective radius can suppress precipitation and extend the cloud"s lifetime. However, when clouds develop more deeply, more and smaller droplets can be transported above the 0°C level, where freezing releases latent heat, promoting convective rainfall. Therefore, the microphysical effects of aerosols can suppress weak precipitation and enhance strong precipitation, leading to an increase in extreme weather events. However, many studies have observed phenomena that are inconsistent with these theories. To explain these discrepancies, this paper systematically presents four physical mechanisms behind aerosol-cloud interactions: condensation and evaporation effects, water vapor competition effects, collision and coalescence effects, and entrainment effects. The competition among these mechanisms leads to the varied results observed in studies. Finally, the paper discusses the challenges and future research directions, with an emphasis on enhancing observational data capabilities, developing a comprehensive framework for aerosol-cloud interactions under varying conditions, optimizing parameterization schemes, and advancing the application of artificial intelligence.

• Analysis on the Causes of the Extreme Winds on March 31, 2024, in Nanchang, Jiangxi Province

  Li Shufan, Wang Xiuming

  Available online:March 18, 2025  DOI: 10.3878/j.issn.1006-9895.2503.24089

  Abstract(50) HTML(0) PDF(6.66 M)( 40)

  Abstract:Extreme winds disaster occurred in Nanchang, Jiangxi Province in early morning on March 31, 2024, which is responsible for the fall of three residents from a high building. Based on SA dual-polarization Doppler weather radar observations from Nanchang and surface observations, this study analyzed the fine structure of the severe storm near the accident building. The results revealed that a bookend vortex was embedded in the northern end of the bow echo within a quasi-linear convective system around the time of the accident, with its horizontal scale and vertical vorticity comparable to that of a strong mesocyclone. Tornado vortex signatures (TVS) with tornado debris signatures (TDS) were identified in the center of the bookend vortex which passed over the accident building. The rotational velocity of the TVS exceeded 40 m·s-1. Damage surveys conducted along the tornado path identified by TVS and TDS revealed multiple tornadic damages, including strong cyclonic rotational winds, localized convergent rotational winds, debarked trees and complete collapse of stone bridges. This indicated that an EF2 tornado occurred very close to the accident building, most likely responsible for the fatal fall. It is noteworthy that the tornado-related vortices include a bookend vortex and several leading-edge misocyclones embedded within it, which emerged and intensified almost simultaneously in this event. The observational study on the formation mechanisms indicated that those tornado-related vortices resulted from the tilting of the horizontal vorticity. The horizontal vorticity is associated with the strong low-level vertical shear of the elevated rear-inflow jet and the baroclinic vorticity related to the gust front.

• Characteristics and influencing factors of planetary boundary layer height variation in Tengchong

  金莉莉

  Available online:March 11, 2025  DOI: 10.3878/j.issn.1006-9895.2502.24135

  Abstract(52) HTML(0) PDF(2.23 M)( 39)

  Abstract:Tengchong is located in the Yunnan-Guizhou Plateau with complex terrain and is a typical mountain city. The planetary boundary layer (PBL) and its cross-border transport of pollutants caused by its special geographical location urgently need attention, so it is of great significance to study the long-term boundary layer structure and the changing characteristics of meteorological conditions in Tengchong. In this paper, the L-band radiosonde data of Tengchong and the atmospheric boundary layer height (PBLH) calculated by Richardson number method are used to verify the ERA5 reanalysis data. Based on the ERA5 reanalysis data, the temporal characteristics and influencing factors of PBLH in Tengchong during 1980-2023 are analyzed by statistical method. The results indicate that the PBLH of ERA5 has a good correlation with the observed PBLH in Tengchong, and the average PBLH of ERA5 is 3.7m and 279.4m lower than the observed PBLH at 08:00 and 20:00, respectively.The PBLH in Tengchong showed significant fluctuations, with an upward trend in summer and autumn (0.7 m/yr, 0.2 m/yr), a downward trend in spring and winter (-0.1 m/yr, -0.2 m/yr), and an upward trend in dry and wet seasons (0.05 m/yr, 0.3 m/yr). PBLH was the order in spring (1504m) > winter (871m) > Autumn (572m) > summer (468m) at daytime, while at night, PBLH was the order in summer (52m) > Autumn (23m) > Spring (27m) > Winter (19m). PBLH in wet season (44m) was higher than that in dry season (21m). PBLH fluctuates greatly during the daytime and is relatively stable at night, reaching the daily peak at 14:00 or 15:00 in the afternoon. The PBLH can exceed 3500m in dry season and 2000m in wet season. The daily PBLH fluctuates the most in spring and dry season. On the annual scale, PBLH was positively correlated with 10m wind speed, surface sensible heat flux, ground-air temperature difference, surface temperature and 2m air temperature, and negatively correlated with relative humidity, total cloud cover, surface latent heat flux and 2m dew point temperature. On the seasonal scale, the PBLH in spring, autumn, winter and dry season was mainly driven by 10m wind speed, while in summer and wet season it was mainly driven by high latent heat flux, total cloud cover, relative humidity and low sensible heat flux. In the diurnal variation, 10m wind speed, surface sensible heat flux and relative humidity in daytime were the main factors affecting the development of PBLH, while the surface latent heat flux at night was the only significant factor affecting the development of PBLH.

• Influence of direct assimilation of FY-3D satellite MWHS II data on July 31 rainstorm forecast in Beijing

  徐忠燕, duhan, pingfan

  Available online:March 11, 2025  DOI: 10.3878/j.issn.1006-9895.2501.24107

  Abstract(28) HTML(0) PDF(3.75 M)( 37)

  Abstract:This study examines the impact of direct assimilation of FY-3D satellite MWHS II microwave humidity sounder data on the prediction of extreme rainfall, using the July 31, 2023, heavy rainstorm in Beijing as a case study. Comparative experiments were conducted before and after data assimilation, and the WRF numerical prediction model was applied to analyze the effects across multiple scales and variables. The results show that the assimilation of MWHS II data significantly improved the simulation of extreme rainfall. It successfully captured the maximum rainfall center, exceeding 550 mm, and provided a more accurate simulation of rainfall distribution. The study also highlights the effect of assimilation on large-scale systems. It improved the large-scale environmental field, creating conditions that favored the extreme rainfall event. Key improvements included a strengthened temperature gradient in critical areas, optimized water vapor distribution, especially over the eastern sea, and an increased north-south pressure gradient. Together, these factors maintained a stable large-scale background that supported precipitation. On a smaller scale, the impact on convective systems was even more noticeable. Over the Beijing area, the vertical vorticity structure was optimized, with enhanced negative vorticity in the mid-to-upper atmosphere and increased positive vorticity in the lower levels, which promoted upward motion. The atmosphere became more unstable, with increased relative humidity in the lower levels, decreased humidity in the mid-levels, and a steeper vertical temperature gradient. These factors contributed to the triggering and maintenance of strong convection. Additionally, the microphysical processes were improved. More snow and graupel particles formed in the mid-to-upper layers, and the conversion of cloud water to rainwater accelerated in the lower levels, enhancing the overall precipitation efficiency. These effects were most prominent during the first 36 hours of the simulation, emphasizing the critical role of data assimilation during the early and developing stages of precipitation.

• A Parameterization Scheme for Westerly Wind Bursts in the Western Tropical Pacific Based on the U-Net Model and its Relationship with ENSO

  ZHOU Yusheng, ZHI Hai, ZHANG Rong-hua, DU Shuangying

  Available online:March 06, 2025  DOI: 10.3878/j.issn.1006-9895.2501.24080

  Abstract(26) HTML(0) PDF(695.49 K)( 87)

  Abstract:El Ni?o-Southern Oscillation (ENSO) is the strongest interannual climate mode in the atmosphere-ocean coupling system over the tropical Pacific. Westerly wind bursts (WWBs) are an important precursor of the ENSO events. In the past few decades, several statistical and dynamics-based models have been used to simulate and predict ENSO events. However, these models have some difficulties in simulating WWBs, leading their simulation and prediction performance for ENSO events that are also limited. This study constructs U-Net models that are driven by several atmospheric and oceanic data for zonal wind anomalies (ua) in the tropical Pacific. Furthermore, the spatiotemporal characteristics of WWBs are identified and their relationship with ENSO phenomenon are analyzed. The results indicate that the U-Net model can effectively simulate the spatiotemporal distribution characteristics of WWBs during the testing period (2003-2022). The deviation between the occurrence frequency and accumulated days of WWBs reconstructed by the model and the observed values is less than 4.0 %, and the correlation coefficient between the time series of WWBs occurrence probability (P) simulated by the model and observed values 0.87. Meanwhile, the U-Net model can effectively capture the non-linear relationship between WWBs and ENSO, and there is a significant lead-lag correlation between WWBs and ENSO in both U-Net models and reanalysis data. Besides, the duration, zonal width and the average maximum amplitude of WWBs reach their peak during El Ni?o events, and the peak of probability (P) of WWBs during El Ni?o events reconstructed by the U-Net model is much closer to that of observation. In conclusion, compared with the traditional WWBs parameterization scheme that relies on establishing an approximate linear relationship between WWBs and sea surface temperature fields, the U-Net model has significant advantages in representing WWBs.

• Examining Upper-Level Aviation Turbulence over China and its Surroundings based on a combination of multi-source observations

  Wang Sixian, SHOU YIXUAN, Liu Haiwen, Lu Feng

  Available online:March 06, 2025  DOI: 10.3878/j.issn.1006-9895.2411.24070

  Abstract(64) HTML(0) PDF(2.61 M)( 46)

  Abstract:Upper-level aviation turbulence is triggered by turbulence in the free atmosphere. It is a major concern for aircraft operations. Under a warming climate, the turbulence over China shows a trend of increasing. To better understand the sources and characteristics of the upper-level aviation turbulence over China, two sets of Aircraft Meteorological Data Relay (AMDAR) are used to establish a one-year global turbulence observation dataset in the form of eddy dissipation rate (EDR) through quality controls and consistency processing. Based on the aviation, FY-4A satellite observations and the ERA5 reanalysis, the spatial distribution, as well as the seasonal and diurnal variations of three types of upper-level aviation turbulence, clear-air turbulence (CAT), near-cloud turbulence (NCT), and convective-induced turbulence (CIT) over China, are analyzed. It is found that the active zone of the clear-air turbulence is prone to occur in the upper troposphere near the tropopause in the vertical direction. Near-cloud turbulence over China has 4 active zones, which are located in eastern, northern China, and the South Sea, as well as over Japan. The northern to eastern slopes of the Qinghai Tibet Plateau are regions with a high probability of near-cloud turbulence in western China. The convective-induced turbulence concentrated more over southern China. All three types of turbulence exhibit typical seasonal and diurnal variations. Clear-air turbulence is more common in the afternoon during winter and spring seasons, while near-cloud and convective-induced turbulence are more likely to occur in the morning during summertime.

• Asymmetric Characteristics and Maintenance Mechanisms of the East Asian Winter Temperature Anomaly Reversal Mode

  Li Qiao, Liu Boqi

  Available online:March 06, 2025  DOI: 10.3878/j.issn.1006-9895.2501.24041

  Abstract(39) HTML(0) PDF(9.53 M)( 42)

  Abstract:The reversal of temperature anomalies from warm to cold and vice versa in the East Asian region is one of the most significant climatic phenomena during the winter season under the context of global warming. Compared to the variability of seasonal-mean winter temperature anomalies, the climate prediction uncertainty for the reversal phenomenon is greater, and its adverse impacts are more significant. Based on atmospheric reanalysis data from the winters of 1980/81 to 2022/23, this study employs seasonal empirical orthogonal decomposition and composite analysis methods to investigate the interannual variability of the East Asian winter temperature anomaly reversal mode (TARM). The results indicate that although the different processes of the East Asian winter TARM are related to intraseasonal reversals of the Siberian High, the Eurasian teleconnection and the Arctic vortex anomalies, the interannual variability of the "warm to cold" mode is significantly stronger than that of the "cold to warm" mode, suggesting a pronounced asymmetry in the interannual variability of TARM. In the "warm to cold" mode, the lower-level Siberian High strengthens over time, with the positive phase of East Atlantic-West Russia-like teleconnection in early winter shifting to a negative phase in late winter, leading to more active cold air. Conversely, in the "cold to warm" mode, the intensity of the winter Arctic vortex shifts from weak to strong, the Siberian High weakens after that, favoring the appearance of temperature anomalies that are cold in early winter and warm in late winter. Further analysis shows that North Atlantic and tropical Indian Ocean sea surface temperature anomalies with La Ni?a are important factors influencing the "warm to cold" mode, while a reduction in November Barents-Kara sea ice acts as a precursor signal for the "cold to warm" mode. Therefore, the diversity of atmospheric underlying conditions is an important reason for the asymmetry of the East Asian winter TARM. Therefore, climate prediction for the East Asian winter TARM should consider the diversity of atmospheric underlying conditions.

• Further Simulation and Analysis of the Triple-frequency Radar in Detecting Cloud

  HUOJUAN

  Available online:March 06, 2025  DOI: 10.3878/j.issn.1006-9895.2407.24038

  Abstract(35) HTML(0) PDF(691.73 K)( 42)

  Abstract:Based on our prior research, this paper carries out the simulation of three typical short-wavelength radar detections (X-band-9.5GHz-3cm, Ka-band-35GHz-8mm, and W-band-94GHz-3mm) for non-precipitation cloud particles, particularly ice crystals. It further compares and analyzes the radar reflectivities stemming from variations in the particles" physical attributes. Additionally, the study explores the feasibility of employing these three radar wavelengths to discern the morphology of ice crystals. The results show that, despite the W-band"s short wavelength and heightened sensitivity, the backscattering characteristics of ice crystals exhibit a considerably more intricate pattern than those observed in the X-band and Ka-band. Variations in incident angle, particle morphology, and particle size elicit dramatic and complex alterations in backscattering, posing a formidable challenge to traditional inversion methods that rely on statistical or empirical fitting approaches to extract cloud particle microphysical properties. It has also been shown that utilizing the characteristics of the differences between multi-wavelength radar observations can help to provide microphysical information about particles in clouds. For example, in the ice cloud, a pronounced disparity in reflectivity factor between the W-band and either the Ka-band or X-band, particularly when it dips below -3 dBZ, suggests the likelihood of prolate particle presence. This offers invaluable insights and practical experience for refining and enhancing the accuracy of algorithms designed to invert cloud microphysical features based on triple-frequency radar data.

• Environmental Conditions and Evolutionary Characteristics of the Tornadic Storms in Liaoning Province on June 1 2023

  Yang Lei, Zheng Yongguang

  Available online:March 06, 2025  DOI: 10.3878/j.issn.1006-9895.2410.24027

  Abstract(72) HTML(0) PDF(2.53 M)( 43)

  Abstract:Based on multi-source observations and ERA5 reanalysis data, we present in detail the environment conditions, storm evolution and possible formation mechanisms of the Fuxin EF1 tornado and the Kaiyuan EF2 tornado on June 1 2023 in this paper. The results show that the northern part of Liaoning Province was affected by the upper trough and lower-level shear line at the rear part of a Northeast China Cold Vortex. The strong vertical temperature lapse rate between the surface (or 850 hPa) and 500 hPa was the extreme environmental condition factor that caused this process. The Fuxin tornado storm had hook echo, descending reflectivity core (DRC) and tornado vortex signature (TVS), formed by the merger of two isolated storms generated on the dry-line. The strong echo on the east side of tornado storm generated the strong cold pool with the surface temperature dropped by more than 6 ℃ within one hour. The outflow of cold pool merged with the dry-line, forming a triple point at the edge or the strong cold pool. When the hook echo moved to the triple point, a moderately strong downdraft produced a cold pool with suitable intensity, coupled with the strong convergence and uplift at the triple point, the tornado generated under the DRC and TVS. The Kaiyuan tornado storm was a linear convective system, formed by the merger of multiple storms along the surface convergence line. Due to Kaiyuan"s location within the low-level jet and its stronger low-level wind shear, it was conducive to the initial formation of a misocyclone on the ground convergence line. The cold pool with a temperature dropped by more than 10°C within an hour was produced by the storm at the west side of the misocyclone. The cold pool outflow merged with the surface convergence line to form a triple point, resulting in stronger convergence in Kaiyuan than that of Fuxin. When the misocyclone passed through the triple point, under the strong convergence and stretching effect, the low-level rotation of misocyclone reached its strongest in the life cycle which first met the TVS standard and the Kaiyuan tornado generated. The Northeast cold vortex process had extreme conditions of instability, the storms generated on the dry-line and surface convergence line, produced a strong cold pool within an area of about 30 km near the tornado genesis zone. At the edge of the strong cold pool where the ground temperature dropped less than 4°C within an hour, the humidity conditions of the lower atmosphere were improved. The triple point was also formed to strengthen the ground convergence. When the TVS or the misocyclone passed through these triple confluence points, tornadoes were formed respectively.

• Evaluation of cloud detection method for FY-3D/HIRAS based on CALIPSO data

  tianshaolong, Xiao Xianjun, Xu Zhongyan, Pingfan

  Available online:March 05, 2025  DOI: 10.3878/j.issn.1006-9895.2407.24057

  Abstract(21) HTML(0) PDF(1.26 M)( 39)

  Abstract:Cloud detection is a critical step in the application of infrared high-spectral radiance observations, directly impacting the effectiveness of satellite data utilization. McNally proposed a method in 2003 based on observed and simulated brightness temperature differences for channel cloud detection, widely applied in satellite data quality control for numerical weather forecasting. Building upon McNally's method, this study utilizes Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) cloud classification data products to quantitatively assess the cloud detection performance of FY-3D High Spectral Infrared Atmospheric Sounder (HIRAS), using precision and recall as validation metrics. This enhances the quality and assimilated data volume of FY-3D HIRAS products. Results show: (1) The precision of FY-3D HIRAS channel cloud detection is 97.19%, with a recall of 93.74%, and the Root Mean Square (RMS) error of O-B (observed brightness temperature minus background brightness temperature) caused by false clear-sky channels (cloud channels detected as clear-sky) is 0.984 K, generally within observational error variance in numerical forecasting. This confirms the method does not compromise data quality and can effectively apply to numerical weather forecasting. (2) According to CALIPSO's analysis of different cloud types, stratocumulus (St), stratocumulus (Sc), and fractured cumulus (Cu fra) exhibit high precision but lower recall. Altocumulus (Ac), altostratus (As), and deep convective clouds (DC) demonstrate high precision and recall. Cirrus (Ci) shows lower precision but higher recall.

• Analysis of potential mechanism of extreme low temperature in South China during the spring of 2022

  Lu Chuying, Qi Li

  Available online:March 05, 2025  DOI: 10.3878/j.issn.1006-9895.2501.24075

  Abstract(62) HTML(0) PDF(7.76 M)( 56)

  Abstract:Extreme low temperature events often lead to significant impacts on residents" lives and crop growth. Therefore, it is important to analyze the causes of extreme low temperature events. Based on the temperature observation data of CN05.1 and reanalysis data of ERA5 during the period of 1980-2022, this study focuses on the spatial and temporal distribution characteristics of the extreme low temperature event that occurred in the South China in May 2022 and reveals the circulation background and possible factors affecting this event. The analysis reveals that the intensity of this extremely low temperature event is strong, the temperature is lower than 3 standard deviations compared with the average state of May 1980-2022. Besides, the cold lasted as long as 31 days and affected more than 1.5 million square kilometers. Therefore, it was the strongest extreme low temperature event since 1980. Further analysis shows that there was a significant wave train in the middle troposphere over the middle and high latitudes of Eurasia, and also an anomalous low pressure over South China, which made the cold air in the middle and high latitudes move deep south. At the same time, the re-intensified La Ni?a in the equatorial Middle East Pacific made the convective suppression center more westerly and stronger, and the related Rossby wave formed an anomalous anticyclone in the east of the Philippines. Then the southerly wind on the west side of this anticyclone transported warm and humid air from the ocean to South China, converged with the cold air to generate convection which significantly reduced the surface net shortwave radiation and made the temperature lower. Therefore, the extremely low temperature event in South China in May 2022 is the result of the joint action of the circulation related to cold air activity and the Philippine anticyclone. Using these two factors to construct the fitting equation, the reproduced temperature can reach -2 standard deviation.

• The Biogeophysical Impact of Different Land Use Changes on Near-Surface Air Temperature in China under the SSP1-2.6 "Double Carbon" Pathway

  WEI Miao, SUI Yue, LIU Bo

  Available online:March 04, 2025  DOI: 10.3878/j.issn.1006-9895.2412.24030

  Abstract(38) HTML(0) PDF(2.82 M)( 42)

  Abstract:In the past century, changes in land use and land cover have affected climate change mainly through biogeochemical and biogeophysical processes, and the biogeophysical effects on air temperature in China are still uncertainty. Thus, this study utilizes data of six models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to project the biogeophysical influence of different land use and land covers (i.e., under SSP3-7.0 and SSP1-2.6) on temperature in China during the "double carbon" period under Shared Socioeconomic Pathway (SSP) SSP1-2.6, and quantitatively analyzes the factors involved. Results indicate that: (1) During the "double carbon" period under SSP1-2.6, the difference of land use and land covers under two scenarios is that forest cover increases in the south of the Qinling-Huaihe River regions and decreases in the north, with greater differences in the carbon-neutral period (?10% to 10%) than in the carbon peak period (?8% to 5%). Differences in forest cover in western China are minimal. (2) National mean, its contribution to future warming during the carbon peak period is ?5%, and it is greater than that during the carbon-neutral period (?1%). (3) This contribution also exhibits regional disparities. In north eastern China, there is a transition from a negative contribution during the carbon peak period (?3.2%) to a positive contribution during the carbon-neutral period (0.4%). This is attributed to the combined results of increased warming effects of ground heat fluxes, clear-sky longwave radiation, and sensible heat fluxes, as well as enhanced cooling effects of surface albedo and latent heat fluxes. South eastern China exhibits negative contributions (?4.1% and ?1.8%) throughout the “double carbon” period, resulting from the cooling effects of cloud radiation and the enhanced warming effects of ground heat fluxes, clear-sky longwave radiation, and sensible heat fluxes. In western China, the positive contribution during the carbon peak period (4.9%) shifts to a negative contribution during the carbon-neutral period (?1.8%), primarily due to the transition of warming effects from ground heat fluxes and clear-sky radiation to cooling effects. Overall, the results suggest that forest cover in the ssp126-ssp370Lu experiment generally has a cooling effect during the "double carbon" period under SSP1-2.6, partially mitigating the impacts of greenhouse gases; however, regional disparities exist.

• Effects of Aerosols on Lightning Activity in Regions with Different Lightning Diurnal Variations

  WANG Haichao, TAN Yongbo, SHI Zheng, ZHENG Tianxue

  Available online:March 04, 2025  DOI: 10.3878/j.issn.1006-9895.2412.24048

  Abstract(46) HTML(0) PDF(1.67 M)( 46)

  Abstract:This study investigated the relationship between lightning activity and aerosols in the Sichuan Basin (region 1) and Guangdong region (region 2) by analyzing 9-year (2010-2018) summer datasets of cloud-to-ground (CG) lightning and aerosol optical depth (AOD) data. The results indicate that there is a non-linear relationship between AOD and CG lightning flashes in regions 1 and 2, with thresholds of~0.5 and~0.3 for AOD, respectively. When AOD is below the threshold, the CG lightning flashes in both regions increases with the increase of AOD. When AOD exceeds the thresholds, the relationship between the CG lightning flashes and AOD becomes scattered in both regions. However, in Region 1, the CG lightning flashes still increases overall with the increase of AOD, while in Region 2, the CG lightning flashes initially shows no significant change and then decreases with the increase of AOD. The relationship between lightning activity and aerosols in regions 1 and 2 is determined by the relationship between lightning and aerosols that occur at night and in the afternoon, respectively. Combined with the radiation suppression effect of aerosols, it is stronger during the day and weaker at night, which may lead to different relationships between lightning activity and aerosols in the two regions under conditions with high aerosol content. In addition, the diurnal variation of CG lightning flashes in regions 1 and 2 shows bimodal and unimodal forms under various aerosol loading, respectively. Under condition with high aerosol loading, the peak in the evening of region 1 and the peak in the afternoon of region 2 appear later.

• Carbon budget assessment of lakeside farmland ecosystem in Erhai Lake

  PENG Juan, XU Anlun, LI Yu, YANG Cheng, ZHANG Guotao, DU Qun

  Available online:March 04, 2025  DOI: 10.3878/j.issn.1006-9895.2409.24072

  Abstract(35) HTML(0) PDF(2.59 M)( 41)

  Abstract:A long-term observation (2007-2012) of CO2 fluxes during the rice and broad bean growing seasons was conducted in the Erhai Lake riparian farmland ecosystem using eddy covariance techniques. The study clarified the characteristics of CO2 flux changes and the source/sink function of the farmland ecosystem under the condition of crop rotation of the two crops. The results showed that: (1) The climatic conditions of the lakeside farmland in Erhai Lake are quite different when rice and broad bean are different underlying surfaces. In the rice growing season, the temperature (Ta) and relative humidity (RH) were relatively high, the saturated water vapor pressure difference (VPD) showed a trend of first decreasing and then stabilizing, the total solar radiation (Rg) fluctuated significantly, and the wind speed (WS) and friction velocity (ustar) showed a weak downward trend. In the growing season of broad bean, Ta showed a trend of first decreasing and then increasing, RH showed a gradual decrease, while VPD and Rg showed an upward trend, and WS and ustar showed a trend of first increasing and then decreasing. (2) The CO2 fluxes in the Erhai Lake riparian farmland ecosystem showed obvious diurnal and seasonal variation characteristics, showing a "U"-shaped diurnal variation pattern and a single-peak double-trough "W"-shaped seasonal variation pattern. During the rice growing season, the peak of CO2 fluxes occurred during the jointing and heading stages; during the broad bean growing season, the peak of CO2 fluxes occurred from podding to seed filling. (3) On the daily scale, the main controlling factor for the change of CO2 fluxes in the Erhai Lake riparian farmland ecosystem was RH, while on the hourly scale, it was Rg. (4) The rice-broad bean farmland ecosystem generally showed carbon sink characteristics. The net carbon exchange during the rice growing season was 503.8 gC.m^-2, and the gross primary productivity was 866.6 gC.m^-2; the net carbon exchange during the broad bean growing season was 143.5 gC.m^-2, and the gross primary productivity was 716.2 gC.m^-2. The carbon sequestration capacity of the rice growing season was about 3.5 times that of the broad bean growing season.

• Influence of Quasi-biweekly Oscillation on Monsoon Trough Rainstorm in summer in Guangdong province

  JI Zhongping, GU Dejun, YU Lingling, Gao Xiaorong, Han Pucheng, Liang Weijie

  Available online:March 04, 2025  DOI: 10.3878/j.issn.1006-9895.2412.22138

  Abstract(32) HTML(0) PDF(8.61 M)( 35)

  Abstract:Using NCEP/NCAR daily reanalysis dataset and Guangdong daily precipitation from 1961 to 2017, by selecting and classifying the rainstorm processes in the warm sector in Guangdong only caused by South China Sea monsoon trough without the frontal system, the temporal and spatial distribution characteristics of different types of monsoon trough rainstorm processes and their relationship with atmospheric low-frequency oscillations are studied, focusing on revealing atmospheric circulation field evolution characteristics in phase of quasi-biweekly oscillations and the sources of low-frequency signals with strong southwest monsoon jet-type monsoon trough rainstorm process, by the methods of synthetic analysis, wavelet analysis and Lanczos filter. The strong southwest monsoon jet type monsoon trough rainstorm process accounted for 53.1% of the total cases, mainly occurring in the three major rainstorm centers (Yangjiang-Yangchun-Enping, Haifeng-Lufeng-shanwei, Longmen-Fogang) along the coast and inland of Guangdong. The other three types of monsoon troughs rainstorm process (strong southwest monsoon convergence type, southeast monsoon disturbance type, tropical cyclone away type) mainly occurred in the two major rainstorm centers along the coast of Guangdong and on both sides of the Pearl River Estuary. The monsoon trough rainstorm process mainly exhibit quasi weekly (5-8 days) and quasi biweekly (10-28 days) oscillations but less 32-65 days oscillations. During the intermittent-start-peak-weak period of strong southwest monsoon jet-type monsoon trough rainstorm process，the low-frequency signal not only originates from the southeastward-propagatian of the quasi-barotropic low-frequency wave train consisting of a series of anomalous anticyclones and cyclones from Western Europe to Northeast Asia，but also originates from the northwestward propagation of low-frequency cyclones in the tropical western Pacific of southeast Philippines in the middle and lower troposphere. They made the South Asian High move westward from Bangladesh to Pakistan, the western Pacific subtropical high gradually strengthened and extended northwestward, from Balkashi Lake to Baikal lake ,central and eastern China is controlled by low frequency anticyclonic circulation or high pressure ridge in intermittent period gradually turning into low frequency cyclonic circulation or upper trough in peak period. In South China, the upper-air divergence gradually increases and reaches the strongest, as the strong northeasterly at the southeast side of the low-frequency anticyclonic circulation gradually changes to the strong westerly from the bottom of low-frequency cyclonic circulation which controls the North China and South of the Yangtze, and the northwesterly from periphery of low-frequency anticyclone which controls the Indian Peninsula-Northwest South China Sea. The middle and lower layers are gradually controlled from the low frequency anticyclone circulation or high pressure ridge to the strong southwesterly which comes from the north of the low frequency anticyclone which controls the central and northern South China Sea and the Bay of Bengal, the strong low-frequency cyclonic circulation and positive vorticity are formed over Southwest China, South of the Yangtze and South China ,when the strong southwesterly are blocked by the low-frequency anticyclone circulation over Northeast Asia, Japan and the southwestern Pacific. The Sea level pressure gradually changed from a weak uniform pressure filed to a closed low pressure extending northwards from the Beibu Gulf , the South China Sea monsoon trough lifts northward and strengthens, making the strong southwest monsoon jet-type monsoon trough rainstorm from the intermittent to peak period. These are beneficial to medium-extended-range forecast of monsoon trough rainstorm processes.

• Decomposition of Tropical Atmospheric Circulations Based on Velocity Potential and Their Responses to Global Mean Sea Level Rise

  WU Mingna

  Available online:March 04, 2025  DOI: 10.3878/j.issn.1006-9895.2502.24082

  Abstract(40) HTML(0) PDF(2.37 M)( 38)

  Abstract:The global mean sea level (GMSL) has risen by 0.16 meters over the past century, which has caused various climate challenges on both global and regional scales. Tropical atmospheric circulations are direct drivers of weather and climate anomalies, playing critical roles in determining global heat and moisture exchange. Understanding the influence of GMSL rise on tropical atmospheric circulations can help improve climate change adaptation and mitigation efforts. Here, using climate model simulations based on the Norwegian Earth System Model (NorESM1-F), we decompose the upper tropospheric velocity potential into Hadley circulation-, Pacific Walker circulation-, and monsoon circulation-related components. We then investigate changes in the Hadley circulation, Pacific Walker circulation, and monsoon circulation in response to GMSL rise under different GMSL rise scenarios. The results show that the velocity potential decomposition method effectively captures the climatology and seasonal evolutions of tropical atmospheric circulations. We further find that, in response to GMSL rise, the Hadley circulation weakens in both the Northern Hemisphere (NH) and Southern Hemisphere (SH) during the boreal summer and the SH Hadley circulation strengthens during the boreal winter. The Pacific Walker circulation shows a slight strengthening and exhibits a shift towards the east and both the East Asian winter and summer monsoons strengthen along with the rising GMSL.

• Evaluation of the Applicability of Satellite-Derived Precipitation in Monitoring Extreme Precipitation in North China

  chenshuang, chentao

  Available online:March 04, 2025  DOI: 10.3878/j.issn.1006-9895.2412.24085

  Abstract(16) HTML(0) PDF(3.63 M)( 38)

  Abstract:Strengthening the monitoring and analysis of extreme precipitation is crucial for early warning of disaster weather. Based on daily precipitation data from the national basic stations of China Meteorological Administration from 2000 to 2023, the applicability of three near-real-time daily products of GPM for monitoring extreme precipitation in North China during summer is analyzed from the perspectives of extreme precipitation indices and extreme heavy precipitation events. The results indicate that: 1) IMERG products tend to overestimate precipitation, particularly in the Shandong Peninsula, with IMERG_V6L showing a more pronounced overestimation, in contrast, GSMAP_GNRT6 tends to underestimate precipitation, especially in the foothill regions.2)Precipitation amount and intensity indices generally exhibit higher correlations in the transitional regions between mountains and plains compared to other areas, while precipitation duration and heavy precipitation frequency indices show relatively lower correlations in these regions, and in regions with more precipitation, the correlations are higher than in regions with less precipitation.3) satellite-derived precipitation can capture extreme precipitation days, with IMERG_V6L performing the best, however, the absolute intensity of precipitation is generally significantly underestimated. Using relative thresholds such as percentiles and TOP values can reflect the spatial distribution of extreme precipitation, but there is an issue of overestimation in the spatial extent, with GSMAP_GNRT6 showing the most pronounced overestimation.Overall, IMERG and GSMAP have potential for application in monitoring and analyzing extreme precipitation in North China during summer, but different products should be distinguished and applied according to different regions and application scenarios.。

• An Intraseasonal Evolution Perspective on the Long-term Trend of Summer Air Temperature over the Eastern Tibetan Plateau

  duojiciren, shining

  Available online:March 04, 2025  DOI: 10.3878/j.issn.1006-9895.2502.24088

  Abstract(50) HTML(0) PDF(1.66 M)( 43)

  Abstract:In summer, the air temperature on the Tibetan Plateau (referred to as the "Plateau") has the intraseasonal variation characterized by initial warming followed by cooling. Therefore, studying the long-term changes in intraseasonal air temperature will help to deepen the understanding of the long-term air temperature change on the Plateau. Based on the JRA55 and ERA5 reanalysis datasets, this paper analyzes the long-term warming trend of summer air temperatures in the eastern Tibetan plateau from the perspective of intraseasonal evolution, as well as its atmospheric thermodynamic mechanisms. The results show that the warming trend of the summer temperature in the eastern Tibetan plateau is mainly related to three factors: (1) the significantly accelerated warming rate in mid- and late June; (2) the significantly decelerated cooling rate in mid-August; (3) the significantly prolonged duration of the warming period. Thermodynamic diagnostic results indicate that the meridional temperature advection, which climatologically acts as a cooling role, shows a long-term weakening trend, which may be an important cause of the warming of summer temperatures in the eastern Tibetan plateau. It should be noted that while both reanalysis datasets generally reveal the consistent evolution of air temperature over the eastern Tibetan plateau, there are certain differences in descripting the thermodynamic budget equation, with the JRA55 dataset seemingly revealing better diagnostic results.

• Study on the Effects of Turbulent Coherent Structures and Flux Additional Term on the Diurnal Surface Energy Balance

  ZHAO Jianhua, ZHANG Qiang, LIANG Yun, Long Xiao, Han Hui, Niu Lijun

  Available online:February 28, 2025  DOI: 10.3878/j.issn.1006-9895.2501.24074

  Abstract(39) HTML(0) PDF(1.40 M)( 40)

  Abstract:The deficiency of the eddy covariance method is an important cause of surface energy imbalance. This article conducts research on the large eddy average method and Durand method proposed in the literature to overcome the deficiency of eddy current correlation method and achieve surface energy balance. The similarities and differences, comprehensive effects, and improvement methods of the two methods were studied through five groups of test during the daytime. The results showed that: (1) The closure level of surface energy is related to the length of the sequence; (2) the original Energy Balance Ratio (EBR) was 0.80, and the Energy Residual (Res) was 64.9W m-2^{; (}3) After considering the large eddy averaging method, the EBR increased to 0.98 and the Res decreased to 14.5W m-2^{, reaching a} balance; (4) After considering the Durand method, the EBR increased to 0.95 and the Res decreased to 25.1W m^-2, which was less effective than the large eddy average method; (5) After considering both the large eddy averaging method and the Durand method, the EBR increased to 1.17 and the Res decreased to -35.1W m^-2, resulting in severe over closure. Analysis reveals that the cause of severe over closure is due to the Durand method"s excessive accumulation of gas expansion and work done; (6) When not considering the sensible heat additional term of the Durand method, only considering its latent heat additional term, and simultaneously considering the large eddy average method, the result can realize an ideal surface energy closure state, which EBR achieves to 1.0 and Res is reduced to 8.7W m-2^{, only account}ing for 3.2% of the available energy. Analysis shows that the large eddy averaging method is the absolute dominant factor in achieving surface energy closure.

• Application of Microwave Remote Sensing Data in Typhoon Fullness Extraction

  ZHANG Guosheng, Fang He, Sun Yi

  Available online:February 28, 2025  DOI: 10.3878/j.issn.1006-9895.2412.24056

  Abstract(23) HTML(0) PDF(2.27 M)( 52)

  Abstract:Tropical cyclone fullness (TCF) is a dimensionless metric that integrates both the inner- and outer- core scales of a typhoon to characterize the storm wind structures, which shows particular direction significance for operational typhoon forecasting. Spaceborne microwave sensors, which are capable of directly observing typhoon ocean surface winds regardless of weather conditions, offer a new technical approach for the accurate extraction of TCF.Taking super typhoon Mawar (2023) as example, this study proposed a TCF retrieve method by collecting spaceborne Synthetic Aperture Radar (SAR), scatterometers, and radiometers data. Subsequently, we make a comparison between model results and typhoon best-track data. Results show that multi-source spaceborne microwave sensor data has good applicability in TCF estimation. The root mean square error (RMSE) and correlation coefficient between satellite-retrieved and best-track data are 0.07 and correlation coefficient 0.82, respectively. Although the typhoon intensity estimates from spaceborne scatterometers are significantly lower than the reference data, the estimates for the radius of maximum wind (RMW) and the radius of 17 m/s winds (R17) are accurate. Specifically, ASCAT-B measured storm RMW and R17 are 17.9 km and 35.2 km, and ASCAT-C are 18.5 km and 43.8 km for ASCAT-C, respectively. Despite working different frequency bands and having varying spatial resolutions, this study demonstrates that multisource microwave sensors are highly suitable for TCF extraction.

• Comparative evaluation of the lightning location system in Sichuan Province before and after the upgrade

  Tian Ye, Pang Wenjing

  Available online:February 28, 2025  DOI: 10.3878/j.issn.1006-9895.2412.24008

  Abstract(12) HTML(0) PDF(2.65 M)( 37)

  Abstract:This article presents a comparative analysis of the detection performance differences between two types of lightning location systems, namely the newly built DDW1 and the original ADTD in Sichuan Province, based on the 2022 observation data of 78 DDW1 sensors and 19 ADTD sensors. The research findings are as follows: 1. Using an altitude threshold of 1000 m, topography significantly affects lightning detection network configurations: station spacing in mountainous regions varies greatly and lacks uniformity, whereas networks in plains are more compact and evenly distributed. 2. The cloud-to-ground flash positioning results of both the DDW1 and ADTD systems are found to be consistent with radar echoes. 3. With the exception of the Ganzi station, the trigger thresholds of the 16 co-located stations for both systems exhibit consistency. Furthermore, the 15 co-located stations demonstrate high consistency in terms of GPS error amplification factor and noise passing rate. However, there are 5 co-located sites that exhibit inconsistencies in crystal oscillator deviation values. 4. In most areas of Sichuan Province, the cloud-to-ground lightning density of the DDW1 system is approximately twice that of the ADTD system. However, there are still detection limitations for thunderstorms in western Sichuan Province. The positive and negative return stroke current peaks detected by the ADTD system range between 20~30 kA and -30~-20 kA respectively, while the corresponding peak values of the DDW1 system are 10~20 kA and -20~-10 kA respectively. The positive and negative return stroke peak current intensities of the DDW1 system are approximately 1.04 times that of the corresponding ADTD system. 5. Overall, the consistency of the normalized return stroke electric field, north-south peak magnetic field, east-west peak magnetic field and azimuth angle of the DDW1 and ADTD sensors at the same site is poor, while the consistency of the return stroke time and post-zero-crossing time is moderate. 6. The time distribution of cloud-to-ground flash positioning results for both the DDW1 and ADTD systems follows a similar pattern to the time distribution of return strokes detected by stations. They exhibit an approximate bimodal distribution, with peak activity observed during nighttime and a decrease during noon. 7. The capture rates of return strokes for both DDW1 and ADTD stations are found to be suboptimal. In the future, it is recommended to develop propagation time correction algorithms suitable for complex terrains and apply equipment measurement calibration technology to the National Lightning Detection Network (CNLDN). The research findings serve as a scientific basis for the subsequent construction, operation and application of CNLDN’s observation data.

• Short-time Heavy Precipitation Short-term nowcasting Forecast Technology Based on Multi-source data Fusion Integration

  Zhang Haiyan, Wu Qishu, Wei Guofei, Fu Chao

  Available online:February 28, 2025  DOI: 10.3878/j.issn.1006-9895.2501.24061

  Abstract(9) HTML(0) PDF(7.69 M)( 42)

  Abstract:A forecast model of short-time heavy precipitation (greater than 20 mm h-1) for 1–12 h at 1 h intervals in Fujian is established based neighborhood with optimal Threat Score by real-time precipitation observation data from ground weather stations, 0–120 min Quantitative Precipitation Forecast from Sever Weather Automatic Nowcasting (SWAN-QPF) of China Meteorological Administration, and forecast precipitation data from global and regional models from April to September during 2021–2023. Neighborhood test is adopted, and the test radius is 40 km. The results show that the accuracy of nowcast in the couple of hours is greatly improved by using real-time precipitation observation to forecast the short-time heavy precipitation (Persistence forecast) compared with using multi-model optimal weight integration. After the optimal elimination threshold correction, the TS in the future first hour can reach 37.5% for 2021 and 32.2% for 2022 when the forecast precipitation is calculated with 10-min real-time precipitation before the forecast production, the neighborhood radius (Ri) of 0.5°, and the average of the top 5 heavy precipitation stations (Ntop=5) in Ri. And at the second hour, the TS can reach 22.2% for 2021 and 19.5% for 2022. The TS of the consensus forecast combining global and regional models with optimized weights can reach 16.2% for 2021 and 16.6% for 2022 at the first hour (18.0% and 14.2% at the second hour) when the forecast precipitation is calculated with the Ri of 0.6° for each model and Ntop=15. The SWAN-QPF short-time heavy precipitation prediction revised by the optimal elimination threshold (the Ri of 0.3° and Ntop=15) is also better than multi-model optimal weight integration, but less than using real-time observational precipitation in the first couple of hours. For the 3–12 h forecast, multi-model optimal weight integration is better than the other two. The above-mentioned multi-source data revised by the optimal elimination threshold are further integrated with optimized weights in the future 1–4 h, and multi-model optimal weight integration is adopted in the future 5–12 h to establish the forecast model of short-time heavy precipitation for 1–12 h at 1 h intervals. The parameters trained with 2021 and 2022 data are applied to forecast short-time heavy rainfall in Fujian in 2023, and the TS are 42.7%, 28.8%, 23.1% and 20.2% in the future 1–4 h, and all above 17% in the future 5–12 h.

• Synergistic Interannual Evolution of Two Types of El Ni?o and Precipitation over the Middle and Lower Reaches of the Yangtze River

  XuBoyang, Zhang Ronghua, Wu Minmin, Zhi Hai

  Available online:January 23, 2025  DOI: 10.3878/j.issn.1006-9895.2410.24055

  Abstract(28) HTML(0) PDF(2.99 M)( 46)

  Abstract:Based on the signal separating and reconstructing of the Multi Taper Method – Singular Value Decomposition (MTM-SVD) method, this study investigates the impacts of interannual SST forcing associated with the El Ni?o-Southern Oscillation (ENSO) on precipitation over the middle and lower reaches of the Yangtze River Basin (MLYR), as well as possible underlying mechanisms. Our results show the MLYR precipitation is associated with the tropical Pacific SST at two distinct time periods, i.e., the quasi-biennial (2.4-year) and quasi-quadrennial (3.7-year) periods, which is related to the CP-type and EP-type El Ni?o, respectively. These two types of El Ni?o trigger different atmospheric circulation responses in the East Asia, both positively impacting the interannual variability in the precipitation over the MLYR. On the quasi-biennial period, the mature phase of CP-type El Ni?o leads to an East Asian-Pacific atmospheric teleconnection. On the quasi-quadrennial period, the mature phase of EP-type El Ni?o results in a meridional dipole-like distribution of atmospheric activity centers over East Asia. Additionally, both types of El Ni?o events trigger the western North Pacific anomalous anticyclone (WNPAC) during their mature phases. These atmospheric circulation systems collectively enhance the moisture transport from the South China Sea to the MLYR, thereby increasing local precipitation. Furthermore, our case analyses show that there is a difference in the relative contribution of the quasi-biennial and quasi-quadrennial periods to the MLYR precipitation variations in 2002. In the spring of 2002, the quasi-quadrennial period contributes to the increase in precipitation over the MLYR, while the quasi-biennial period weakens it. The opposite situation appears in the autumn of 2002. This study refines our understanding of how the multi-timescale forcing of the tropical Pacific SST affects the interannual variability of MLYR precipitation. Our conclusion can help to improve the accuracy of local precipitation forecasts in the MLYR.

• Characteristics of weak anthropogenic influences on high background ozone concentrations in the desert cities of western China

  zhangshaoting, WuBayi, WangFang, WuHong, RenXinbing, MaYongjing, WuFangkun, SunYang, ZhouXingjun, TianYongli, xinjinyuan

  Available online:January 21, 2025  DOI: 10.3878/j.issn.1006-9895.2412.24005

  Abstract(22) HTML(0) PDF(4.84 M)( 45)

  Abstract:There are large gaps in domestic and international research on the characteristics of ozone(O3) concentration evolution in desert areas. Alxa Left Banner belongs to a typical desert city in the western China, which has high background concentrations of O3 on the basis of low intensity of anthropogenic activities. From 2015 to 2022, the annual growth of the 8-hour moving average of daily maximum ozone (MDA8 O3) was about 2 μg·m-3. And the average MDA8 O3 in spring, summer, autumn and winter was 111.3 μg·m-3, 132.3 μg·m-3, 101.8 μg·m-3 and 82.9 μg·m-3. Due to the favourable conditions of high temperature and strong radiation, the atmospheric photochemical reaction of O3 will be promoted and the secondary production of O3 will be enhanced, thus the O3 pollution incidents mainly appear in the summer. The O3 concentrations in Alashan Left Banner were 93-106 μg·m-3 in the summer night under the influence of NO titration effect, indicating that the Alashan region was controlled by high background O3 level. The higher the distance from the observation site to the ground, the higher the O3 concentration. The observations show that the near-surface anthropogenic emissions has direct and significant influence on the vertical O3 concentrations at three stations with different heights over the ground surface. Setting the O3 concentration at the Huanbaojuxinlou Station (22 m above the ground) as a criteria. The O3 concentration at the Mengeryou Station, which is 15 m above the ground, is lower by 5-25 μg·m-3 during the night, and it is higher by 5 μg·m-3 during the noon; the O3 concentration at the Xihuayuan Station, which is 12 m above ground, is lower by 10-25μg·m-3 during the night, and it is higher by 5 μg·m-3 during the noon. The stronger NO titration effect was found in the near ground atmosphere in the urban area at night. However, the higher O3 was found in the near ground atmosphere due to the convective diffusion and rapid photochemical reaction. The effect of weak human activities on O3 concentration was illustrated, and the vertical distribution characteristics of O3 in desert cities were reflected.

• Mechanisms of Arctic Sea Ice in Autumn Influencing the Varying Annual Cycle of the Stratospheric Polar Vortex

  Yang Yanru, Yu Yueyue, Li Yafei, Wu Yufeng

  Available online:January 21, 2025  DOI: 10.3878/j.issn.1006-9895.2501.24095

  Abstract(20) HTML(0) PDF(2.46 M)( 62)

  Abstract:This paper, based on the ERA5 reanalysis dataset and the NOAA sea ice concentration (SIC) data, accurately extracted the varying annual cycle of the stratospheric polar vortex (SPV) using the Ensemble Empirical Mode Decomposition (EEMD) method. We further identified key sea ice regions associated with the interannual changes in the build-up and break-up date of the SPV, and investigated how autumn sea ice in the key region influences the evolution of SPV through both thermal and dynamic processes. Results show that there are significant interannual variations in both the SPV build-up and break-up dates, with the variation in break-up dates being more pronounced. Years with anomalously late (early) SPV build-up and early (late) break-up tend to have an anomalously strong (weak) SPV in mid-winter. Late SPV build-up is linked to warm temperature anomalies in the polar stratosphere during late winter to early spring, creating favorable conditions for SPV early break-up events. Further investigation shows a positive correlation between October SIC in the Barents Sea and the SPV build-up date, likely due to its influence on planetary wave modulation and reflected shortwave radiation in autumn. However, the statistical significance is relatively low, indicating a limited role of sea ice in the SPV build-up. Conversely, October SIC in the East Siberian Sea shows a significant negative correlation with the SPV break-up date. The primary mechanism behind this relationship is that anomalously low SIC in the East Siberian Sea suppresses the upward propagation of planetary waves. This leads to Eliassen-Palm (E-P) flux divergence anomalies, stronger stratospheric circumpolar westerlies. Thereby, SPV break-up is delayed, which is dominated by slow diabatic processes. In contrast, high SIC enhances planetary wave propagation, resulting in E-P flux convergence, weaker circumpolar westerlies. Therefore, SPV break up earlier, which is due to rapid dynamic processes.

• Spatial and temporal characteristics of rainy seasons along the western edge of the Hengduan Mountain and its possible mechanisms

  LI Zhi, YUAN Weihua

  Available online:January 21, 2025  DOI: 10.3878/j.issn.1006-9895.2411.24081

  Abstract(68) HTML(0) PDF(25.54 M)( 46)

  Abstract:The western edge of the Hengduan Mountain (WHDM) is one of the regions where the rainy season starts the earliest in China and the spring precipitation amount in some stations even surpassing summer precipitation. Using high density station rainfall data and the European Centre for Medium-Range Weather Forecasts fifth generation reanalysis products (ERA5), the detailed range of spring precipitation over the WHDM is analyzed in this paper and the possible causes of regional differences in spring precipitation are discussed. The typical spring precipitation region over the WHDM locates in the Nujiang River Valley in Yunnan province between 26.57°N-27.8°N. In this region, the rainy season starts from the 9th pentad (mid-February). The rainy season can last for over to eight months, with the highest proportion of spring precipitation in the whole year. And the annual precipitation peak occurs before April. The rainy seasons start before April both in the eastern region (E) and the southern region (S), which are adjacent to the region W of spring rain stations. However, annual rainfall there are dominated by summer precipitation. Further analysis shows that the precipitation difference between region E and typical spring rain region W may be affected by the dynamic background difference caused by topography and westerly in early spring, and also by the difference of water vapor condition caused by the difference of southerly in late spring. The difference of precipitation between region S and typical spring rain region W may be mainly affected by the different water vapor conditions caused by the difference of meridional winds, and the difference of vertical uplift motion under the action of local topography may also have an important contribution.

• A Case Study on Machine Learning Correction of Surface Layer Turbulent Fluxes over a Farmland

  LIU Zhenrong, LI Yubin, WANG Hon, LIU Xinye, Gao Zhiqiu

  Available online:January 21, 2025  DOI: 10.3878/j.issn.1006-9895.2501.24077

  Abstract(25) HTML(0) PDF(3.73 M)( 53)

  Abstract:Turbulent fluxes in the surface layer are significant variables that characterize the interaction between the land and the atmosphere, which are typically calculated based on the Monin-Obukhov Similarity Theory (MOST) in gradient observations or atmospheric numerical models. To further enhance the calculational accuracy of turbulent fluxes in the surface layer, in this paper, the turbulent fluxes derived from the MOST are corrected by Random Forest and XGBoost, with fluxes obtained by the eddy covariance method as reference values, which significantly improves the calculational accuracy of the temperature scale and moisture scale. In order to reduce the number of input variables, this study further performs forward and backward variable selection on the input variables The optimal combinations of input variables after selecting still maintain a high level of computational accuracy. Furthermore, when the selected combinations of input variables are applied to another machine learning model, the artificial neural network, their computational accuracy also show a significant improvement in comparison with the results of MOST. This demonstrates that the variable selection method in this paper of input variables required for machine learning method.

• Winter Snowfall Microphysics Characterized by a 2-D Video Disdrometer (2DVD) in Beijing

  luoli, chenyichen, Yutiantian, chenmingxuan, Xiaohui

  Available online:January 21, 2025  DOI: 10.3878/j.issn.1006-9895.2409.24083

  Abstract(23) HTML(0) PDF(3.63 M)( 59)

  Abstract:The study of snow microphysics is important to understand the mechanism of winter precipitation and to optimize the cloud microphysical parametrization scheme in the weather model. However, there are few researches on the microphysical characteristics of snowfall in China at present. In order to thoroughly understand the microphysical characteristics of snowfall in Beijing, the particle size distributions (PSDs), fall velocity (V), snow density(ρ), axis ratio (ar) and their relationship with equivalent diameter of six snowfall events observed by a 2D video disdrometer were investigated in this paper. The results showed the following: (1) The snow density with particle median volume diameter (D0) less than 1.5 mm is smaller than that reported in other regions, and the V(D) relationship is related to the snow density. The fall velocity of snow particles increases with the density and is moderately larger (smaller) than that in Colorado (Nanjing) for a given diameter. (2) The 5-minute PSDs for each case are fit with exponential and normalized gamma distribution models. The concentration intercept (N0 and Nw) and the slope (Λ) parameters for both fitting models present an almost same time series, while the errors between D0, Nt (total number concentration) and SR (snowfall rate) (SR) calculated from gamma PSD and that derived from 2DVD measurements was relatively small. (3) A directer correlation between the Nw and D0 can be observed after considering the effect of density on the Nw-D0 relation. (4) The mean aspect ratio (ar) of the snowflakes is 0.76, and the ar is close to 1 when the diameter is larger than 2.5 mm. (5) For a given SR (Ze), the decrease (increase) of Ze (SR) is accompanied with an increase of ρ and Nw while a decrease in D0. In addition, for a given Ze, the Ze–SR relationship in Nanjing overestimates snowfall rate.

• Possible connection between increased precipitation in May in Jiangnan and accelerated warming of Southern Tropical Indian Ocean sea surface temperature

  GUO Hao-Kang, LI Chun

  Available online:December 25, 2024  DOI: 10.3878/j.issn.1006-9895.2410.24043

  Abstract(28) HTML(0) PDF(2.65 M)( 84)

  Abstract:Based on the fact that the overall trend of precipitation in May in Jiangnan has been upward since 1980, this paper takes the precipitation in May in Jiangnan from 1980 to 2021 as the research object, and uses the data of CPC (Climate Prediction Center) precipitation, NCEP (National Centers for Environmental Prediction) atmospheric circulation, and Hadley center sea surface temperature to analyze the precipitation trend characteristics in May in Jiangnan, diagnose the water vapor budget, and finally discuss the possible physical processes. The results indicate that the dynamic component of precipitation in Jiangnan in May is one order of magnitude larger than the thermal component, and both of them have no obvious trend change from 1980 to 2005, but show significant increase trends from 2006 to 2021. The Southern Tropical Indian Ocean (STIO) sea surface temperature anomaly (SSTA) in May has begun to warm at an accelerated pace since 2001, establishing a significant positive correlation with the Northwest Pacific anomalous anticyclone (WNPAC). Since 2004, the trend of WNAPAC in May has changed from significant weakening to significant strengthening, and in 2005 it has been significantly correlated with the abnormal increase of precipitation in Jiangnan in May, and the warm SSTA of southern tropical India associated with WNAPAC has lasted from February to May. Since 2006, while the WNAPAC has intensified, the anomalous convection over the STIO has developed eastward, and the resulting updraft has sunk over the Philippine Sea, the South China Sea and the Indochina Peninsula with the Hadley Circulation, forming a more pronounced convective dipole structure than in 1980–2005. The downdraft has strengthened the WNPAC, which has promoted the transport of water vapor to Jiangnan, and the thermal component of the anomalous precipitation in Jiangnan in May has increased. After the enhancement of WNPAC, the secondary circulation between the active area of WNPAC and Jiangnan is more compact, the uplift of Jiangnan is enhanced, and the dynamic component of anomalous precipitation increases. The STIO warm SSTA, which is associated with the increase in abnormal precipitation in Jiangnan in May, has been maintained from March to May since 2006, and WNAPAC has played a role as a link. If the trends change are removed, it is difficult for the SSTA in STIO to affect the abnormal precipitation in Jiangnan in May through WNAPAC since 2006.

• A comparative analysis of the characteristics, triggering and maintenance mechanisms of two mesoscale convective systems causing heavy rainfall in eastern Gansu on July 15, 2022

  YANG Lijie, LIU Weicheng, LIU Xinyu, JI Kang, TAN Dan, CAO Yanchao

  Available online:December 25, 2024  DOI: 10.3878/j.issn.1006-9895.2407.24015

  Abstract(132) HTML(0) PDF(12.06 M)( 136)

  Abstract:On July 15, 2022, two Meso-Scale Convective(MCS) systems affected the eastern part of Gansu province, causing regional extremely heavy rainfall which breaking the historical extreme value in the northern region and local heavy rainfall in the southeast region of Qingyang City. In this studying, based on multi-source data and ERA5 reanalysis data, the differences in environmental field characteristics , structural morphology , tigger and maintenance mechanism between the two MCSs were named MCS-A and MCS-B according to their chronological order was analyzed. The results show that: (1)MCS-A occured in a warm-zone precipitation phase (00:00-12:00 on the 15th)that was characterized by high cumulative rainfall, long duration, highly convective and smoothly variable precipitation, and a northerly rain band that is stable and less mobile,while MCS-B occured in the frontal precipitation phase (14:00-20:00 ) when the accumulated rainfall was small, short-lasting, weakly convective but drastically varying, and the center of the rain band is southward and rapidly shifting eastward.(2)The cloud top structure of MCS-A was a quasi-elliptical cloud cluster near MCC developed in isolation,and the cold cloud center of TBB≤-70℃ was biased to the rear of the cloud body, with a long life history and slow movement. The convection structure in the lower layer of it was Back-building type and organizes convection through trains effect.The cloud top structure of MCS-B was a persistent elongated convective system derived from the development of multiple MCSs,the cold center tended to the front of the cloud, with a short life history and rapidly movement.The convection structure in the lower layer of it was Trailing Stratiform type .(3)MCS-A was triggered by the formation of a “eight” convergence line between the ground-based cold pool and the ambient winds , which was maintained quasi-stationary for a long period of time through the mechanisms of organizing convection by balancing the outflow from the cold pool with the low-level vertical wind shear, the supplemental water vapor and dynamical mechanisms of the wind speed pulsation in the low-altitude rapids, and the offsetting of advection and propagation effects in the convective storms.MCS-B, on the other hand, was triggered by multi-scale weather systems such as cold fronts, surface convergence lines, and 700hPa shear lines to trigger convective priming, and then sustained by stronger moisture transport and frontal generation in the lower and middle levels, and by the intrusion of cold air in the middle and upper levels. The life history is short and fast-moving due to factors such as small vertical wind shear in the lower levels and consistent direction of advection and propagation in convective storms.

• The Multiscale Features of Boreal Winter Northeast Cold Vortex and Its Intraseasonal oscillations" Influence on Extreme Low Temperatures in the Northeast-North China Region

  Wang Chen, Gao Qingjiu, Xu Qihui, Fang Zixuan

  Available online:December 24, 2024  DOI: 10.3878/j.issn.1006-9895.2411.24078

  Abstract(29) HTML(0) PDF(9.88 M)( 136)

  Abstract:Utilizing the ERA5 daily reanalysis dataset provided by the European Centre for Medium-Range Weather Forecasts (ECMWF), an objective identification is carried out to obtain the Northeast Cold Vortex (NECV) during the winter season from 1979 to 2020 and the life cycle, intensity, spatial distribution, and number of active days of NECV are explored. Furthermore, an Index of Northeast Cold Vortex (NECVI) is defined to analyze the multiscale features of NECV activity. Based on NECVI, Singular Value Decomposition (SVD) and regression analyses were performed to examine the influence of NECV on winter temperatures in Northeast and North China (NE-N) on intraseasonal scale. Results showed that over the 42 years, there were a total of 266 occurrences of NECV activity during the winter season within the identification area (35°N -60°N, 115°E -145°E), mainly located in the northern part of the identification area (45°N-60°N, 115°E-145°E), with an average life cycle of 4.3 days. The NECV activity does not show a significant linear trend or interdecadal variability, but there is a robust interannual variability with the main period of 2.2-2.5 years, while the intraseasonal oscillation period of the winter NECV is primarily 10-40 days. The SVD and regression analysis indicate that when there is a large-scale low-frequency cold temperature event occurs in the NE-N region, there lies a zonally low-frequency wave train with alternating positive and negative centers from the high-latitude areas of Western Europe to Northeast Asia, meanwhile, the Northeast region is often accompanied by strong cold vortex activity, and the occurrence of low-frequency cold temperatures in the NE-N region lags the low-frequency NECV by about 3-5 days.

• The Influence of Thermal and Momentum Transport at Different Subseasonal Scales on long-duration Ural Blockings in Winter

  Xu Binyu, Yao Suxiang

  Available online:December 11, 2024  DOI: 10.3878/j.issn.1006-9895.2408.23165

  Abstract(20) HTML(0) PDF(4.14 M)( 178)

  Abstract:In winter, the long-duration blocking highs often cause the accumulation of cold air with greater intensity, which lead to the occurrence of widespread severe cold waves, and the study of the establishment and long-term maintenance mechanism of blocking highs has great scientific significance. By used the ERA5 daily reanalysis data provided by the European Centre for Medium Range Weather Forecasts (ECMWF) from 1979/1980 to 2019/2020, 6 long-duration blocking high events (the lifetime is equal or greater than 10 days) were selected from 114 Ural blockings (UB) during the last 41a winter. The similarities and differences between the long-duration blockings and other blockings were compared, focusing on the thermal and momentum transport characteristics at different subseasonal scales during the development and maintenance of long-duration blocking highs. The results show that: (1) The geopotential height in Ural Mountains exhibits significant intra-seasonal oscillations, and the establishment and maintenance of long-duration blockings mainly depends on intra-seasonal scale component (20~80 days) of the geopotential height anomaly, while the establishment and maintenance of other blockings depends on the quasi-biweekly scale component (10~20 days) and intra-seasonal scale component, respectively. (2) During the development stage of long-duration blockings, both the quasi-biweekly and intra-seasonal scale components of stationary thermal flux gradient are beneficial to the increase of geopotential height, and the quasi-biweekly scale heat transport contributes more, while the intra-seasonal heat transport is the largest contributor in the maintenance stage. In comparison, only intra-seasonal heat transport is beneficial to the establishment of other blockings, with decreasing in values that is not favourable for its maintenance. (3) The influence of momentum transport on blocking high events cannot be ignored. The development of blockings is the result of quasi-biweekly and intra-seasonal scale momentum transport. However, the quasi-biweekly scale momentum transport is concentrated in the early part of development stage, while the intra-seasonal scale momentum transport occurs throughout the development stage in the long-duration blockings. In other blockings, the momentum transport is relatively small. During the maintenance stage, the long-duration blockings is dominated by intra-seasonal scale component of stationary momentum flux, and the other blockings is dominated by quasi-biweekly scale component.

• Different characteristics of the interannual variation in summer monthly precipitation over the Indochina Peninsula

  Huo Jianan, Ren Baohua, Li Chaofan, Zhou Xingyan, Song Tianyuan

  Available online:December 11, 2024  DOI: 10.3878/j.issn.1006-9895.2405.24031

  Abstract(29) HTML(0) PDF(3.88 M)( 115)

  Abstract:This study focuses on the interannual variation of monthly precipitation in summer (June to September) over the Indochina Peninsula from 1979 to 2019, and finds that the precipitation in different months is obviously independent of each other. Although the summer monthly precipitation is generally affected by the easterly anomalies from the tropical Pacific Ocean and the westerly anomalies from the Indian Ocean, the regulatory factors causing these circulation anomalies are obviously different. The results show that the tropical west Indian Ocean SST anomalies largely modulate the precipitation in June over the Indochina Peninsula. They regulate the vertical movement near the Indochina Peninsula by influencing the convergence and divergence circulation, and result in precipitation anomalies in the Indochina Peninsula. In July, the precipitation over the Indochina Peninsula is closely related to the SST anomalies in the tropical central and eastern Pacific region in the previous winter, which regulate the precipitation by influencing the northwest Pacific subtropical high activities. In addition, the precipitation in August is mainly affected by the simultaneous east-west dipole SST anomalies around the tropical western Pacific and Maritime Continent. These SST anomalies can regulate the precipitation in the Indochina Peninsula through local Hadley circulation anomalies and Rossby waves. Relatively, there isn’t a notably significant large-scale tropical SST signal related to precipitation in the Indochina Peninsula in September. However, it is significantly affected by typhoon activities, particularly along its eastern coastal areas. This study is helpful to further understand the interannual variation of summer monthly precipitation in the Indochina Peninsula, and provides scientific reference for the summer precipitation climate forecast in the Indochina Peninsula.

• Quantitative Analysis of Parameterized Uncertainty of Physical Processes in Rainstorm Simulation over South China

  ZHOUJinxuan, WANGDonghai, ZHANGChunyan, CHENYihao

  Available online:December 11, 2024  DOI: 10.3878/j.issn.1006-9895.2401.23167

  Abstract(24) HTML(0) PDF(6.03 M)( 133)

  Abstract:More and more attention has been paid to the influence of the uncertainty of the physical processes on the prediction accuracy. In this paper, multivariate analysis of variance and Tukey"s test are used to quantify the model uncertainty related to the parameterization of physical processes and to select the optimal parameterization scheme combination. Taking a rainstorm in South China from May 21 to 22, 2020 as an example, the microphysics scheme, boundary layer scheme and cumulus convective scheme, which are closely related to precipitation, are selected to carry out 80 sets of experiments. The results of multivariate analysis of variance show that the microphysics scheme is the most important for precipitation simulation results and model prediction results, and the interactions between different physical processes cannot be ignored. Tukey"s test is used to compare the discrepancy among different parameterization schemes, and the optimal parameterization scheme combination is selected, which is WSM7 scheme + YSU scheme + GF scheme. In addition, this paper compares the differences of different microphysics schemes, and analyse the influence of the differences of microphysics schemes on the precipitation simulation error from the perspective of hydrometeors and microphysics conversion processes. The results show that hail plays an important role in the simulation of the extreme precipitation. The change of rainwater mixing ratio is mainly due to the melting term of ice particles. The evaporation of rain affects the intensity of cold pool through latent heat absorption, and then affects the subsequent precipitation propagation, finally affects the distribution of heavy precipitation.

• Mesoscale Characteristics and Causes of a Local Warm-sector Rainstorm Process in Southern Sichuan

  LI Yongjun, XU Jinbo, LI Xuan, HE Ke, YAN Jing, ZI Jing, LU Ping

  Available online:December 11, 2024  DOI: 10.3878/j.issn.1006-9895.2404.23096

  Abstract(26) HTML(0) PDF(5.93 M)( 109)

  Abstract:Based on the hourly precipitation data from automatic weather stations, hourly temperature data from multi-source fusion, high-altitude observation data, meteorological satellite data of FY-4A, X-band dual polarization radar data and ERA5 reanalysis data , the mesoscale characteristics and causes of a warm-sector rainstorm process in Panxi area, southern Sichuan from 20:00 on October 4th, 2022 to 12:00 on October 5th, 2022 is analyzed.The results show that:(1)This process manifested as a β-γ mesoscale convective system on satellite imagery, which has gone through three stages of developing, strengthening and weakening in Zemulong Village area. The mesoscale convective system of rainstorm tilts east from bottom to top, allowing the convective system to maintain and develop for a longer period.(2)The radar echo in Zemulong Village area shows a strip-shaped distribution, the back-propagation and echo training effects is significant. The strong echo nuclei is relatively low, mostly below 4.5km and its individual nuclei weakens rapidly, thus it has a high precipitation efficiency.(3)In this process,the atmosphere is in an unstable state of dryness above and wetness below, with a low level of CCL, LCL, LFC, thus the gas mass does not need to be lifted too strongly to move upward vertically and cause water vapor condensation, then the thunderstorm system can develop rapidly. The weak vertical wind shear also reduces the involvement of unsaturated dry cold air, weakens the entrainment rate and improves the precipitation efficiency. (4)The convergence and cyclonic flow field formed by the blocking effect of the terrain on the northwest edge of Panzhihua are the main factors generating the continuous convection and forming the training effects, thus extreme precipitation occurs in Zemulong Village area. In Guanyintang Village, the southwest low-level jet stream is nearly orthogonal to the northeast mountains, which force the airflow to rise and forming strong precipitation in the low-lying areas in front of the mountain. Due to the southwest low-level jet, convergence of wind speeds caused by terrain, the terrain circulation caused by terrain temperature gradient also promotes the formation of heavy precipitation.

• Vertical Structures and Temporal Variations of Clouds over the Mountainous Area of Fujian, China

  ZHENG Jiafeng, PENG Tingwei, LIU Yihua, ZHANG Haoran, ZENG Zhengmao

  Available online:December 09, 2024  DOI: 10.3878/j.issn.1006-9895.2410.24052

  Abstract(30) HTML(0) PDF(2.94 M)( 105)

  Abstract:The observation and study of clouds are of great importance for the development of numerical models, climate change estimation, weather modification, etc. To advance the understanding of structural characteristics and temporal variations of clouds in the mountainous areas along the southeast coast of China, observations from a ground-based Ka-band millimeter-wave cloud radar deployed in Jian"ou of northern Fujian, China, between 2019 and 2022, were utilized to study the characteristics, seasonal patterns, and diurnal variations of cloud occurrences, vertical structures, and parameters in this area. Additionally, the causes underlying these observed characteristics and variations are also discussed from atmospheric water vapor and thermodynamic conditions. The findings indicate that: (1) Cloud occurrence exhibits seasonal variations, with the highest occurrence observed during spring, followed by summer and winter, and the lowest during autumn. Low and high clouds dominate during spring and summer, whereas low and mid-level clouds are predominant during autumn and winter. (2) Radar reflectivity factors of high clouds are generally larger than those of low clouds during spring and summer. In summer, both ice-phase and liquid-phase cloud layers exhibit the largest radar reflectivity factors, followed by spring and autumn, and the smallest reflectivity factors are observed during winter. Cloud base height and top height are highest during summer, followed by spring and autumn, respectively, while they are lowest during winter. The thickest cloud layer and largest cloud gap distance also occur during summer, followed by spring and autumn, respectively, whereas the thinnest cloud layer and smallest cloud gap distance are observed during winter. (3) Diurnal variations in cloud vertical structures and parameters are significant in different seasons, and their differences are also apparent. Compared to spring, summer exhibits earlier and stronger convection activities and a longer lifespan, resulting in larger and longer-lasting variations in cloud parameters during the afternoon. Diurnal variations in cloud occurrence, intensity, and other cloud parameters are less pronounced during autumn and winter compared to spring and summer. However, the diurnal variation trend of clouds in autumn is similar to that in summer, while the diurnal variation trend of clouds in winter is similar to that in spring. (4) Average specific humidity, horizontal wind field, and convective available potential energy show significant positive correlations with the seasonal and diurnal variations in cloud radar-observed cloud-related changes in the local area.

• The nonstationary relationship between NAO and summer precipitation in the eastern Tibetan Plateau

  CHEN Tao, ZHI Hai, CHEN Lin, ZHUO Ga, DEKEY Yangzom

  Available online:November 21, 2024  DOI: 10.3878/j.issn.1006-9895.2404.23115

  Abstract(27) HTML(0) PDF(1.74 M)( 129)

  Abstract:Precipitation on the Tibetan Plateau (TP) have received attention because of its importance for regional water cycle. Based on data of 96 meteorological stations from 1961 to 2017 on the eastern TP, the relationship between the lead mode of summer (JJA) precipitation variability and the North Atlantic Oscillation (NAO) is analyzed, and the possible mechanisms for the unstable relationship are explained. The results show that the NAO dominates the leading mode of summer precipitation on the eastern TP, but there are interdecadal variations in their relationship, with NAO leading to a north-south dipole pattern in the early period (1961-1993), and a monopole pattern in the later period (2002-2017). The NAO is able to stimulate potential height anomalies with a quasi-barotropic structure in the upper layers over the TP, and form corresponding circulation anomalies in the lower layers, which in turn affect the water vapor anomalies in the region. During the early (later) period, the west edge of the NAO-related circulation anomalies is located in the northeastern (northwest) TP, which is conducive to the formation of precipitation anomalies of north-south dipole pattern (monopole pattern) in the eastern TP. The shift in the leading modes of summer precipitation on the eastern TP resulted in an abrupt change in the NAO-precipitation relationship in 1998 for the entire study period. Given the nonstationary relationship between NAO and summer precipitation on the eastern TP, the interdecadal background signal needs to be considered in the study of NAO’s impact on regional climate in order to improve the prediction level and model simulation capability.

• Impacts of high temperature and drought on extreme vegetation productivity losses in China from 1982 to 2016

  ZHAO Dongyuan, ZHANG Lixia, SUN Yankun, YU Xiaojing

  Available online:November 21, 2024  DOI: 10.3878/j.issn.1006-9895.2406.23169

  Abstract(19) HTML(0) PDF(4.26 M)( 113)

  Abstract:Investigating the impact of high temperature and drought on extreme vegetation productivity losses is crucial for a better understanding ecosystem extremes, facilitating better adaptation to climate change and mitigating their impacts on agricultural production and socio-economic systems. Based on five sets of Gross Primary Productivity (GPP) datasets, we study the contribution of high temperature and drought to extreme GPP losses in China from 1982 to 2016, from the perspective of climatology and long-term trends. In terms of climatology, the extreme GPP losses area-averaged in China is -15.7 gC m-2 yr-1. The frequency and contributions of high temperature and drought are comparable, with drought, high temperature, and combined high-temperature and drought events contributing 45%, 41%, and 23%, respectively, to the total GPP losses. As for the long-term trends from 1982 to 2016, more than 55% of areas in China has experienced an increase in extreme GPP losses, with a regional mean of -2.46 gC m-2 35 yr-1. The increasing frequency of high-temperature, drought, and combined high-temperature and drought events all contribute to this trend significantly, with drought frequency making the largest contribution (-2.47 gC m-2 35yr-1), leading to an increasing trend in over half (61%) of the regions in China. From the perspective of regional distribution, the northern and central China experienced the most significant and pronounced increases in extreme GPP loss from 1982 to 2016. These areas are the hotspots affected by high-temperature and drought. This study quantifies the contribution of the variation in the frequency of high-temperature and drought events in China over the past few decades to extreme GPP loss. It identified the hotspots of terrestrial ecosystems in China where are greatly affected by increasing frequency of high-temperature and drought, thus providing scientific support for a better adaptation and migration to climate change, and sustainable socioeconomic development.

• Analysis of Meteorological Conditions and Microphysical Characteristics of an Aircraft Icing Event

  Zuo Dongfei, Zhao Shuwen, Li Junxia, Gao Yang, Xia Zhaojun, Du Yuanmou‘, 王黎俊

  Available online:November 21, 2024  DOI: 10.3878/j.issn.1006-9895.2403.23155

  Abstract(34) HTML(0) PDF(7.93 M)( 117)

  Abstract:Aircraft icing poses a serious threat to flight safety. To better understand the meteorological conditions and cloud microphysical characteristics of aircraft icing, and to find the relationship between icing and the threshold of macro meteorological conditions, this study used aircraft observation data, combined with radar and ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts, to analyze the weather conditions and cloud microphysical processes of a severe aircraft icing event in central and eastern Henan Province on December 10, 2018. The intensity of the icing event was also assessed. This icing event was caused by the combined effects of an upper-level trough, low-level shear, and surface cold high pressure. Warm and moist air at low levels flowing towards Henan ascended along the cold high pressure, forming an inversion layer with warm air above and cold air below, which facilitated the accumulation of liquid water in the region. The icing area was rich in liquid water content but had low ice water content, liquid water content is significantly higher between the altitudes of 550 to 750hPa compared to other altitudes. The aircraft observation data is relatively consistent with the results of ERA5 reanalysis data, the severe icing area was at an altitude of 3630m, with cloud temperatures between -8.2 and -6.8°C, relative humidity between 87% and 92%, an average cloud droplet concentration of 499.9cm-3, and a maximum liquid water content of up to 0.87g/m3. In this area, large and small supercooled liquid droplets coexisted, with virtually no ice crystal particles. Calculations showed that the thresholds for light, moderate, and severe aircraft icing in areas rich in liquid water content were 0.05g/m3, 0.20g/m3, and 0.58g/m3, respectively. Under conditions where the inversion layer strength was 1.93°C/100hPa, vertical motion speed ranged from -0.25 to 0.2Pa/s, and horizontal convergence intensity was -3.73kg/(m2s), the probability of icing intensity reaching moderate or above was 77%.

• Development of Rapid-refresh Integrated Seamless Ensemble system at hundred-meter resolution scale and its application evaluation in Beijing Winter Olympics

  SongLinye, ChenMingxuan

  Available online:November 21, 2024  DOI: 10.3878/j.issn.1006-9895.2409.23139

  Abstract(25) HTML(0) PDF(3.35 M)( 110)

  Abstract:The 24th Winter Olympic Games in 2022 (referred to as the Beijing Winter Olympic Games) has put forward the rigid demand of "100-meter and minute-updated" meteorological support services, especially for the forecast demand of refined and accurate wind, gust, temperature, rain and snow, etc. In order to achieve this goal, the Institute of Urban Meteorology has developed a high spatio-temporal resolution Rapid-refresh Integrated Seamless Ensemble (RISE) system, which provided fast fusion forecasts based on multi-source data with hundred-meter resolution scale and minute-level update frequency, and was applied during the Beijing Winter Olympic meteorological support service. This paper firstly summarizes the basic framework, core algorithms and technical progress of RISE system. It integrates multi-source observation data and model forecast products including the 5-min updated surface automatic weather stations, 6-min updated weather radars, nowcasting products, meso-scale numerical forecast products and high-resolution real-time large eddy simulation data, and further introduces complex terrain downscaling technology, seamless fusion technology, high-resolution deviation correction technology, etc. It can generate 10-min updated fine grid analysis and future 0-24h forecast products including surface temperature, humidity, wind, gust, precipitation and precipitation types with a horizontal resolution of 500-meter in Beijing-Tianjin-Hebei region and 100-meter resolution in Winter Olympics mountainous region, and also provide 12-hour updated future 0-10d forecasts of conventional meteorological elements with 67-meter resolution in six outdoor Winter Olympic venues. Then, based on the long-term verification and several typical cases, this paper also evaluates the real-time application performance of RISE products during the Beijing Olympic test and race periods, and gives the current level of winter weather prediction over complex mountainous area in Beijing and its surroundings. Finally, the future development and key technical difficulties of "100-meter and minute-updated" weather forecasting technology are discussed. Results of this study can provide precise and accurate objective meteorological forecast support for major events such as the Winter Olympics, and can also be used in daily weather forecast and early warning services, as well as other interdisciplinary fields such as energy and hydrology, which has important scientific significance and application value.

• Comparative analysis of two extreme rainfall triggered by surface convergence lines in Northern Zhejiang

  Shen Xiaoling, Zhou Hongyuan, Wu Zhuoheng

  Available online:November 21, 2024  DOI: 10.3878/j.issn.1006-9895.2407.23158

  Abstract(34) HTML(0) PDF(1.79 M)( 119)

  Abstract:By using conventional observation data、dual polarization radar data、 ERA5(0.25o^×0.25o) reanalysis data,the weather background、environmental conditions、triggering mechanism of mesoscale convective system、radar parameter characteristics of the two extreme rainfall processes in Zhejiang on July 16 and 22, 2023 are compared and analyzed,the result show that：(1)The two processes occurrs in a similar circulation background of 500hPa with westerly trough moving eastward around the Subtropical High, and the typhoon or tropical depression in the South China Sea. Both processes are triggered by the surface mesoscale convergence line.(2)The background of middle-low and precipition area are different,process 1 occurs in cold shear at 850hPa and the rainfall center is located at the edge of the Subtropical High,while process 2 occurs in consistent southwest airflow at 850hPa and the rainsfall center is located in Subtropical High circulation.(3)The thermal and dynamic conditions are different,the extreme rainfall of process 1 occurs in the process of 850 and 925hPa southeast airflow enhancement, the boundary layer airflow is more significant, the atmospheric stratification is unstable,

• A study on the characteristics and driving mechanism of carbon exchange between the Zoige alpine wetland and atmosphere

  CHEN Yixuan, WEN Jun, TU Zhenwu, YAN Jin

  Available online:November 20, 2024  DOI: 10.3878/j.issn.1006-9895.2408.24025

  Abstract(42) HTML(0) PDF(2.26 M)( 79)

  Abstract:In the context of global warming, the carbon process of alpine wetland ecosystems is complex and sensitive. However, the long-term dynamics and driving mechanisms of carbon balance in alpine wetland ecosystems are still unclear. In this study, the carbon dioxide (CO2) flux measured by eddy covariance technique is used to analyze the CO2 exchange flux of the Zoige alpine wetland from 2017 to 2021, as well as the dynamics and driving mechanisms of CO2 exchange flux. The results showed that during the vegetation growing season (June - October), the annual gross primary productivity (Gross Primary Productivity, GPP) and ecosystem respiration (Ecosystem espiration, Re) of the ecosystem showed an unimodal pattern, while the annual net ecosystem CO2 exchange (Net Ecosystem Exchange, NEE) of the ecosystem showed a V-shaped trend. The Zoige alpine wetland ecosystem is a carbon sink during the growing season, which is a carbon exchange process between land and air that absorbs more than releases. The daily average NEE, GPP, and Re over the years reached -3.10±4.61, 4.78±5.61, and 1.65±1.56 umol(m2·s), respectively. On the monthly scale, the effects of air temperature (Air Temperature, Ta), soil temperature (Soil Temperature, Ts), photosynthetic photon flux density (Photosynthetic Photon Flux Density, PPFD), precipitation (Precipitation, PPT), air relative humidity (Air Relative Humidity, RH) and vapor pressure deficit (Vapor Pressure Deficit, VPD) on NEE, GPP and Re were analyzed by the regression analysis. The results showed that Ta, Ts and PPT were the main determinants of monthly NEE changes, and NEE was negatively correlated with them. Ts and Ta largely determined the monthly variation of GPP, which is positively correlated with it. Ts ,Ta and PPT are the main determinants of monthly Re variation, and Re is positively correlated with them. The Classification and Regression Tree (Classification and Regression Tree, CART) algorithm was used to analyze the effects of various factors on carbon exchange flux in the daily scale. The results showed that soil temperature had a great influence on daily GPP and Re, and temperature is the main controlling factor for daily NEE. The results of this study provide important data and reference for understanding the carbon budget of alpine wetland ecosystems.

• Multi-scale characteristics of an extreme rainstorm in North China on July 2023

  LIU Longsheng, LIU Lu, LI Ying

  Available online:November 07, 2024  DOI: 10.3878/j.issn.1006-9895.2405.23135

  Abstract(32) HTML(0) PDF(126.36 M)( 146)

  Abstract:The multi-scale characteristics of an extreme rainstorm in North China on July 2023 were studied using ERA5 reanalysis data with the spatial resolution of 0.25° × 0.25° and JMA GSMaP precipitation data with the spatial resolution of 0.1° × 0.1°. Results showed that the extreme rainfall episode in North China was formed under the combined effect of monsoon vortex in the Bay of Bengal, remnant of Typhoon Doksuri, Typhoon Khanun, upper- and low-level jet, high blocking and terrain elevations. The configuration of multi-scale weather systems was unlike any previous extreme rainstorm process. The Bay of Bengal monsoon and Typhoon Khanun provided favorable conditions for transportation of water vapor during the continuation of precipitation. A high blocking to the north of North China caused the accumulation of water vapor from low latitudes to gather at east of the Taihang Mountains. The remnant vortex of Doksuri obtained water vapor and was situated at the southern foothills of the Taihang Mountains. The horizontal potential gradient formed by this remnant vortex, along with the blocking high pressure to its north and the western North Pacific subtropical high to its east, promoted the development and intensification of a low-level jet. The coupling of 850 hPa low-level jet and 200 hPa high-level jet continuously generated mesoscale convective clouds on the windward slopes of the Taihang Mountains. When ground winds in North China were nearly perpendicular to topography, pronounced forced lifting motion due to topography further organized and developed mesoscale convective clouds, resulting in short-term heavy precipitation. The first stage of intense precipitation occurred when atmospheric stratification was vertically convectively stable. However, intensified boundary layer low-level jet promoted inclined upward flow over windward slopes, triggering release of conditionally symmetric instability energy and leading to heavy precipitation. The second stage mainly occurred in warm sectors with atmospheric stratification showing vertical convective instability triggered by terrain-induced dynamical forcing.

• Properties of Hail Events and Spectrum Distribution during 2018–2023 in Honghe, Yunnan

  Zheng Jiao, 郭欣, Guo Xueliang

  Available online:November 04, 2024  DOI: 10.3878/j.issn.1006-9895.2407.24007

  Abstract(131) HTML(0) PDF(2.75 M)( 121)

  Abstract:The Yunnan-Kweichow Plateau is one of regions with high frequent hail events in China, however, the relevant studies on hail properties are few. On basis of 93 minus-level spectrum data collected from 60 hail events by 13 national meteorological stations in Honghe, southern Yunnan during 2018–2023, the annual, seasonal, daily and geographic distributions of the number of hail days, hail size and hailfall duration, as well as hail type and spectrum distribution are investigated in this study. Results show that the annual mean number of hail days was 10 d, with a maximum number of 24 d and minimum number of 3 d. The annual mean maximum hail size was 9–16 mm, and hailfall duration was 2–5 min. The number of hail days had apparent seasonal and diurnal variations. The number of hail days was 33 d in spring for six years, which accounted for more than 50 % in 60 d in total during this period, and least in autumn. The number of hail days mainly occurred in the afternoon and evening. The overall hail spectrum distribution was unimodal. There were higher hail number concentrations in spring and summer seasons with the maximum hail size of 19 mm in diameter, and was dominated by high-density hail. There was very low amount of low-density hail and graupel. Hail events had apparent geographic distribution properties. The western and southern subregions had the highest number of hail days, which was dominated by high-density hail and graupel and low-density hail were few. Therefore, hail events in the honghe region, Yunnan primarily occurred in spring and in the afternoon and evening. Hail events had short duration and were dominated by high-density small-sized hail. There was very low concentration in low-density hail and graupel.

• Comparative Analysis of the Effects of High-frequency and Low-frequency ISO in Mid-High Latitude Eurasia on Surface Ozone Concentration over North China during boreal summer

  Fan Yanbin, Yang Shuangyan

  Available online:October 21, 2024  DOI: 10.3878/j.issn.1006-9895.2304.23146

  Abstract(41) HTML(0) PDF(8.02 M)( 226)

  Abstract:This study, based on ERA-5 reanalysis data, contrasts the spatiotemporal evolution characteristics of two types (10-30 days and 30-60 days) of intra-seasonal oscillations (ISO) in mid-high latitude Eurasia during boreal summer. Meanwhile, using the daily maximum 8-hour average ozone concentration published by the China National Environmental Monitoring Center to analyse the influence of HF-ISO and LF-ISO on surface ozone pollution in North China. The results indicate that the occurrence frequency of HF-ISO is higher than LF-ISO, and the intensity of HF-ISO is also stronger than LF-ISO. HF-ISO will propagate southeast from the mid-high latitude Eurasia by phase in a constant speed. While the LF-ISO tends to intensify and linger in the Siberian region for an extended period before propagating southward. Both ISOs exhibit a quasi-barotropic structure. The results of wave flux show that the southeast propagation of Rossby wave energy is conducive to the southeast propagation of temperature anomalies. As SAT anomalies spread southward to North China, they affect local weather conditions. The distribution of ozone concentration anomalies suggest that two types of ISOs can modulate precipitation, relative humidity, and total cloud cover, consequently affecting temperature anomalies to influence surface ozone concentration. Because of the slightly different geographical influences for two types of ISOs, the corresponding surface ozone pollution anomalies are different. These results indicate both ISOs can influence surface ozone concentration, which provide valuable insights for pollution control efforts for North China.

• Comparison of the performance of multiple operational models on prediction of heavy rain caused by residual vortex of Typhoon Doksuri (2305)

  Liu Yanjie, Wang Xiaocong, Liu Yimin, Wang Jincheng, Yin Qing, Miao Hao, Wang Kai

  Available online:October 14, 2024  DOI: 10.3878/j.issn.1006-9895.2405.24037

  Abstract(22) HTML(0) PDF(40.53 M)( 337)

  Abstract:Due to the residual circulation of Typhoon Doksuri (2305), heavy rainstorm events occurred in North China during July 29 to August 1, 2023. This study evaluated the performance of three operational models at varying forecast lead time, including the Integrated Forecast System of European Centre for Medium-Range Weather Forecasts (EC-IFS), the Global Forecast System of National Centers for Environmental Prediction (NCEP-GFS) and the China Meteorological Administration Global Forecast System (CMA-GFS). The possible causes of the forecast biases are also analyzed. Results show that: (1) The forecast capability of the three models decreases with the increasing forecast lead time. Among all, EC-IFS outperforms the other two models with averaged spatial correlation coefficient (SCC) over 0.5 at lead time 24-120 h, SCC of NCEP-GFS approximates EC-IFS when leads 24-48 h but significantly decreases and fluctuates after 72 h, whereas that decreases to negative values in CMA-GFS. (2) In terms of rainfall location, EC-IFS well reproduced the distribution pattern of the heavy rain, while the forecasted rainfall in NCEP-GFS locates to the south of the heavy rain due to the eastward location of the forecasted subtropical high and weakened south flow; CMA-GFS predicts rainfall noticeably eastward, which is mainly caused by shifted subtropical high and continental high, allowing the residual vortex to move northward. As for intensity, all three models commonly underestimated the extreme value of heavy precipitation. (3) Vertical structures of diabatic heating indicate that the difference of model performance is mainly due to the uncertainties of parameterization for model physical process. Almost all models are unable to accurately simulate the precipitation-relative humidity tilting structure as in observation, implying that models still have deficiencies in parameterizing sub-grid physical processes such as convection and clouds, which are the main causes of model forecast bias.

• Analysis of Microphysical Characteristics and SLR of Two Rain and Snow Weather Processes in the Same Period of Winter Olympics

  Du Jia, Yu Bo, Fu Jiaolan

  Available online:September 04, 2024  DOI: 10.3878/j.issn.1006-9895.2407.23157

  Abstract(43) HTML(0) PDF(4.53 M)( 907)

  Abstract:The microphysical characteristics and different snow liquid ratios (SLR) of rain to snow and snowfall processes during the same period of Beijing Winter Olympics were analyzed based on Parsivel data, densely artificial snow-depth measurement and microscopic snowflake shape observation. The average particle spectrum showed a unimodal pattern, with snowflake spectrum having the highest peak number concentration and raindrop spectrum having the lowest. During the same snowfall process, the peak number concentration of plate or column ice crystals was higher than that of dendritic snowflakes. The average falling speed of particles falling below 2 m/s can be used as an indicator of phase transfer. The average falling speed of dry snow particles was less than 1 m/s. The ambient air temperature during the rain to snow process on February 13-14, 2020 was relatively high. The growth of snowflakes in the sleet stage mainly came from the riming process. With the decrease in temperature at lower levels and the significant increase in humidity at -18~-12℃ layer, precipitation phase turned to snow and the riming process still existed. Under the joint action of riming and adhesive aggregation processes, the maximum crystal diameter reached 19mm, but the snow liquid ratio was low to 0.6cm/mm. In the snow process during the Winter Olympics, the temperature was lower with low level cloud region between -18 and -12℃, and the falling velocity was close to the classical curve of the unrimed ice crystals, so the snowflakes were all unrimed. The combined action of sublimation, Bergeron process, and hook aggregation made the particle diameter grow to 11mm. But the snowflakes’ shape changing to plate or column was observed at Shougang Venue, resulting in the increase of the number concentration and reduction of particle spectrum width, while the corresponding SLR sharply reduced.

• Classification of the subseasonal meridional march of summer precipitation anomalies over eastern China and possible mechanism

  Li Juan, Wang Cheng, Hsu Pangchi, Zhu Zhiwei

  Available online:September 04, 2024  DOI: 10.3878/j.issn.1006-9895.2402.23144

  Abstract(46) HTML(0) PDF(12.46 M)( 626)

  Abstract:Understanding the classification of the subseasonal meridional march of summer precipitation anomalies in eastern China has important influence on understanding dynamic process of East Asian summer monsoon and prediction of rainband. However, previous studies for classification of precipitation focus on subseasonal propagation for local precipitation, while the regularity and classification of subseasonal march of summer precipitation anomalies over eastern China is still unclear. Therefore, in this study the subseasonal meridional movement of summer (24-50 pentad) precipitation anomalies over eastern China has been classified into three categories by using K-means clustering method: 1) the northward propagating type in which the precipitation anomalies move northward from South China; 2) the oscillating type in which the precipitation anomalies are stable and the phase is reverse in the north and south of 30oN; 3) the southward retreating type in which the precipitation anomalies move southward from the Huang-Huai River Basin. Furthermore, it can be observed that the anomalous convection over tropical Indian Ocean propagates northeastward in all three types. However, whether the precipitation anomalies can propagate to eastern China largely depends on the movement speed and intensity of the mid-latitude disturbance over East Asia. When the westerly jet over eastern China is strong and wide, the mid-latitude disturbance moves eastward quickly. While the wave activity flux propagated to East Asia is inactive, the mid-latitude disturbance is hard to develop. In this case, tropical anomalous convection is prone to propagate northward and form the northward propagating type. If the westerly jet over eastern China is weak but the wave activity flux propagated to East Asia is active, the mid-latitude disturbance moves slowly and is stable. It can develop and enhance due to active upstream wave energy transport, thus blocking the northward propagating of the tropical anomalous convection and forming the oscillating type. When the westerly jet over eastern China is strong and wide, and the wave activity flux transported to East Asia is active, the mid-latitude disturbance can be strengthened and propagate southward, formulating southward retreating type.

• Optimization of Localized Land Use Structure for Low-Carbon and Its Wind-Thermal Environment Change Experiment

  Yang Bao Gang, Zhu Hao Nan

  Available online:September 02, 2024  DOI: 10.3878/j.issn.1006-9895.2406.23160

  Abstract(50) HTML(0) PDF(1.61 M)( 727)

  Abstract:Constructing low-carbon and livable new cities is a new concept and trend in urban development. Considering simultaneously low-carbon emissions and climate adaptability improvements in urban planning and construction holds paramount significance. This approach plays a critical role in mitigating the effects of climate change throughout the urbanization process and enhancing the overall quality of urban life. This study selected the Chongqing Economic and Technological Development Zone as the experimental area, employing linear programming to conduct low-carbon optimization on the planned land use structure for the year 2025. Utilizing a micro-scale numerical model, the changes in wind-thermal environment were simulated within the experimental area for both January and July following the optimization of land use for low-carbon and spatial efficiency. The results indicate that the following: (1) After optimizing the land use structure for low-carbon, the experimental area reduced carbon sources such as construction land while increasing carbon sinks like forests and grasslands. The total annual land carbon emissions decreased by 19.0×104 tons, a reduction of 12.1%. (2) The combination of low-carbon optimization and spatial optimization improved the ventilation environment in the experimental area. In January and July, the average wind speeds increased by 0.8% and 1.7%, respectively, with local maximum increases of 8.0% and 11.0%. Average wind speeds increased at 61.1% and 74.4% of the locations, and an observed increase in average wind speed occurred at 12 time points and 18 time points in the daily hourly sequence, respectively. (3) After optimization, the urban heat island effect in the experimental area tended to alleviate. The average temperatures in January and July showed reductions of 1.3% and 0.7%, respectively, with maximum localized decreases of 12.9% and 5.0%. Average temperatures decreased at 61.2% and 57.7% of the locations, and all time points in the daily hourly sequence showed a decrease in average temperature. Optimizing urban land use structure for both low-carbon and spatial efficiency holds the potential to concurrently reduce carbon emissions, improve wind-thermal environment, and enhance urban climate adaptability. The results of simulation evaluations can serve as valuable references for establishing quantitative objectives in economic and social development planning, and informing key indicators for comprehensive urban planning.

• The Improvement of China Annual Precipitation status index and Its Predictive Factors

  MA Kangjie, GONG Hainan, WANG Lin, LI Yulan

  Available online:August 28, 2024  DOI: 10.3878/j.issn.1006-9895.2405.24013

  Abstract(65) HTML(0) PDF(5.71 M)( 720)

  Abstract:The annual climatic status is the comprehensive representation of the climate of a year, which can indicate the degree of deviation of the main climatic elements from the climatic normal. As an important part of the annual climatic status, the annual precipitation status comprehensively reflects the deviation of the precipitation from the climatic normal. Based on the observational data and reanalysis data, this study evaluates the index of annual precipitation status of predecessors. It is found that due to the regional average of all grid points with equal weights, the reason for some bad status years is that the contribution of the western region is relatively large, so the total effect is not satisfactory. Therefore, the climatology of precipitation and population density are considered as weights to improve the index of annual precipitation status, and we called this “improved index”. The historical climate data are used to verify the improved index, and the results show that the good and bad status years are well selected by the improved index. In addition, the characteristics and precursor signals of good and bad status years are analyzed. The results show that the sea surface temperature (SST) and 850 hPa wind field in good status years are very close to the climatology, but the bad status years are quite different from the climatology. According to the percentage of precipitation anomalies, we divide the bad status years into drought years and flood years. It is found that the SST in the Northwest Pacific is significantly colder in the drought years, and there is a significant northerly wind anomaly in the central and eastern China. However, in the flood years, the SST in the northwestern Pacific Ocean and the tropical Indian Ocean is significantly warmer, and there is a significant southwesterly wind anomaly in southern China. The results of the precursor signals show that the precipitation in the second year can be predicted based on the absolute value of the SST anomalies in the western Indian Ocean in the previous autumn. The mechanism may be the effect from the El Ni?o in the previous autumn to the IOBW in spring and summer, which is beneficial to the maintenance of anomalous anticyclones over the Philippines and the South China Sea, resulting in a significant southwesterly wind anomaly at 850 hPa, transporting water vapor, and leading to increased precipitation in China. In addition, the asymmetric effects of El Ni?o and La Ni?a on China are verified by the SST in the previous autumn, which is reflected in the asymmetry of drought and flood years. The results in this paper have certain reference significance for understanding and predicting the precipitation in China.

• Ocean surface wind field retrieval and validation from FY-3E/WindRAD dual-frequency scatterometer

  fanghe, Li Zhengquan

  Available online:August 27, 2024  DOI: 10.3878/j.issn.1006-9895.2407.23170

  Abstract(52) HTML(0) PDF(1.58 M)( 725)

  Abstract:The FY-3E satellite launched in July 2021, which is the world"s first civilian twilight orbit meteorological satellite. The WindRAD dual-frequency scatterometer it carries has the ability to detect global ocean surface wind fields. This paper first studies the nonlinear relationship between sea surface backscatter and wind field based on FY-3E/WindRAD L1 level observation data, and then establishes geophysical model functions (GMFs) for C- and Ku-band VV/HH polarization wind field retrieval respectively. Based on the maximum likelihood estimation (MLE) method, ocean surface wind field were retrieve from WindRAD scatterometer data. The wind field is validated using ocean buoy, CSCAT and NCEP wind field data. The results show that the wind speed bias between the WindRAD and buoy is about 0.2m/s, and the root-mean-square error (RMSE) is range from 1.20 to 1.44 m/s, which better than 2m/s for operational applications. The wind direction bias and RMSE are range from 1.4 ~ 3.0° and 25.3 ~ 30.0°, respectively. WindRAD and HSCAT wind fields have good consistency, with the RMSE of wind speed between 1.37~1.6m/s and the RMSE of wind direction between 22.9°~25.9°. The RMSE between WindRAD and NCEP wind speed is 1.87~2.12m/s, and the RMSE of wind direction is between 22.3°~27.1°. These results indicate that sea surface wind fields retrieved from WindRAD dual-frequency scatterometer have high accuracy, fully demonstrating the application potential and value of WindRAD payload in global sea surface wind field detection.

• Observational analysis of Mount Taihang’s Orographic Effects on the “23.7” Extreme Precipitation Event in North China

  LI XIAOLAN, CHEN TAO

  Available online:August 23, 2024  DOI: 10.3878/j.issn.1006-9895.2403.23161

  Abstract(43) HTML(0) PDF(11.49 M)( 682)

  Abstract:Based on high-resolution multi-source observational data, the topographic effects of the Taihang Mountains on intensity, centers and convective development characteristics of the extreme precipitation struck North China was analyzed. This long-lasting, widely impacting extreme precipitation event with high-intensity was primarily caused by the northward movement of the remnant circulation of Super Typhoon Doksuri, with the maximum cumulative precipitation up to 1003.4 mm. And the extreme rainfall area and the recording-broken daily precipitation were distributed on the upwind slope on the eastern side of Taihang Mountain. The peak of the cumulative precipitation occurred at the altitude of about 400 m on the upwind slope, and centers of accumulated precipitation above 600 mm were located on the inner corner of open-valley terrain composed of mesoscale mountains on the eastern side of Taihang Mountain. Due to the blocking effect of the northern continental high, the Western Pacific Subtropical High and the topography of the Taihang Mountains and Shanxi Plateau, the residual vortex of Doksuri moved slowly since July 29. The Beijing-Tianjin-Hebei region has been dominated by convergence induced by the inverted-trough on the north side of the vortex and the topographical blocking, forming synoptic uplifting. Low-level easterly jet formed between the typhoon residual vortex and the high pressure barrier. As a result, water vapor flux climbed from the boundary layer over the plain to the upslope of the Taihang Mountains. The convergence center of water vapor flux and the upward movement occurred near 950-925hPa on the mid-slope, which was conducive to the formation of precipitation peak on the mid-slope. The fine terrain of the Taihang Mountains took significant impact on the occurrence and development of the Mesoscale Convective System (MCS). On the night of July 29, the MCS approaching to the upwind slope was significantly enhanced, and under the northeast wind background in front of the mountain, a convergence center was formed on the inner side of the mesoscale trumpet shaped terrain, leading to sustained heavy precipitation. Because of the boundary organization of the cold pool on the east boundary of MCS, the initiation and development of the new convection led to short-term rainstorm in the piedmont plain. On the night of July 30, under the organization of the southerly boundary jet and the topographic vortex circulation, the locally developed meso-β scale linear MCS caused an extreme rainfall intensity exceeding 100 . This study deepens the scientific understanding of the mechanism of extreme precipitation in North China and helps to provide a reference for future forecasting decisions.

• Characteristics of Low-Level jets over the West Coast of Guangdong Province during the first rainy season in South China and its influence on Orographic Precipitation

  Chen Xiaoqing, Cai Jingjiu

  Available online:July 25, 2024  DOI: 10.3878/j.issn.1006-9895.2406.23082

  Abstract(52) HTML(0) PDF(2.58 M)( 718)

  Abstract:In this study, based on the Hailing Island wind profile radar observation data, precipitation data of Automatic Weather Station and ERA5 reanalysis data during the first rainy season of 2014-2016 in South China, we investigate the structural characteristics, diurnal variation characteristics and formation mechanism of low-level jets (LLJs) over the west coast of Guangdong Province. The effects of low-level boundary layer jets with different intensities on the temporal and spatial distribution of orographic precipitation in three key regions of Guangdong are also discussed. Results show that: (1) Based on the classification criteria of LLJs proposed in this study, the cumulative occurrence probability of LLJs is 21.2%. Most LLJs fall into the class 1-3 category, and class 4 is less common. 77.1% of the speed of LLJs are less than 14 m?s-1, 84.7% of the direction of LLJs are southwest. Most of the vertical shear of wind speed below the maximum wind speed of LLJs are between (5～25) ×10-3s-1. The height of the maximum wind speed of LLJs show a bimodal structure, and most of LLJs appear in the boundary layer within 1 km. (2) The synoptic-system-related LLJs (SLLJ) show a nocturnal peak, while the boundary layer jets (BLJ) show a double peak at midnight to the early morning and afternoon. The inertial oscillations triggered by the local-scale land-sea breeze circulation is responsible for nocturnal peak of BLJ. The pressure difference between the low latitude Asian continental low pressure and the Northwest Pacific Ocean high pressure near the surface, plays a key role in the formation of BLJs with different intensities. The development of continental low pressure during daytime is the main reason for the formation of afternoon peak of strong BLJ. (3) The influencing mechanism of BLJs on the distribution and intensity of orographic precipitation in Guangdong Province is complex. The orographic precipitation on the windward slope of large scale mountains dominates the inland of northern central Guangdong and coastal areas of eastern Guangdong. The stronger the BLJs, the stronger the orographic precipitation. The locations of the heavy orographic precipitation along the east coast of Guangdong are stable, while the inland orographic precipitation center in northern central Guangdong moves northwest with the intensification of BLJ. In the coastal area of west Guangdong, the windward slopes and the downwind slopes of the the medium and small-scale mountains, the lee-side wake convergence area of the terrain can produce obvious orographic precipitation. The heavy orographic precipitation must occurs under the background of suitable low-level inflow wind speed. (4) Under the influence of different intensity BLJ, the orographic precipitation in the inland regions of central and northern Guangdong shows a bimodal structure in the afternoon and in the morning. While the precipitation intensity of the afternoon peak is about twice that of the morning peak, the precipitation intensity of the bimodal peak increased with the strengthening of BLJ. As the intensity of BLJ increases, the diurnal bimodal structure of precipitation evolves into trimodal structure in the eastern coastal area of Guangdong Province. Under the influence of weak or strong jet stream, the precipitation in the west coast of Guangdong shows bimodal or trimodal structure, while under the influence of class 3 BLJ, it shows a single-peak structure at noon.

• Characteristics and controlling factors of annual soil CO2 emissions and CH4 uptakes from urban turfgrasses in Beijing

  zhangtianli, Yao Zhisheng

  Available online:July 25, 2024  DOI: 10.3878/j.issn.1006-9895.2406.24101

  Abstract(76) HTML(0) PDF(1.68 M)( 688)

  Abstract:With accelerating urban expansion and increasingly growing city population density, urban ecosystems are becoming the hotspots of global climate change. Urban turfgrasses can themselves be a vitally important part of cities, however, its effects on soil-atmosphere exchanges of carbon dioxide (CO2) and methane (CH4) remains unclear. In this study, we performed year-round field measurements of soil respiration (CO2) and CH4 fluxes and associated with environment factors from three typical urban turfgrass turfgrasses (i.e., warm-season turfgrass (WT) dominated by C4 plants species, cool-season turfgrass (CT) and shade-enduring turfgrass (ST), both dominated by C3 plant species) at the Urban Ecosystem National Observation and Research Station, Beijing, using a static opaque chamber method combined with gas chromatography analysis. Our results showed that across the experimental period, soil CO2 emissions or soil CH4 uptakes from all urban turfgrasses exhibited a comparable seasonal pattern, indicating that the seasonality of soil CO2 and CH4 fluxes was significantly affected by different urban turfgrass type. Soil CO2 emissions from urban turfgrasses were positively correlated with soil temperature and soil water content, and their combined effects could explain about 77%-87% of the variations in soil CO2 emissions, In contrast, the variations of soil CH4 uptake were mainly regulated by soil water content, and soil CH4 uptake was negatively correlated with soil water content. Over the annual scale, the cumulative soil CO2 emissions for all urban turfgrasses ranged from 12.1 to 15.2 t C ha-1 yr-1, and annual CH4 uptakes were between 3.71 and 4.27 kg C ha-1 yr-1. Although low temperatures during the non-growing season usually reduce soil CO2 emissions and CH4 uptakes by inhibiting the related microbial activities, our results revealed that total soil CO2 emissions and CH4 uptakes across the non-growing season contributed to 10%-18% and 39%-51% of the annual budgets, respectively, highlighting the importance of measurements spanning the full year. Among the three urban turfgrasses, the WT dominated by C4 plant species showed significantly higher annual soil CO2 emissions but lower annual soil CH4 uptakes as compared to the CT and ST (both of which were dominated by C3 plants species). This was mainly in connection with differences in soil properties and vegetation characteristics between the urban turfgrasses. Overall, our fundings suggest that in the context of various urban turfgrasses being expanding substantially along with rapid urbanization, the efforts of conscious planning and design of C3 related urban turfgrasses may benefit the reduction of soil-atmosphere exchanges of CO2 and CH4, making contribution to mitigating climate change.

• East Asia large scale temperature reversal events and the exploration of its cause in winter

  Li Xueyan, Qi Li

  Available online:July 24, 2024  DOI: 10.3878/j.issn.1006-9895.2310.23105

  Abstract(89) HTML(0) PDF(2.46 M)( 703)

  Abstract:Winter temperatures in East Asia have significant subseasonal oscillation, which have a profound impact on people"s production and life. Based on the reanalysis data of NCEP during the period of 1980–2022, the most typical temperature reversal events in winter of 42 years were found and analyzed in terms of their characteristics and main influencing factors by using correlation analysis, power spectrum analysis, butterworth filter, Plumb wave activity flux analysis and other statistical methods. The results show that: (1) In the winter of 42 years, there are 21 typical "cold-to-warm" events (CTWE) and 6 "warm-to-cold" events (WTCE). In all events, the temperature difference between the warm and cold period was more than 10℃. Besides, the temperature reversal was observed over the whole region. (2) In all events, the geopotential height anomaly in 500hPa over the Ural Mountains has a phase transition 2 days before the reversal of the East Asian temperature. During the WTCE, the anomalous geopotential height of the Ural Mountains changes from negative to positive, 2 days later the temperature anomaly in East Asia changes from warm to cold, and vice versa. (3) Further analysis reveals that during the WTCE, the reversal of the anomalous geopotential height in the Ural Mountains region is closely related to the southern center of NAO. 35 days before the reversal of East Asia temperature, positive geopotential height anomaly has been observed in the southern center of NAO in the stratosphere, then it propagates downward to the troposphere and excites wave flux propagating eastward to the Ural Mountains region, further leading to the anomalous geopotential height in Ural Mountains transition from negative to positive. However, the CTWE is mainly related to the northern center of NAO. Negative geopotential height has existed in the norther center of NAO in the stratosphere 30 days before the reversal of East Asian temperature anomaly. The 30-day leading correlation coefficient between the geopotential height of NAO centers and the corresponding temperature anomaly in different reversal events is as high as -0.8, exceeding 95% confidence level. Therefore, monitoring and prediction of the geopotential height over NAO centers in stratosphere will help us to predict the subseasonal reversal of winter temperature in East Asia 30 days in advance.

• Climatic characteristics of Northeast Cold Vortex and its precipitation during the warm season in Heilongjiang Province

  REN Li, LIU Ying

  Available online:July 24, 2024  DOI: 10.3878/j.issn.1006-9895.2401.23127

  Abstract(145) HTML(0) PDF(1.97 M)( 724)

  Abstract:Based on the hourly precipitation data of 80 national stations in Heilongjiang Province and NCEP/ NCAR reanalysis data, the climatic characteristics of the Northeast cold vortex (NECV) and its precipitation during the warm season (May-September) from 1981 to 2022 were analyzed, and the spatio-temporal distribution characteristics of NECV precipitation in the complex terrain of Heilongjiang Province were studied. The results showed that (1)In Heilongjiang province, the average annual precipitation during the warm season, the precipitation of NECV processes and their proportion in the warm season showed significant interannual and interdecadal variation characteristics. Before 1998, the average annual precipitation in the warm season showed a slow weakening trend, and then an obvious increasing trend. The average annual precipitation of cold vortex processes showed an overall increasing trend. (2)The peak values of precipitation and precipitation frequency were from 14:00 to 17:00. The diurnal variation of precipitation was larger than that of precipitation frequency. The precipitation with greater intensity had more significant diurnal and interannual variation characteristics. (3)The frequency and contribution rate of heavy precipitation were greater in the daytime than at night. The greater the precipitation intensity, the greater the influence on the total precipitation. The contribution of heavy precipitation in the process of NECV was increasing, and the greater the precipitation intensity, the more significant the increasing trend. The contribution of weak precipitation was declining. (4)The spatial distribution of extreme values was closely related to the local topography. The transition area from plain to mountainous area had the largest precipitation extreme value, which was easy to have heavy precipitation, while the precipitation extreme value in mountainous area and plain area was relatively small.

• Interannual Variability of Summer Rainfall in Qinhuangdao-Tangshan Region of North China and its associated with Large-scale Circulation and Sea Surface Temperature Anomalies

  Xiang Liang, Sun Wanyi, Zhang Xiaoxiao, Zhu Congwen

  Available online:July 24, 2024  DOI: 10.3878/j.issn.1006-9895.2312.23112

  Abstract(184) HTML(0) PDF(18.78 M)( 1551)

  Abstract:This paper applied daily observed rainfall data in China, JRA-55 atmospheric reanalysis, ERSST monthly sea surface temperature (SST) data, Pacific decadal oscillation (PDO) and Ni?o3.4 index during 1981–2022, and revealed the dominant circulation regimes and large-scale SST anomalies of summer rainfall anomaly in Qinhuangdao and Tangshan (Qin-Tang region) on interannual time scale based on the EOF, correlation and composite analysis. Our results show the dominant mode of summer rainfall in Qin-Tang region exhibits a consistent variation on the interannual time scale with decreasing rainfall anomalies from north to south. The Mongolian cyclone (MC) and Sea of Japan high (SJH) are the dominant circulation, they both show significantly positive correlation with the summer rainfall anomaly in Qin-Tang region on the interannual time scale. The stronger MC and SJH are conducive to moisture transport, enhance the interaction of warm and cold air mess and extreme summer rainfall anomalies. When SJH is weak, the summer rainfall in this region is extremely less than normal due to the decrease of moisture transport. The negative (positive) phase of Ni?o3.4 index in winter and spring is usually followed by cold (warm) and warm (cold) SST in Indian and northwest Pacific Ocean in summer, which results in the stronger (weaker) SJH and more (less) rainfall in this region. While the positive phase of PDO in spring is often followed by warmer (colder) SST in north (south) of northwest Pacific Ocean in summer, which enhances the MC and the summer rainfall in this region, or vice versa. Therefore, the phase of PDO and Ni?o3.4 in winter to spring possibly provide a useful signal for the following summer rainfall forecast in this region. The results are applicable to the whole North China, which possibly benefits the seasonal forecast of summer rainfall in North China.

• Distribution Properties of Hydrometeor Classification and Supercooled Liquid Water Content for a Typical Precipitating Stratiform Cloud on the Southeastern Tibet Plateau

  Tan Jie, Fu Danhong, Guo Xueliang, Fan Changyuan, Su Debin

  Available online:July 05, 2024  DOI: 10.3878/j.issn.1006-9895.2403.23134

  Abstract(71) HTML(0) PDF(138.21 M)( 854)

  Abstract:The distribution properties of hydrometeor classification and supercooled liquid water content in clouds have important roles in clarifying the microphysical formation mechanisms of clouds and precipitation, as well as establishing and validating cloud microphysical parameterization schemes in numerical models. On basis of Ka?band radar data collected during the Second Tibet Plateau Scientific Expedition in Nyingchi, southeast Tibet Plateau, the distribution properties of hydrometeor classification and supercooled liquid water content for a typical precipitating stratiform cloud on September 16?17, 2019 are investigated after data quality control procedures. The results show that the data denoising rate of the cloud radar based on the “K?nearest neighbor frequency method” is within the range of 1.5 -5.0 %, and the data gap filling rate is within the range of 3.5-7.0%. The difference between the attenuation?corrected radar data and raw data is between 0 and 5 dBZ by applying an iterative correction method. It is found that the precipitation formation mechanism for the typical stratiform cloud in the study region had some unique characteristics. The precipitation was formed by the merging of middle and high clouds induced by lifting of large-scale atmospheric circulation with low?level clouds formed by orographic lifting. In the initial stage, cloud top reached 12 km and the clouds at upper and lower levels were separated distinctly. There was no evident bright band at the melting layer. The particle distribution within the cloud was relatively homogeneous, and ice crystals and snow particles were dominate with a relatively high supercooled liquid water content in the middle and high clouds. In the mature stage, the middle and high clouds merged with the low clouds, leading to precipitation formation and cloud top decrease to be around 10 km. The clouds became inhomogeneous with evident bright band at the melting layer and weak embedded convective cells. The dominant hydrometeors were ice and snow particles, with a small amount of graupel in the embedded convective cells. The supercooled liquid water content was mainly distributed in the embedded convective cells with a maximum value of 0.5?0.6 g m-3. In the decaying stage, as the large?scale weather system passed over the study region, the middle and high cold clouds weakened rapidly, and weak warm rain generated by low?level orographic clouds became dominant, resulting in the disappearance of the bright band at the melting layer. A thin layer of ice and snow was present above the melting layer.

• The role of convection anomalies near the Arabian Sea and South China Sea in regulating extreme high temperatures in the Yangtze River Basin in the summer of 2022

  Ziqian Zheng, Chunhua Shi, Dong Guo

  Available online:July 05, 2024  DOI: 10.3878/j.issn.1006-9895.2405.23168

  Abstract(178) HTML(0) PDF(8.85 M)( 796)

  Abstract:The Yangtze River Basin in July-August 2022 experienced a record-breaking extreme high-temperature event. Using the ERA5 reanalysis data and CN05.1 grid point data, the spectral analysis identifies the low-frequency feature containing 30–64d in this high-temperature event and linear regression showed that the Eurasian subtropical teleconnection and two key Tropical convection activities in the region have an important connection with this high-temperature event. Further analysis using a linear baroclinic model revealed that abnormal convection over the Arabian Sea-Pakistan area and the South China Sea played critical roles in modulating the atmospheric circulation over the Yangtze River Basin at different stages of the heatwave through teleconnection patterns. Specifically, during the positive and negative phases of the low-frequency cycle, enhanced convective activities near the Arabian Sea-Pakistan region modulated the upper tropospheric subtropical Rossby wave train in the north, thereby affecting downstream circulation anomalies over the Yangtze River Basin. Conversely, convective anomalies in the South China Sea initiated Rossby waves that influenced the basin via the Pacific-Japan teleconnection pattern. During the negative phase of low-frequency temperature cycles, weakened convection in the South China Sea predominated, placing the Yangtze River Basin within an anomalous cyclonic circulation with meridional cold advection, leading to cooling in the region. Contrary to the response to the convection in the Arabian Sea, the Yangtze River Basin is located in a cyclonic circulation with abnormal positive vorticity, zonal cold advection promotes cooling in the region; during the positive phase of the low-frequency temperature. the response to the strengthened convection in the South China Sea and the strengthened convection in the Arabian Sea is a synchronous phase, and the Yangtze River basin is located in an anticyclonic circulation with anomalous negative vorticity. At this time, the Yangtze River basin is located on the southerly side within the anticyclonic circulation, the sinking adiabatic motion and meridional warm advection strengthens the positive temperature anomaly in this period. This study elucidates the impact mechanisms of extreme high-temperature events in the Yangtze River Basin and provides insights for forecasting future summer extreme temperature events.

• The observation study of the vertical wind profile in the valley of Mt. Lu using a Doppler wind lidar

  CHEN Yong, DUAN Jing, AN Junling, MA Shupo, ZHANG Xiaopeng, LI Jun

  Available online:June 27, 2024  DOI: 10.3878/j.issn.1006-9895.2404.23162

  Abstract(132) HTML(0) PDF(2.34 M)( 813)

  Abstract:The complexity of valley airflow make the observation of low-level wind profiles and related vertical velocity more important, for the study of mountain cloud-fog physics and the technical guidance of weather modification operation. Based on the valley terrain cloud and fog experiment station (CFS) of Mt. Lu and the height difference between CFS and the meteorological station of Mt. Lu (LS), wind profile observations by a Doppler wind lidar at CFS were operated from November to December 2019. The measurements indicated that there was a good correlation between the 80-m wind speed and direction of CFS and the 10-m wind of LS. The 80-m vertical velocity and horizontal wind speed at the CFS site were mainly between ±0.5ms-1 and 2-4 ms-1, respectively. The average wind speed at the CFS site increased with height, with the wind speed in daytime being lower than that in nighttime. The difference in wind speed between day and night increased with height, with a wind speed difference of -1 ms-1 (-0.2 ms-1) at the height of 80 m (40 m). The vertical movement was mainly related to the direction of the airflow, and the vertical velocity was proportional to the horizontal wind speed. The 80-m southerly wind (112.5o-247.5o) at the CFS site was dominated by upward airflow, while the other wind directions were dominated by downward airflow; and this relationship was extended to 260m from 80m. The weak wind shear of low-level airflow at the CFS site can lead to vertical motion stratification, indicating more complexity of airflow in the mountainous terrain than that of the plain.

• Precipitation division and circulation characteristics during the flood season in Hunan, Jiangxi, Zhejiang and Fujian

  ZHOU Fang, WANG Donghai, WEI Junhong

  Available online:June 24, 2024  DOI: 10.3878/j.issn.1006-9895.2404.23159

  Abstract(269) HTML(0) PDF(7.27 M)( 775)

  Abstract:The Hunan, Jiangxi, Zhejiang and Fujian regions (hereafter referred to as XGZM) correspond to one of the areas where precipitation begins earliest in China. They have experienced the pre-flood period in South China, the Meiyu period in the Yangtze and Huai River valley, and the post-flood period in South China. The precipitation is highly concentrated, but the precipitation and circulation characteristics are different from the other counterparts. In order to study the basic characteristics of precipitation during the flood season in XGZM, this paper uses the ground meteorological observation stations and ERA5 reanalysis data to first compare the characteristics of precipitation over XGZM in different monsoon rain periods, and then analyze its evolution characteristics by each pentad. Finally, a new way of classifying the flood season based was proposed based on the daily precipitation and the number of heavy precipitation stations on rainy days. The flood season and the different stages of the flood season were defined according to the new method. The precipitation characteristics before and after the flood season and at different stages of the flood season, as well as the evolution characteristics of background circulation, were explored. The study shows that: (1) Compared with other segmentation methods, the new definition method can better describe the evolution characteristics of the north-south displacement of the heavy rain belt and the east-west change of the rainy center during the flood season in XGZM. (2) The flood season in XGZM has its own unique precipitation characteristics that are different from the pre-flood season in South China and the Meiyu period in Yangtze and Huai River Valley. On average, the flood season in XGZM starts at the 22nd pentad and ends at the 50th pentad. It can be divided into three stages: the spring rainy season, the main flood season, and the post-flood season, among which the main flood season can be divided into the early stage of the main flood season and the peak stage of the main flood season. The onset of the spring rainy season (i.e., the first stage) is latter than the pre-flood season in South China. The overall distribution of precipitation in the spring rainy season is relatively even, with two heavy rain bands in the southern part of Nanling Mountain area and northern part of Jiangxi and Hunan. The main flood season (i.e., the second stage) begins and ends earlier than the Meiyu period in Yangtze and Huai River valley. The precipitation in the main flood season is enhanced comprehensively, with the center of heavy precipitation located from the plain of Poyang Lake to Wuyi Mountain area. The post-flood season (i.e., the third stage) starts later than the post-flood season in South China. The precipitation in the post-flood season is mainly located in the coastal areas of southeastern Fujian. (3) After entering the flood season, the atmospheric circulation in XGZM has changed significantly. The atmospheric circulation characteristics associated with the beginning of the flood season are mainly as follows: (a) the South Asian high pressure moves northward over the plateau, (b) the westerly airflow over XGZM area weakens, (c) the subtropical high pressure rises northward, (d) the ridge is located at 18-21°N, (e) the low-altitude southwest jet stream and the ultra-low altitude southerly jet stream are both established and strengthened, and (f) the moisture transport is greatly increased. These characteristics are different from those of the pre-flood period in South China and the Meiyu period in Yangtze and Huai River valley. The evolution of the circulation at different stages of the flood season is mainly reflected in the positions of the trough and the subtropical high, the strength of the low-level wind speed and the displacement of the low-level wind speed convergence zone, etc. These results help us better understand the spatiotemporal distribution characteristics and generation mechanism of the flood season precipitation over XGZM.

• The impacts of different-scale initial errors on the track and intensity simulated-forecasts of typhoon In-fa (2021)

  周菲凡, ZHANG HAN

  Available online:June 24, 2024  DOI: 10.3878/j.issn.1006-9895.2405.24023

  Abstract(70) HTML(0) PDF(3.41 M)( 808)

  Abstract:A long-lived tropical cyclone that occurred on North West Pacific called In-fa has been studied. Two kinds of data, one is ERA-5, another is FNL are used to produce the initial values for model integration. The ERA-5 data is taken as reference, the difference between FNL and ERA-5 is taken as perturbation. By decomposing the perturbation into different kind of scales, we reveal the impacts of different-scale initial perturbations on the forecasts of tropical cyclone. The results indicate that, whether it is intensity forecasting or track forecasting, the impact of mesoscale errors is most significant in the first ten days of forecasting. After adding mesoscale errors, the typhoon track tends to add up all the errors, and the intensity also tends to add up all the errors, indicating that mesoscale errors played a decisive role in the forecast for the first ten days. In the next four days of forecasting, the contributions of large-scale and small-scale errors gradually become prominent, and the effects of the three scale errors are equivalent. In addition, mesoscale errors in the early stage caused the typhoon track to be eastward and stronger, while large and small scale errors caused the typhoon track to be westward and weaker. The analysis of the reasons shows that the mesoscale error field has a higher similarity with the entire error field, that is, the information of the entire error field is mainly reflected in the mesoscale error, so the role of mesoscale error in the early stage is significant. In addition, the superimposed mesoscale error field has a stronger initial strength for the background wind, and the eastward track results in a later landing time. Therefore, mesoscale error leads to a stronger typhoon intensity. However, due to the large and small scale errors causing the typhoon track to be westward and make landfall earlier, the overall strength of the typhoon is weaker.

• Predictability Analysis and Error Growth Characteristics of a Warm-sector Rainstorm of Southern China

  WEI Jinfeng, SUN Lu, SHI Yang, WANG Qiuping, MA Xulin

  Available online:May 22, 2024  DOI: 10.3878/j.issn.1006-9895.2402.23166

  Abstract(66) HTML(0) PDF(4.59 M)( 842)

  Abstract:Due to the influence of weak synoptic systems, the relatively weak precursor signals make significant challenges for the forecast of warm-sector rainstorms in southern China. In order to explore the predictability of warm-sector rainstorms in southern China, and further investigate the error growth characteristics of warm-sector rainstorms at different scales, high-resolution ensemble forecast experiments based on the WRF mesoscale numerical prediction model is carried out for a double rainbands precipitation event that occurred in Guangdong province on 30-31 May 2021. The experimental results show that the convergence of strong low-level wind speed is the main convection initiation conditions for this warm-sector rainstorm of southern China, the mesoscale convergence line at the sea-land interface in South China and the strong southwestern boundary layer jet are conducive to promoting convection. The magnitude of forecast errors and their growth rates at different spatial scales in the warm-sector rainstorm are significantly different, and this rainstorm event is less sensitive to small variations in initial perturbation amplitudes. After convection initiation, the error growth exhibits more obvious nonlinear characteristics, the small-scale errors grow rapidly in the form of “upscale error growth” until saturation, and then dominated by mesoscale error growth. The above study shows that the predictability of warm-sector rainstorms in southern China is limited by multiple factors, and the moist convective process can accelerate the growth of mesoscale forecast errors. Moreover, the strong nonlinear characteristics of forecast error growth at different scales in synoptic systems directly limit the predictability.

• Assimilation Application of Multi-band Dual-Radar Retrieval Winds in the Forecast of a Rainstorm Event in Southwest China

  Wang Yehong, ZHAO Yuchun, LUO Changrong, HE Guangbi

  Available online:May 22, 2024  DOI: 10.3878/j.issn.1006-9895.2405.23137

  Abstract(58) HTML(0) PDF(191.94 M)( 779)

  Abstract:With radial wind data from 18 CINRAD/S and CINRAD/C radars in southwest China, the S-S, C-C, and C-S dual-radar wind field are retrieved and a mosaic of them is made using three-dimensional dual-radar wind retrieving technique considering standard atmospheric refraction in the dynamic earth coordinate. Then eight cloud-resolving scale numerical experiments were conducted with the WRF4.2 model and the WRFDA assimilation system to simulate a rainstorm event in southwest China on July 6-7, 2017 and investigate the impact of three-dimensional variational assimilation of dual-radar retrieved wind with different horizontal resolutions upon the heavy rainfall forecast. The results are as follows. (1) The dual-radar retrieving technique of three-dimensional winds in the dynamic earth coordinate considering the standard atmospheric refraction can be well applied in dual-radar wind retrieving of different-band radars in southwest China. (2) As to the heavy rain band from northeast Sichuan to north Chongqing, eight retrieval-wind assimilation experiments with different horizontal resolutions all significantly improved the direction, precipitation area, range, location and intensity of the heavy rain band and is more close to the real situation than the control experiment. The spatial correlation coefficient and TS score of the 24-hour accumulated precipitation at 06-30 hours valid time are significantly increased with the missing and false forecasting rates both decreased. The improvement is best for the rainfall equal to and greater than 25 and 50 mm. The forecast of wind-field assimilation experiment with a horizontal resolution of 0.25 ° is the best, where an appropriate analysis increment field relative to the background wind field is generated under the assimilation of appropriate resolution wind-field data and the analysis wind field are more close to the real. The wind field structure in the control experiment are continuously corrected in the model integration and resulted in the simulated flow field structures such as vortices, shear lines, high-altitude troughs, wind direction and wind speed being closer to the real situation. (3) As to the heavy rain band from northern Yunnan and southern Sichuan to northwestern Jiangxi, the assimilation of retrieved winds with a resolution of 0.15 ° or higher has a significant negative impact on the prediction results. The negative impacting becomes more significant when the resolution of retrieval wind increases. This is due to the data correlation caused by the assimilation of overly dense retrieval winds. The analyzed incremental fields are falsely and excessively high and ultimately affect the simulated wind field structure and the rain-band position. (4) The assimilation of retrieval wind with different horizontal resolutions has a significant impact on numerical prediction results. Overall, a horizontal resolution of 0.2 ° is the critical threshold for the thinning scheme of retrieved winds in this study, with the condition using a triply nested domain with resolutions of 18/6/2 km and conducting data assimilation in all domains. When the horizontal resolution of the retrieval wind is not higher than this threshold, it often has a positive impact on the prediction results, with a horizontal resolution of 0.25 ° being the best thinning scheme.

• Effect of less sea ice in the Barents Sea on anticyclone activity in Siberia

  Lu Chuhan, Xia Ping, Zhang Yumin, XinFei

  Available online:April 29, 2024  DOI: 10.3878/j.issn.1006-9895.2403.23123

  Abstract(106) HTML(0) PDF(1.51 M)( 890)

  Abstract:In the context of global warming, the Arctic region has warmed significantly and sea ice has retreated dramatically, and previous studies have revealed that the sea ice condition in the Barents Sea region in autumn is a significant precursor factor for temperature anomalies in Eurasia in late winter, while the activity of the low-level anticyclone in Siberia in winter is closely related to the change of the cold air, but whether and how the Arctic sea ice affects the activity of low-level anticyclone/cold high-pressure in winter in Siberia is still to be Further studies are needed. In this paper, the effects and pathways of low sea ice in autumn in the Barents Sea region on anticyclone activities in Siberia are investigated using the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data, ERA5, and sea ice data. The results show that: (1) the interannual variations of the fall sea-ice density in the Barents Sea region have an effect on both winter anticyclones and the quality of the cold air they carry in the Siberian region, and the anticyclone activity is enhanced and the cold air it carries is increased when there is less sea-ice in the fall. (2) Reduced sea ice area in the fall will lead to more ocean heat transfer to the atmosphere in the late season, thus reducing the meridional temperature gradient between the polar regions and the mid-latitudes in winter, and thus weakening the mid-latitude westerly winds, resulting in enhanced anticyclone activity in Eurasia. (3) Using the atmospheric circulation model CAM6, we designed a sensitivity test for sea ice changes in the Barents Sea region, and the results also reproduced that under conditions of low sea ice, most of the Eurasian continent, except for the area east of Lake Baikal and northeastern China, showed an increase in anticyclone frequency and an enhancement of the central pressure of the anticyclone. In particular, the reduction of sea ice caused a significant decrease in the meridional gradient of the vortex, which led to an increase in the frequency of blockages in the East European Plain, the Ural Mountains, and East Asia, resulting in an increase in anticyclone activity and a decrease in temperature in most of the mid-latitude regions of the Eurasian continent.

• Consistency of interannual variability of convection Maritime Continent during the boreal spring and the possible effects of tropical SST

  Dong Xinyu, Shi Xiaohui, Wen Min

  Available online:April 19, 2024  DOI: 10.3878/j.issn.1006-9895.2404.23124

  Abstract(70) HTML(0) PDF(10.34 M)( 870)

  Abstract:The seasonal transition of the convective (STC) in the Maritime Continent (MC) during the boreal spring can largely influence the establishment of the Asian summer monsoon, but the interannual variability of STC in MC and its causes are still not well understood. In this paper, based on the climatic characteristics of STC in MC, we define some characteristic indicators of convection and circulation, further analyze the interannual variation characteristics of STC in MC, and explore the possible effects of sea surface temperature anomalies (SSTA) in the tropics and their mechanisms. The results show that the interannual variabilities of STC in MC and the evolution of atmospheric circulation over the surrounding areas have an overall consistency, and are mainly regulated by the El Ni?o ? South Oscillation (ENSO) events. In some special years, the distribution of the SSTA in the eastern tropical Indian ocean could stimulate an anomalous local atmospheric circulation, which will ultimately lead to some changes on the convective activity in MC.

• Effects of sea-land thermal differences over East Asia-Pacific and Europe-Atlantic regions on mean and variability of summer precipitation in China

  NING Ke, ZHANG Jie, WU Bin

  Available online:April 19, 2024  DOI: 10.3878/j.issn.1006-9895.2404.23129

  Abstract(130) HTML(0) PDF(31.03 M)( 828)

  Abstract:The summer precipitation in China is mainly affected by the East Asian summer monsoon, and the main factor affecting the monsoon is the land-sea thermal contrast. Based on the ECMWF / ERA5 reanalysis data and CN05.1 gridded precipitation data set from 1979 to 2022, this paper defines the European-Atlantic land-sea thermal contrast and two types of East Asian-Pacific land-sea thermal contrast: East Asia-North Pacific and East Asia-Subtropical High land-sea thermal contrast. The characteristics of three land-sea thermal contrast and the spatial and temporal characteristics of summer precipitation in China are studied, and the effects of land-sea thermal contrast on the mean and variability of summer precipitation in China and the influence of variability on extreme precipitation are analyzed. The results show that: (1) The precipitation in Northeast China, the lower reaches of the Yangtze River and the Tibet Plateau is significantly affected by the land-sea thermal contrast. The mean and variability of summer precipitation in these areas are increasing, and the increase of variability increases the probability of extreme precipitation in these areas. (2) The land-sea thermal contrast between East Asia-Pacific and Europe-Atlantic has maintained an increasing trend over the past 40 years and has shown an increasing trend under the medium emission scenario, and the land surface warming is higher than that of the ocean. (3) The main contribution of precipitation generation and change in Northeast China is the land-sea thermal contrast between East Asia-Pacific and East Asia-Subtropical High. The main contribution to the precipitation in the lower reaches of the Yangtze River is the land-sea thermal contrast between East Asia and the Pacific. The main impact on precipitation in the plateau area is the thermal contrast between East Asia-subtropical high and Europe-Atlantic sea and land. Finally, the results of LBM simulation further confirm that the Euro-Atlantic thermal contrast increases the precipitation in the western plateau and decreases the precipitation in the eastern plateau. These findings provide an important basis for us to understand the temporal and spatial variation of summer precipitation in China and the physical mechanism behind it.

• The interaction between tilted ridge-trough systems and transient waves and their impact on extreme low-temperatures in the arid and semi-arid regions of China

  Li Yan, Xie Zuowei, Ding Min, Bueh Cholaw, 王月

  Available online:April 17, 2024  DOI: 10.3878/j.issn.1006-9895.2404.23141

  Abstract(87) HTML(0) PDF(5.62 M)( 894)

  Abstract:This paper used the ERA5 reanalysis data to investigate the atmospheric circulation configurations and their evolution processes for three types of extreme low temperature events in the arid and semi-arid regions of China (dryland for brevity) during the winter half-year. This study examined the activity characteristics of transient eddies under different circulation configurations and their feedback forcing to the abnormal circulation. The results showed that the continuous amplification of tilted ridge and trough over the Eurasian continent was the key reason for extreme low temperature events in the dryland. This pair of ridge and trough was primarily maintained by the incoming low-frequency Rossby wave energy. Under its influence, transient eddies were abnormally active on the southern and northern sides of the titled ridge and trough, in which transient eddies in the south of trough guided part of cold air masses southward and further intensified the extreme low temperature events. In addition, the convergence and divergence of transient vorticity fluxes favored the continuous maintenance of tilt ridge and trough, which was conducive to amplification and eastward expansion of the low-level Siberian cold high pressure, and thus led to extreme low temperatures affecting the entire dryland. When the tilted ridge and trough were elongated longitudinally, the ridge over the Ural Mountain weakened and moved eastward as Rossby wave energy emitting downward. Correspondingly, the low-level Siberian cold high pressure also exhibited an eastward displacement, and the activity of transient waves was suppressed. The extreme low temperatures are mainly confined to the eastern dryland.

• Using Surface-grid Nudging to Improve Numerical Prediction of Warm-sector Heavy Rainfall Over South China During Pre-summer Rainy Season

  Zheng Yuhao, Yin Jinfang, 李丰

  Available online:April 15, 2024  DOI: 10.3878/j.issn.1006-9895.2401.23072

  Abstract(86) HTML(0) PDF(3.46 M)( 872)

  Abstract:Significant uncertainties exist in the ability of numerical models to reproduce heavy rainfall events over warm sector during the pre-summer rainy season in southern China. One such event occurred with heavy rainfall along the coastal line of Guangdong Province during the period of 29–30 May 2020, and all operational numerical models failed to predict this event at that time. Consequently, eight experiments were conducted to assess the influence of nudging surface-intensive observations into the numerical simulations. The findings reveal that nudging all surface meteorological elements, in what is termed the control experiment (EXP1), reproduces well the development of linear convection and the spatial and temporal evolution of heavy precipitation along the coastline of Guangdong Province. Sensitivity experiments focusing on nudging different surface elements indicate that nudging surface water vapor plays a pivotal role in convection initiation, primarily attributed to the swift escalation of relative humidity from 80% to near saturation (99%) within 3 hours in the low levels, accompanied by a marked reduction in convective inhibition (CIN), lifting condensation level (LCL), and level of free convection (LFC). Nudging surface temperature accentuates thermal buoyancy by amplifying potential temperature perturbations, thereby influencing the initiation and organization of convection. The occurrence and development of convection are considerably delayed in the absence of the nudging surface temperature, and its organization is less structured. Nudging surface wind helps to correct the near-surface southwesterly wind direction, aligning the convection evolution and the rainfall more closely with the observations. Additional six sensitivity experiments were carried out to further explore the impact of nudging duration on simulations. The results suggest that nudging all surface meteorological elements for 6 hours mirrors the outcomes of the control run, effectively reproducing well the heavy rainfall along the coastline. Despite a swift rise in water vapor within the initial 3 hours, the maintenance of water vapor for a certain time (another 3 hours) promotes rapid convection development. Thus, the numerical prediction performance of heavy rainfall in the warm sector over southern China can be improved to a certain extent by nudging surface intensive observations using the surface-grid nudging technique during the initial several (6) hours of model integration.

• Response of Eastern China Summer Rainfall Modes to Increased Carbon Dioxide

  DUAN YAWEN, YANG QING, MA ZHUGUO, ZHENG ZIYAN, LI MINGXING

  Available online:April 09, 2024  DOI: 10.3878/j.issn.1006-9895.2304.23062

  Abstract(217) HTML(0) PDF(2.40 M)( 945)

  Abstract:The spatial distribution of summer rainfall anomalies over eastern China often characterized by meridionally banded structure. The possible change of it in response to global warming is of great significance to water resource management and disaster prevention. Previous studies show critical role of climate variability on modulating these rainfall modes while seldom studies considered model’s internal variability on investigating their responses to increased greenhouse gas. Based on model simulations with different forcings from the fifth Coupled Model Inter-comparison Project (CMIP5), this paper analyzes the response of the leading modes of eastern China summer rainfall to increased CO2 concentration with consideration of model internal variability. The results show that increased CO2 would not change the leading modes of eastern China summer rainfall. The tripole and dipole mode during the recent decades would still be the leading modes in the abrupt quadruple CO2 experiment (4×CO2) and 1% per year increased until quadrupled CO2 experiment (1%CO2) with the dipole mode plays a more dominant role. However, the frequency, intensity and trend of these modes will change. Compared to pre-industrial control simulation (piControl), the temporal variability of the tripole and dipople mode both decrease under 4×CO2 forcing. The variability of dipole mode intensifies while tripole mode weakens under 1%CO2 forcing. With the gradually accumulation of CO2, the occurrence of the positive and negative phase of these modes will change. The phase of tripole mode which featured with drought over the Yangtze River Basin while flood over North and South China would happen more frequently. So does the “Southern flood and northern drought” phase of the dipole mode. Compared to piControl simulation, the sea surface temperature and atmospheric circulation anomalies associated with the dipole and tripole mode both weaken under 4×CO2 forcing. Whereas under 1%CO2 forcing, their differences are regional dependent. The tripole mode is associated with weakened anomalies over the Indian and western North Pacific Ocean while the dipole mode is associated with stronger central and eastern tropical Pacific and North Pacific sea surface temperature anomalies.

• Rapid Intensification typhoon with“Atypical Convection”: The Role of Surface Latent Heat Flux

  shenshangqi, huangqijun, gexuyang

  Available online:April 09, 2024  DOI: 10.3878/j.issn.1006-9895.2310.23073

  Abstract(88) HTML(0) PDF(6.36 M)( 1096)

  Abstract:In this study, rapidly intensifying (RI) tropical cyclones (TCs) with ‘Atypical’ convection in the Northwest Pacific were screened by using reanalysis data and infrared cloud images. A group of slow-intensifying (noRI) typhoons with ‘Typical’ convection were gathered for comparison. It is found that the RI group has a stronger maximum region of surface latent heat flux on the left side of the vertical wind shear (VWS) direction. To further explore possible mechanisms, the ‘Atypical’ convection case ‘Lekima’ (2019) was selected for sensitivity numerical experiments. The diagnostic results indicate that the surface latent heat flux on the left side of the VWS direction helps establish convective-instability in the region. Consequently, the effect of the "Ventilation effect" was weaken through the "Boundary layer entropy recovery" mechanism caused by the surface latent heat flux. Under easterly VWS, convection activity can be enhanced in high surface latent heat flux regions during the transition from the down-shear to the up-shear, thereby stimulating strong upper outflow channels. The establishment of outflow channels (Outflow blocking mechanism) can resist the environmental easterly flow, which weakening the strength of VWS, and allowing the typhoon to develop vertically.

• Comparative Study on the Statistical Characteristics of Raindrop Spectral Distribution of Five Types of Weather Circulation Precipitation in Shaanxi Flood Season

  Hu Qiyuan, QIN Zhangcai, QI Youcun, ZHU Ziwei, FENG Dian, ZHANG Li

  Available online:April 09, 2024  DOI: 10.3878/j.issn.1006-9895.2403.23117

  Abstract(67) HTML(0) PDF(2.63 M)( 997)

  Abstract:The raindrop spectrum, as a high-frequency observation data that directly describes the characteristics of raindrop size and quantity, has been widely used in the fine evaluation and analysis of raindrop changes in different weather conditions and types. The study utilized raindrop spectrum observation data from 2019 to 2022 in the Shaanxi Province. We have analyzed the overall characteristics of precipitation under the influence of five weather circulations, the drop spectra characteristics of rainstorm and non-rainstorm processes, and the drop spectra characteristics of convective precipitation and stratiform precipitation. The results indicate that the contribution of precipitation with rainfall rate>5mm h-1 to the total rainfall of the process varies significantly among different circulation systems. The main reason for this situation is the difference in the number concentration and contribution of raindrops in each diameter intervals. For example, the southwest airflow type is often characterized by stable precipitation formed by long-term high concentration small raindrops, while the northwest airflow type is characterized by strong precipitation formed by short-term high concentration large raindrops. The characteristics difference of drop spectrum between different circulation rainstorm and non-rainstorm further increase, and heavy rainfall have a significant promoting effect on raindrop spectral parameters. From the variation of number concentration with diameter, the number proportion and diameter spectral width of convective precipitation raindrops with rainfall rate>5mm h-1 in the rainstorm are generally higher than those of non-rainstorm. The distribution range and magnitude of Dm-Nw between convective precipitation and stratiform precipitation are nearly similar, with differences in the location of mean and high value areas. Compared with similar regions such as Zhaosu, Zhuhai, and Palau Island, most of convective precipitation in Shaanxi tends to have oceanic convective precipitation characteristics. A few continental convective precipitation occur in flat straight airflow weather or northwest airflow weather. Based on the above analysis, this study differs from the traditional Z-R empirical relationship and optimizes the fitting of Z-R precipitation estimation equations for various circulation precipitation based on raindrop spectra, which helps to improve the accuracy of radar precipitation estimation in different weather scenarios in the local area in Shaanxi.

• Effects of 10-30-day Atmospheric Low Frequency Oscillations at Mid-High Latitudes and Low Latitudes on Summer Precipitation in China

  Guo Ziyi, Huang Qian, Yao Suxiang

  Available online:April 07, 2024  DOI: 10.3878/j.issn.1006-9895.2402.23126

  Abstract(71) HTML(0) PDF(5.79 M)( 845)

  Abstract:Atmospheric low frequency oscillations are closely related to summer precipitation and related catastrophic weather in China, and it is of great significance to study the effects of 10-30-day low frequency oscillations on weather and climate. In this paper, the effects and mechanisms of the 10-30-day oscillations at mid-high latitudes and low latitudes on the average summer precipitation in China during the period 1991-2020 are investigated by using station observations data and ERA5 reanalysis data, etc. According to the singular value decomposition(SVD) analysis, the 10-30-day oscillations at mid-high latitude are closely related to the spatial distribution of inverse-phase precipitation over Yangtze River and South China Sea, When the 10-30-day oscillations in north of Lake Baikal are weak and the oscillations in south of Lake Baikal are strong, the precipitation exhibits a significant decrease in the Yangtze River basin while showing a notable increase from the South China Sea to South China; The key region of the low latitudes 10-30-day oscillations is located in the northwestern Pacific, where precipitation in southern China exhibits a significant positive anomaly during periods of strong oscillation within this region. The 10-30-day oscillations at mid-high latitudes mainly affect the mean position of the summer subtropical westerly jet stream through wave-current interactions, which makes the position of the secondary circulation near the jet stream to be anomalous, thus indirectly affecting the precipitation in the Yangtze River Basin and the South China Sea to South China, and making it show anomalous inverse-phase distributions; Distinguishing it from the mid-high latitudes, the 10-30-day oscillations at low latitudes over northwest Pacific propagate northwestward to southern China, directly inducing precipitation anomalies.

• Vertical Structure Analysis of Cold Vortex over Northeast China Based on Multisource Data

  LI Yao, ZHANG Tiening, ZHAO Shuhui, SUN Li, ZHAI Qingfei

  Available online:April 07, 2024  DOI: 10.3878/j.issn.1006-9895.2312.23095

  Abstract(193) HTML(0) PDF(2.90 M)( 884)

  Abstract:In order to study the vertical structure of precipitation in the northeast cold vortex cloud system further, this paper analyzes the microphysical characteristics of the three northeast cold vortex rainfall weather processes in Fumeng County since 2020 by using the micro-rain radar and laser raindrop spectrometer deployed in the national ground observation station of Fuxin Mongol Autonomous County, Liaoning Province. The results show:in the cases dominated by stable precipitation of Stratus clouds, the raindrop spectra measured by the micro rain radar and the raindrop spectrometer have a good consistency, while in the cases with more convective precipitation. The average raindrop spectrum observed by the micro rain radar and the raindrop spectrometer only shows good consistency in the medium particle segment (1-2.5mm); in the stratus precipitation stage, the smaller ice crystal particles begin to melt faster through the 0℃ layer, and the small cloud droplets accumulate below the 0℃ layer, and several concentrations of extreme values appear, below the extreme value, the larger ice crystal particles experience a longer melting distance and become larger raindrops, at the same time, the accumulation of small cloud drops further promotes the collection and collision effect of large cloud droplets, which is conducive to the formation of large raindrops, and a spectral width extreme value appears below the zero degree layer, which is manifested as a vertical raindrop spectrum "Bulge", "Bulge" occurs within 2-3 minutes from the onset to the fall. The "bulge" can be seen as the intuitive performance of the bright band promoting precipitation in the stratus precipitation stage, but whether this promotion of precipitation can bring a significant increase in rainfall intensity on the ground depends on the water vapor content in the near-ground atmosphere, which is manifested in western Liaoning, in dry spring, the relative humidity of the atmosphere is low, and the bright band does not help the broadening of the raindrop spectrum on the ground, but in the summer when the water vapor is relatively abundant, the downward movement of the "Bulge" to a certain extent leads to the widening of the near-ground raindrop spectrum and the increase of rain intensity; Compared with other regions, the precipitation concentration in western Liaoning is small, but the average concentration of stratus precipitation and convective precipitation is not much different, and the difference in mass-weighted diameter leads to the difference in rain intensity.

• Characteristics of the East Asian subtropical westerly jet"s zonal oscillation during the Mei-yu period

  ZHENG Qidan, ZHANG Yaocun

  Available online:April 03, 2024  DOI: 10.3878/j.issn.1006-9895.2403.23106

  Abstract(69) HTML(0) PDF(8.52 M)( 963)

  Abstract:Based on the EAR5 daily reanalysis data and observational precipitation data at 2437 stations in China from 1979 to 2020, this study analyzes the zonal oscillation characteristics of the East Asian subtropical westerly jet and its relationship with the East Asian atmospheric circulation and precipitation during the Mei-yu period. The results reveal that there are two intensity and position variation types for the East Asian subtropical westerly jet during Mei-yu period by comparing the 200 hPa regional mean zonal wind anomalies in a large value area of standard deviation (37o-47oN, 100o-120oE) with the two jet stream centers over the Western Pacific (37o-47oN, 140o-160oE) and the Tibetan Plateau (37o-47oN, 80o-100oE). For the first type, the jet stream center is situated over the western Pacific Ocean in the early stage, then the intensity of the jet stream over the western Pacific weakens, and an enhanced jet stream center appears on the western side of the jet stream. The maximum zonal wind shows a rapid westward migration feature, which is called the rapid westward migration type. For the second type, the jet stream center is located over the Tibetan plateau in the early stage, then steadily strengthens and moves eastward. The maximum zonal wind exhibits a gradual eastward migration feature, which is referred to as the gradual eastward migration type. The analyses of circulation and precipitation corresponding to the two jet stream oscillation types indicate that, with the rapid westward migration of the jet stream, the east ridge point of the South Asian High is located to the east, and the western Pacific Subtropical High’s intensity is increased and moved to the west, and the circulation pattern in the middle and high latitudes is characterized as "two troughs and one ridge". Furthermore, as the meridional increase of 200 hPa divergence and the 700 hPa water vapor transport rises to the north, the position of the rain belt shifts from south to north. Corresponding to the gradual eastward migration type, the east ridge point of the South Asian High is located to the west, and the western Pacific Subtropical High’s intensity is decreased and contracted to the east, the circulation pattern in the middle and high latitudes is featured as "two ridges and one trough," and the blocking highs occur more frequently over the Okhotsk Sea region. Meanwhile, the upper-level divergence in the lower reaches of the Yangtze River weakens, while the upper-level divergence and lower-level water vapor transport strengthen in the upper reaches of the Yangtze River, thus forming an antiphase change in precipitation intensity between the upper and lower reaches of the Yangtze River.

• Characteristics of Aerosol Size Distribution and Cloud Condensation Nuclei Activation During the Summer in The Mountain Tianshans

  WU ZIHAO, LIU ANKANG, WANG HONGLEI

  Available online:January 16, 2024  DOI: 10.3878/j.issn.1006-9895.2309.23040

  Abstract(170) HTML(0) PDF(5.59 M)( 1473)

  Abstract:To analyze the characteristics of cloud condensation nodules (CCN) and aerosol particle size distribution and their influencing factors in the Middle Tianshan region of Xinjiang, aerosol and CCN number concentration data were measured using an aerosol wide-range particle size spectrometer and a Cloud Condensation Nodule Counter from August 4–25, 2019, and combined with meteorological element data and the HYSPLIT model for comprehensive analysis. The results show that during the observation period, the mean value of aerosol number concentration in Tianshan was 3607±4105cm-3, with the highest percentage of Aegean nuclear mode particles (64.76%). The mean values of CCN number concentration at 0.1%, 0.2%, 0.4%, 0.6% and 0.8% supersaturation were 185±185cm-3, 648±345cm-3,1576±1045cm-3, 2077±1417cm-3 and 2408±1657cm-3, respectively. The average spectral distribution of aerosol number concentration showed a unimodal distribution with peak particle size located at 29.5 nm. The diurnal variation of aerosol number concentration peaked at 08:00 (Beijing Time, the same below), 17:00 and 20:00, which was mainly affected by the diurnal variation of boundary-layer height, mountain-valley wind, emission sources, and other factors. The aerosol particles in the Tianshan mountains during summer were found to exhibit different modes of distribution. The Aitken mode particles displayed a bimodal distribution, while the accumulation mode particles had a trimodal distribution. The number concentration of nuclear mode particles showed a unimodal diurnal variation, which may be attributed to new particle formation. The CCN activation spectrum fitting result is N=3111S0.896 (N is the CCN number concentration at the supersaturation S), which is a clean continental type feature. The diurnal variation of CCN number concentration peaked at 08:00, 18:00 and 21:00. New particle formation (NPF) is beneficial to the increase of CCN number concentration at the mountain Tianshan. Under the supersaturation of 0.1%, 0.2%, 0.4%, 0.6% and 0.8%, the average concentration of CCN in NPF day is 13%, 18%, 25%, 22% and 20% higher than that in the non-NPF day, respectively. The relative humidity (RH) has a greater impact on the concentration of nucleation mode particles and a smaller impact on the concentration of other mode particles. As RH increases, the aerosol size distribution shifts towards larger particle sizes. When RH>60%, the number concentration of aerosol and CCN decreased with increasing RH. The aerosol and CCN number concentrations are higher under northerly and easterly winds due to the influence of topography and valley winds. There are four main types of air masses in Tianshan: western (29.2%), northwestern (29.3%), northeastern (27.0%), and southern (14.5%). The aerosol number concentration of the northeastern air mass from the northern Tianshan Mountains is the highest at 5449±3793cm-3 and the lowest at 1971±2087cm-3 due to the different direction and movement path of the air masses and the influence of the northern urban zone. The northeastern air mass has higher CCN number concentrations at all supersaturation levels, which are 100%-150% higher than the lowest southern air mass.

• Study on the spatio-temporal distribution of land lightning and related meteorological factors in China

  YAN Jinlei, ZHAO Yang, TUO Yufeng, KONG Xiangzhen, BI Lixia

  Available online:December 26, 2023  DOI: 10.3878/j.issn.1006-9895.2308.23048

  Abstract(101) HTML(0) PDF(14.37 M)( 1186)

  Abstract:Medium Range Weather Forecasts, were used to study lightning in different regions of mainland China. The relationship between lightning and convective available potential energy (CAPE), precipitation (P), convective inhibition (CIN) and relative humidity (RH) was analyzed from the spatial and temporal distribution and quantitative relationship. The results show that lightning has a good correlation with CAPE, P and CAPE×P in time and space. An appropriately small CIN and a sufficiently large CAPE are most conducive to generating lightning; The higher the CAPE, the more lightning; The smaller the inhibition energy is, the more likely it is to convection and further generate lightning. However, CIN should not be too small, because too small CIN will lead to less lightning. A low CIN value is not sufficient for lightning to occur, and the relative humidity needs to be high. Lightning activity is concentrated in the environment where RH is 60%~90%. If RH continues to increase, lightning activity will decrease. Even in high CIN conditions, with certain moisture and CAPE conditions, there can be a lot of lightning.

• A review on the extinction contribution of aerosol components in United States and China

  Xin Jinyuan

  Available online:December 26, 2023  DOI: 10.3878/j.issn.1006-9895.2312.23316

  Abstract(249) HTML(0) PDF(2.12 M)( 1036)

  Abstract:Aerosol excintion is the main factor affecting atmospheric visibility. The nonlinear relationship between aerosol concentration and scattering and absorption characteristics leads to great uncertainty in the influence of aerosol on the visibility. The concentrations of reconstructed fine mass (RCFM) ranged from 1.4 to 19.4 μg m–3 and reconstructed aerosol extinction coefficients from 10.0 to 172.5 Mm–1 in the United States from 1988 to 2008 from IMPROVE (the Interagency Monitoring of Protected Visual Environments) network. The average fine particulate matter (PM2.5) concentrations in various regions of China ranged from 14.3 to 188.3 μg m–3 from 2006 to 2018, corresponding to reconstructed extinction coefficients of 52.6–1044.0 Mm–1. The PM2.5 concentration in the U.S. region was comparable to that of Sanya, China. In most cases, sulfate was the largest contributing component to aerosol extinction, accounting for up to 77%, followed by organic matter with a maximum of 50%, while nitrate contributed more to aerosol extinction only in Southern California, exceeding 30%. The difference in extinction between the east and west was more significant than the difference in aerosol concentration because of the higher relative humidity in the east than in the west. In China, sulfate and organic matter were the main components of extinction, accounting for 21%–57% and 21%–39%, respectively, and nitrate was the main extinction component only in central China, exceeding 30%. The reconstructed extinction coefficient had both low values of overestimation and high values of underestimation (-60%–35%). The more severe the pollution, the more obvious the underestimation. Aerosol concentration and extinction level are significantly higher in China than in the United States. IMPROVE equation has obvious uncertainties to underestimate high extinction coefficient and to overestimate low extinction coefficient in China. The uncertainty will have a negative impact on the accurate implementation of air pollution prevention and blue sky program. It is urgent and significant to carry out the accurate accounting extinction of aerosol components and tracing the aerosol sources, which will provide scientific program to control the aerosol sources for improving atmospheric visibility in the various environmental climate regions.

• Thermodynamic characteristics of winter onset in Northern Asia

  Fu Shiyi, Shi Ning

  Available online:December 20, 2023  DOI: 10.3878/j.issn.1006-9895.2308.23075

  Abstract(172) HTML(0) PDF(3.08 M)( 1212)

  Abstract:Based on the daily reanalysis data of the Japan Meteorological Agency (JRA55) from 1958 to 2020, the thermal budget characteristics before and after winter onset in North Asia (50°-75°N,80°-140°E) and the external forcing factors that affect winter onset are studied. The result shows that the climatological winter onset in North Asia occurs in the sixty-second pentad. Before the onset, North Asia experienced a process from drastic cooling to slow down. In this process, the diabatic cooling plays a major role, which is partially offset by the warm advection. Based on the linear baroclinic model, the diabatic cooling in the middle and high latitudes of the Eurasian continent is conducive to the formation of westerly and southerly winds in North Asia, resulting in strong local warm advection, and then partially counteracting the cooling effect of the diabatic heating itself. On the interannual time scale, the sea surface temperature anomalies in the Equatorial east-central Pacific and North Atlantic both affect winter onset in North Asia through anomalous wave train on the Eurasian continent, and they show significant signals one month and five months in advance, respectively, which has certain predictive significance. In terms of its impact on winter temperatures, the temperature in some parts of East Asia and southern China is higher (lower) in December in the early (late) year of winter onset in North Asia.

• Effect of Physical Parameterization Scheme Combined with Perturbation on Ensemble Prediction Quality

  WEI LIQING, MIN JINZHONG, YANG TING

  Available online:December 20, 2023  DOI: 10.3878/j.issn.1006-9895.2306.22219

  Abstract(107) HTML(0) PDF(8.82 M)( 1049)

  Abstract:There are many parameters in the cloud microphysics scheme and the constraint relationship between the parameters is complex, so it has not been decided what parameters should be selected and how to carry out the parameter combination disturbance in the ensemble forecast. Based on WRFv4.2 model, this paper selects eight parameters of WSM6 scheme to conduct the ensemble prediction experiment of parameter disturbance for the heavy rainfall event of Meiyu front in 2020. Contrast and analyze the influence of different parameters and different disturbance range combinations on prediction, and try to jointly disturb the sensitive parameters of cloud microphysical scheme and boundary layer scheme. The results show that the combined disturbance of the 4 sensitive parameters of the cloud microphysics schemes has the best performance in the prediction test, which reduces the False Alarm Rate of torrential rain probability forecast, and improves the spread skills of humidity field, zonal wind, temperature field in low level and meridional wind in middle troposphere. The combined disturbance of the raindrop truncation parameter and the maximum of the cloud ice diameter presents a synergistic resonance effect, which can effectively improve the ensemble prediction effect. However, combined perturbations between graupel truncation parameters, graupel density and truncation parameters show that disturbance energy does not increase with the increase of disturbance parameters, and the antagonism between parameters will restrict the improvement of ensemble forecasting skills. The disturbance of three parameters in the MRF boundary layer scheme has significantly improved the ensemble prediction skill of low layer humidity field, and the combined disturbance of three parameters is better than that of a single disturbance; At the same time, joint perturbation of the cloud microphysical parameter perturbation scheme and boundary layer parameter perturbation scheme can achieve the best effect. It shows that the selection of parameter and the range of the disturbance can affect the effect of the ensemble forecast, a collaborative relationship between the parameters of the combination is easy to obtain a better forecast effect, while parameter combinations with antagonistic effect show negative skills. Multi parameter disturbance considering the dependency relationship between parameters and the range of disturbance is more conducive to the improvement of ensemble prediction effect, which provides a valuable reference for the selection of parameters in parameter disturbance in the future.

• Macroscopic and microscopic physical characteristics of two supercooled fog processes in Lushan Mountain

  WANG Tianshu, NIU Shengjie, WANG Ying, ZHAO Junjie, LIANG Mian, WANG Yuan, FAN Dongliang, YANG Feiyun, WANG Tao, ZHANG Hongwei, Yuan Wei

  Available online:December 20, 2023  DOI: 10.3878/j.issn.1006-9895.2309.23070

  Abstract(200) HTML(0) PDF(2.50 M)( 1009)

  Abstract:Comprehensive fog observation campaigns at Lushan Meteorological Bureau of Jiangxi Province were conducted with a fog drop spectrometer and an automatic weather station in January and December of 2016, respectively. This study investigated the physical characteristics (macro and micro) of supercooled fog and elucidated its evolution mechanism. Combining observational data with NCEP 1°×1° reanalysis data, the macro and micro physical characteristics of two supercooled fogs cases (case 1 on January 16-17, 2016, while case 2 on December 25-27, 2016) were analyzed. Our results revealed that the evolutions of the two supercooled fogs were strongly correlated with the movement of cold front. From the formation stages to the development stages, the dominated wind direction below 800 hPa changed from southwest to northerly, the front edge of the cold front arrived at the study area, and the temperature near the surface decreased sharply in both cases. At the mature stages of the two supercooled fogs, the rain stopped at the near-surface and the wind force weakened, meanwhile, the front inversion layer appeared in case 2. During the dissipation stages, the wind direction in 900-500 hPa changed into north in both cases and the wind speed below 800 hPa increased obviously. For micro characteristics, the average droplet spectra exhibited bimodal distributions in both cases, with the main peaks at 4.9 μm. However, the secondary peaks were at 8.9 and 11.0 μm in case 1 and case 2, respectively. Both cases presented instantaneous droplet spectra with the main peaks between 10 to14 μm, and the frequency were 12.4% and 46.3% in case 1 and case 2, respectively. Both cases had a transition from warm fog to supercooled fog. Compared with the warm fog, the number density of supercooled fog droplets in each size increased, especially for droplets with particle size below 14 μm. The correlation between fog droplet number concentration and average diameter in the whole process of case 1 was weak, which may be affected by factors such as fog droplet collision-coalescence and droplet competition for water vapor. Case 2 showed positively correlation among the fog droplet number concentration, average diameter and water content in the whole process, which indicated that the fog process was dominated by condensation nuclei activation and condensation growth. The strong low-level jet in southwest, the obviously decreased temperature in near-surface, and the inversion layer were all found in case 2, resulting in the wider droplet spectrum, the more prominent peak between 10 and 14 μm particle sizes in droplet spectrum, moreover, higher values of number concentration, average diameter, and water content comparing with case 1.

• Characteristics of Large scale circulation anomaly configuration and its evolution for extreme heavy precipitation events in the west of Sichuan Basin based on classified weather pattern

  Longguang Chen, Chen, Chen, Xiangde Xu

  Available online:December 18, 2023  DOI: 10.3878/j.issn.1006-9895.2303.23017

  Abstract(171) HTML(0) PDF(2.91 M)( 1134)

  Abstract:The western side of the Sichuan Basin is one of the regions with the highest frequency of extreme heavy precipitation events (HPEs) in China. However, due to the complexity of terrain and atmospheric circulations systems, the formation mechanism of HPEs remains elusive. Based on the gauged data by China Meteorological Administration from 2001 to 2020, GPM-IMERG precipitation and ERA5 reanalysis data, we selected 100 extreme HPEs in the west of Sichuan Basin, and classified these HPEs into three categories with K-means clustering method. Then, the anomalies of atmospheric circulation and its evolution with respect to different category of HPEs are explored. The results show that, during the period of precipitation, the geopotential height is characterized by a positive anomaly at the upper-level (200hPa) and negative anomaly at the lower-level (850hPa), together with the enhanced vertical wind speed, a "top-cold and bottom-warm" atmospheric temperature structure, and the increased water vapor transport departing from the low latitude ocean area. However, their atmospheric circulations configuration, including the South Asian High, the Western Pacific Subtropical High, and the westerly jet in upper level, shows obvious difference and plays a dominant role in in shaping the precipitation formation of different types and associated water vapor transport: For category 1 HPEs ranked the highest frequency of occurrence, its associated water vapor transport mainly comes from the Bay of Bengal and the South China Sea, which controlled both by the Indian monsoon and the East Asian monsoon. As to category 1, HPEs occurs with the strengthened WPSH, and its water vapor mainly comes from the South China Sea, while the water vapor transport from the Bay of Bengal is restricted. When it comes to the category 3, its water vapor transport mainly controlled by the East Asian monsoon. Prior to the occurrence of HPEs, it can be found that the Rossby wave action shows an increasing trend, the atmospheric vertical wind speed increase significantly, and the temperature anomaly was more significant. These features are conducive to the occurrence of extreme precipitation events. The results also indicates that the changes in WPSH position and intensity on synoptic time scales are better indicators for the prediction of heavy precipitation formation compared to SAH.

• Exploration of the development and evolution mechanism of the Southwest Vortex from a new vortex development indexLu Ping1, 2

  Institute of Plateau Meteorology

  Available online:December 18, 2023  DOI: 10.3878/j.issn.1006-9895.2311.23092

  Abstract(347) HTML(0) PDF(1.19 M)( 1307)

  Abstract:Based on the ERA5 (0.25° × 0.25°) hourly reanalysis data, this paper analyzes two different high-impact Southwest Vortex (SWV) processes with long-distance movement and stagnation over local area. It is suggested that two physical variables, the low- to mid-level convergence and pseudo-equivalent potential temperature, are the key factors influencing the development and evolution of the vortex. According to these findings, a vortex development index is defined in this study. By comparing the vortex development index with the evolution of the SWV and precipitation, we found that: (1) the vortex development index could indicate the development and evolution trend of the intensity and position of the vortex, whether it is a long-distance moving or a local stationary SWV process. The index could also reveal the occurrence of other weak closed lows or multi-core vortices during intense vortex events, as well as the moving mechanism of the SWV. (2) The vortex development index not only indicates the intensity and coverage area of vortex precipitation but also reflects the coexistence phenomenon between the SWV and precipitation, thereby providing a possible explanation for both the "rain-induced vortex" and the "vortex-induced rain" phenomenon. Results of this study suggest the positive significance of the vortex development index in the forecast of both the precipitation distribution and the position of the precipitation center of the high-impact SWV heavy rainfall events.

• Potential vorticity source, potential vorticity circulationand their weather and climatic significance

  Wu Guoxiong, SHENG Chen

  Available online:December 07, 2023  DOI: 10.3878/j.issn.1006-9895.2306.23319

  Abstract(150) HTML(0) PDF(3.90 M)( 1141)

  Abstract:Based on a brief review of the research progress of surface potential vorticity, this paper introduces the calculation of potential vorticity and its generation under complex terrain, and the research progress on the source of potential vorticity and potential vorticity circulation in recent years, focusing on the particularity of the surface potential vorticity on the Tibetan Plateau and its important influence on weather and climate. It is clarified that for adiabatic and frictionless atmospheric motion, the structural recombination of the potential vorticity itself (potential vortex reconstruction) can cause the development of vertical vorticity, which can excite the formation of plateau vortex in summer and make the eastern part of the plateau an important source of surface vorticity in winter. Based on the derived equation for the vertical motion associated with isentropic displacement () and including diabatic heating, it is further demonstrated that the eastward propagation of the positive vorticity created on the Tibetan Plateau along the westerly wind will cause the development in the downstream area of cyclonic vorticity, southerly wind, and upward motion in the lower troposphere, resulting in the increase of potential vorticity advection with altitude, which stimulates the development of extreme weather and climate events. It was pointed out that the diurnal variations of surface heating and latent heat release at the cloud bottom over the Tibetan Plateau significantly affect the diurnal variation of the potential vorticity near the surface, resulting in the development of the low-vortex and precipitation system over the Tibetan Plateau from late afternoon to night. It is proved that compared with the traditional surface sensible heating index, the surface potential vorticity index of the Tibetan Plateau can better characterize the seasonal changes of local precipitation, and is more closely related to the Asian summer monsoon precipitation. The concept of potential vortex circulation (PVC) is also briefly introduced. It is pointed out that since the change of convergence of PVC across the close boundary of an area is directly related to the change of potential vorticity of the area, in order to maintain the relative stability of the total potential vorticity in the northern hemisphere, the change of PVC on the trans-equatorial plane and the change of surface PVC must complement each other, so the change of the potential vortex circulation on the trans-equatorial plane can be considered a window for monitoring near-surface climate change. The near-equatorial air-sea interaction can directly cause the change of vertical shear of the zonal wind on the vertical plane across the equator, stimulate the trans-equatorial PVC anomaly, and thus affect the climate change near the surface of the northern hemisphere through the change of PVC in the atmosphere and the regulation of the Tibetan Plateau. The analysis shows that PVC analysis opens up a new way for establishing the link between tropical and extra-tropical atmospheric circulation changes, and has broad application prospects.

• The progress on vortices in China in the past ten years

  Sun Jianhua

  Available online:December 07, 2023  DOI: 10.3878/j.issn.1006-9895.2311.23323

  Abstract(248) HTML(0) PDF(4.14 M)( 1269)

  Abstract:In recent years, the disastrous weather, such as heavy rainfall and severe convection occur frequently in China, and vortices is one of the important weather systems that produce these disastrous weathers. In order to improve the understanding and prediction accuracy of the mechanism of vortices, and their producing heavy rainfall and severe convective weathers in China, this paper mainly summarizes the important research results of three types of vortices (Tibetan Plateau vortex, Southwest vortex and Dabie vortex) along the Yangtze River basin, Northeast cold vortex and Central Asian vortex in northern China in recent ten years. This paper mainly reviews the identification methods, statistical characteristics of spatial and temporal distribution, three-dimensional structure of these vortices, as well as the formation mechanism of heavy rainfall and severe convection weathers associated with the vortices in the past ten years. Finally, a brief discussion and outlook are given on the future directions in research and forecasting related to vortex systems and their weathers.

• Analysis of evolution characteristics, physical mechanism and impacts of marine heatwaves in the Western Pacific Warm Pool under the background of triple-year La Nina from 2020 to 2022

  Zheng Fei, Zhang Xiaojuan, Cao Tingwei

  Available online:December 07, 2023  DOI: 10.3878/j.issn.1006-9895.2311.23325

  Abstract(352) HTML(0) PDF(2.17 M)( 1119)

  Abstract:Under the influence of global warming, the continuously growing Marine Heatwaves (MHW) has a serious impact on the climate system and the social economy, of which the Western Pacific Warm Pool area is a typical area of MHW characteristic changes. Based on the MHW database, the National Centers for Environmental Prediction (NCEP) atmospheric and oceanic reanalysis data, the chlorophyll-a concentration data provided by the National Aeronautics and Space Administration (NASA) Aqua satellite and the biogeochemical Argo floats, by using statistical methods such as composite analysis and singular value decomposition (SVD), we explore the evolution characteristics, physical mechanisms and ecological impacts of MHW in the Western Pacific Warm Pool from 2020 to 2022. The results show that MHW properties in the Western Pacific Warm Pool region have increased significantly in the past 30 years and it is closely related to the continuous La Ni?a events. Under the background of multi-year La Ni?a events from 2020 to 2022, the frequency of MHW in the Western Pacific Warm Pool reached the highest in the world, and the coverage area, frequency, total days and cumulative intensity of MHW are the most notable since 1982. By using the mixed layer heat budget equation in the Western Pacific Warm Pool region, it is shown that the occurrence of the strongest MHW during the period 2020 to 2022 is mainly dominated by the downward shortwave radiation term in the net flux and the latitudinal advection term in the marine dynamic processes. In addition, we also revealed that the MHW properties and marine ecological indicator chlorophyll-a concentration show a negative correlation on the spatial and temporal scales in the Western Pacific Warm Pool region, especially the MHW events during 2020-2022 caused the significant decline of overall phytoplankton biomass in the upper ocean of the region.

• The patterns of carbon and water exchange process over different types of ecosystems in the southeastern margin of the Tibetan Plateau

  Huizhi Liu, Qun Du, Lujun Xu, Yang Liu, Xiaoni Meng, Yamei Shao, Yingqi Zheng

  Available online:November 29, 2023  DOI: 10.3878/j.issn.1006-9895.2309.23315

  Abstract(210) HTML(0) PDF(2.40 M)( 1037)

  Abstract:The Hengduan Mountains situated in the southeast margin of the Tibetan Plateau is in the conjunction area of the south Asia monsoon and southeast Asia monsoon, and it is also the heating area and sensitive area of the atmospheric change. It is of great importance for the understanding of the key processes of the atmospheric water resource in the Tibetan Plateau to investigate the effects and its parameterization schemes of the interaction between the land surface and the atmosphere on the water and energy exchange processes in this region. It is introduced about the land-atmospheric filed experiments developed in this area based on the continuous eddy covariance measurements. It is also analyzed about the patterns of the exchange process between the wetland/ lake/ grassland surfaces and the atmosphere in Erhai lake, Lijiang alpine grassland and Tengchong Beihai wetland land surface process observation sites. In addition, the characteristics of local circulation simulated with numerical models are also investigated in complex mountainous areas. The characteristics of land-atmosphere surface exchange process and their influencing factors for different types in the southeastern edge of the Tibetan Plateau and Hengduan Mountains have been preliminarily identified and revealed. The main conclusions are as follows: the carbon and water exchange processes in alpine meadows in the southeastern edge of the Tibetan Plateau are significantly influenced by precipitation distribution. In addition to meteorological factors, the carbon and water exchange in "floating blanket" wetlands with grass floating on the surface like blanket for whole year is also affected by changes in underlying surface vegetation and water proportion. The influencing factors of carbon and water exchange processes in different types of ecosystems vary at different time scales. Wind speed is always a key factor influencing latent heat and CO2 exchange in lakes, while precipitation also has a significant impact on CO2 flux in lakes at longer time scales. Furthermore, the complex terrain in the southeastern edge of the Tibetan Plateau has a significant impact on the ecosystem carbon and water exchange processes. Different types of local circulations generated by complex terrain have different effects on the carbon and water exchange processes of ecosystems

• A Comparative Study on the Contributions of Interdecadal SST Variability over the Pacific and North Atlantic Ocean to Regional and Seasonal Trends of Antarctic Sea Ice from 1979 to 2014

  Yang Luping, Wu Qigang, Hu Yuantao, Hu Aixue

  Available online:November 28, 2023  DOI: 10.3878/j.issn.1006-9895.2310.23100

  Abstract(151) HTML(0) PDF(4.76 M)( 1078)

  Abstract:Based on the latest satellite-derived sea ice concentration (SIC) data, this study investigates the seasonal and spatial characteristics of Antarctic sea ice trends from 1979 to 2014, and examines the relative contributions of the Interdecadal Pacific Oscillation (IPO) and Atlantic Multidecadal Oscillation (AMO) phase shift to the Antarctic sea ice trend and associated mechanisms. Results indicate that SIC in the Ross Sea and the Indian Ocean showed increasing trends in the four seasons, and the annual and seasonal Antarctic sea ice extent (SIE) exhibited significant increase trends from 1979 to 2014. During the warm seasons (December-May), SIC decreased significantly in the Amundsen-Bellingshausen Seas and decreased in the Weddell Sea ice, resembling a positive phase of Antarctic Dipole (ADP). During the cold seasons (June-November), the SIC trends in Amundsen-Bellingshausen-Weddell Seas showed a negative phase of ADP. The shift of IPO from a positive to negative phase during 1979-2014 deepened the Amundsen Sea Low (ASL) by exciting Pacific-South America (PSA) atmospheric teleconnection and significantly contributed to the negative phase of ADP in the austral winter and spring. During the austral spring, the shift of AMO from a negative to positive phase during 1979-2014 enhanced the ASL through the excitation of the Rossby wave and PSA wave train across the South Pacific basin and weakened the Ekman suction that would advert less warm water upward, contributing to the negative ADP and increased sea ice trend in the eastern Ross Sea, Amundsen Sea and Indian Ocean and explaining about 75% of the austral spring Antarctic SIE increased trend. In the austral summer, the above IPO and AMO phase transitions might have enhanced the Southern Annular Mode (SAM) and thus contributed to the increased trend of Antarctic sea ice. Our results suggest the seasonality and regionality of impacts of the IPO and AMO phase shifts on Antarctic sea ice trends through the atmospheric teleconnection mechanisms.

• Multi-scale effects of Tibetan Plateau-Indian Ocean thermal contrast on South Asian monsoon activity

  Xiao Ziniu, Li Zhangqun

  Available online:November 24, 2023  DOI: 10.3878/j.issn.1006-9895.2310.23324

  Abstract(361) HTML(0) PDF(2.87 M)( 1147)

  Abstract:The land-sea thermal contrast is the fundamental driving force for the Asian summer monsoon formation and evolution. Tibetan Plateau-Indian Ocean thermal contrast is a crucial factor influencing South Asian monsoon activity. This article reviews and summarizes the relevant research results about the impacts of the Tibetan Plateau-Indian Ocean thermal contrast on South Asian monsoon activity at different time scales, including sub-seasonal, seasonal, inter-annual, and inter-decadal scales. On the sub-seasonal scale, the main focus is on the influence of the thermal contrast on the onset of the South Asian monsoon. On the inter-annual scale, the emphasis is on the indicative significance of the thermal contrast for the interannual variation of monsoon intensity. On the inter-decadal scale, the inter-decadal variations in the relationship between the thermal contrast and South Asian monsoon precipitation are examined. Meanwhile, the article discusses some issues that need further research in this field.

• Waveguide teleconnections in boreal summer: Progress and perspective

  王林, Xu Peiqiang

  Available online:November 24, 2023  DOI: 10.3878/j.issn.1006-9895.2311.23322

  Abstract(180) HTML(0) PDF(2.78 M)( 1337)

  Abstract:Waveguide teleconnections are quasi-stationary planetary waves propagating along the jet stream waveguide. They play an essential role in the maintenance and evolution of atmospheric circulation, and their abnormal activities are often associated with extreme weather and climate events. Studying the variation and mechanism of waveguide teleconnections at different timescales can not only deepen our understanding of the dynamics of atmospheric circulation but also serve as a scientific basis for weather forecasting, climate prediction, and even climate projection at corresponding timescales. According to the dynamical property of the jet stream waveguide, the atmospheric waveguide can be divided into the subtropical jet waveguide, which is maintained essentially by the barotropic effect, and the polar front jet waveguide, which is primarily maintained by the baroclinic effect. This paper focuses on the waveguide teleconnections in the boreal summer over the Eurasian region, when and where waveguide teleconnections are the most active. It first reviews the history and theory of waveguide teleconnection and then summarizes some recent advances in waveguide teleconnections along the subtropical jet and polar front jet, including their formation conditions, dynamic mechanisms, climate impacts, and future changes. Finally, it discusses some possible issues that deserve future investigation.

• Understanding the influence of background mean-state field on ENSO tropical and extratropical teleconnection from an energetic perspective

  Huang Gang

  Available online:November 20, 2023  DOI: 10.3878/j.issn.1006-9895.2305.23304

  Abstract(141) HTML(0) PDF(2.00 M)( 1054)

  Abstract:El Ni?o-Southern Oscillation (ENSO) influences global weather and climate through teleconnection patterns. In tropical regions, ENSO can induce precipitation and sea surface temperature anomalies over remote ocean basins by influencing tropical tropospheric temperatures. In extratropical regions, ENSO can pose climate impacts over regions such as North America and Asia through the excitation of quasi-stationary Rossby waves. The background mean-state fields are of vital importance to ENSO"s tropical and extratropical teleconnections. On one hand, the background mean-state atmospheric circulations can influence the position and intensity of ENSO teleconnection wave trains through barotropic and baroclinic energy conversion. On the other hand, the tropical background mean-state sea surface temperature and convection fields can influence ENSO"s tropical teleconnection processes through the adjustment of moist static energy distribution. These studies suggest that analyzing energetic processes can help to understand the mechanisms through which the background mean-state fields influence ENSO teleconnections. The present study reviews the progress in energetic analysis researches on the impacts of the background mean-state fields on ENSO"s tropical and extratropical teleconnections in recent decades. Based on it, this study will further review the potential changes of ENSO teleconnections under global warming, and propose some important scientific questions that need to be studied in the future.

• Recent Progresses in the study on Arctic-midlatitude connection and its association with Arctic sea ice loss

  Wu Bingyi

  Available online:November 20, 2023  DOI: 10.3878/j.issn.1006-9895.2309.23305

  Abstract(190) HTML(0) PDF(4.96 M)( 1511)

  Abstract:This paper provides an overview of recent (2018-2023) progresses in the research filed of the Arctic-Eurasian midlatitude linkage and its association with Arctic sea ice loss. The progress includes the following aspects: (1) There is a substantial understanding of the contribution of Arctic sea ice melting in an extreme snowfall event in Europe, which cannot be explained by the mechanism that Arctic sea ice variations affect atmospheric circulation proposed in previous studies. (2) The response of winter Asian regional temperatures to the continuous melting of Arctic sea ice exhibits significant low-frequency oscillation characteristics. The continuous melting of Arctic sea ice is conducive to the alternating occurrence of warm Arctic-cold Eurasia (2004/05-2012/13) and warm Arctic-warm Eurasia (2013/14-2016/17). In the war Arctic-cold Eurasia phase, the enhanced Arctic-midlatitude connection was observed, while in the warm Arctic-warm Eurasian phase, the linkage between the Arctic and East Asia weakened. However, the mechanism by which sea ice melting affects the strength of the Arctic-Eurasian connection is unclear. (3) At summer mean and sub-seasonal time scales, summer heatwaves in the mid- and low-latitudes of East Asia are dynamically linked to the simultaneous cold anomalies in the mid- and low-troposphere over the Arctic. Arctic summer cold anomalies are conducive to not only slowing down Arctic sea ice melting, but also provide a precursor signal for predicting East Asian winter monsoon. (4) Arctic sea ice loss does not produce substantial impact on summer precipitation variability in the region south to North China. (5) Although there are many studies stressing the important roles of the troposphere-stratosphere interactions in linking Arctic sea ice loss to weather events and climate variability in the midlatitudes, the causal-effect linkage is still weak, and the uncertainty of the impact of the stratosphere process on weather events and climate variability is greater than that of the troposphere process. (6) It is no longer practical to distinguish the different roles of Arctic sea ice forcing and atmospheric internal variability in weather events and climate variability. In the future, more attention should be paid to the role of Arctic sea ice melting in resulting low-frequency atmospheric circulation variability, as well as the impacts of the spatial distribution differences in Arctic sea ice anomalies and different abnormal amplitudes. Additionally, quantitative research is also needed to explore the roles of Arctic sea ice melting in extreme weather and climate events.

• Hybrid downscaling models for real-time predictions of summer precipitation in China on monthly–seasonal scale

  fanke, tianbaoqiang, daihaixia

  Available online:November 20, 2023  DOI: 10.3878/j.issn.1006-9895.2308.23312

  Abstract(119) HTML(0) PDF(7.83 M)( 1311)

  Abstract:Large inter-month variations of summer precipitation tend to cause alternations or transitions of extreme drought and flood in China, but seasonal averages may cover alternations on monthly scale, and affect the prediction skills on seasonal scale. Thus, it is necessary to improve the forecast of monthly climate which contribute to the enhancement of predictions on seasonal scale. This study focuses on the real-time predictions of monthly precipitation at 160 stations in China during the summer season (June, July, and August) with the year-to-year increment method and the field information coupled pattern method, and further calculate the seasonal precipitation with monthly predictions. The information from preceding observations and simultaneous predictions from the second version of Climate Forecast System (CFSv2) are considered. Consequently, the observed sea surface temperature (SST) over the mid-high latitude of the South Pacific in December, the observed sea ice concentration (SIC) in the critical region of the Arctic in January, and the simultaneous SST from CFSv2 released in February are selected as predictors to develop the downscaling model. Prediction models based on individual predictors are established firstly to evaluate the prediction skills of different predictors, and then the singular value decomposition (SVD) error correction method is applied to diminish the errors of downscaling models. The optimized ensemble scheme is also adopted to synthesize hybrid downscaling models for summer precipitation over China on monthly scale with higher stability, and further seasonal prediction is conducted with results on monthly scale. The re-forecast results during the period 1983?2022 showed that the hybrid downscaling models derived from the optimized ensemble scheme exhibit comprehensive prediction skills compared with single-predictor models. The percentages of stations, at which the time anomaly correlation coefficients of re-forecast results are larger than the 90% confidence level, count for 90%, 88%, and 82% respectively for June, July, and August. The mean values of the spatial anomaly correlation coefficients are respectively 0.39, 0.40, and 0.39, passing the 99% confidence level. For real-time prediction, the hybrid downscaling models perform well at both monthly and seasonal scales during 2020?2022, when summer precipitation situations are anomalous and different from each other under similar La Ni?a events. The averaged Ps scores of real-time predictions are respectively 75, 75, and 70 for precipitation in June, July, and August. The Ps scores for summer precipitation derived from monthly predictions are 72, 76, and 73 from 2020 to 2022, which are higher than the multi-year-averaged Ps score of real-time forecasts. Hence, seasonal predictions derived from effective monthly forecasts would improve the prediction skills of climate predictions on monthly–seasonal scale.

• Review of High Resolution Climate System Model Development and Application

  俞永强, An bo, Liu Hai Long, Bao Qing, Lin Peng Fei, He Bian, Zheng Wei Peng, Luan Yi Hua, Bai Cong Rong

  Available online:November 20, 2023  DOI: 10.3878/j.issn.1006-9895.2308.23317

  Abstract(198) HTML(0) PDF(20.62 M)( 1190)

  Abstract:One of the major trends in the development of climate system models today is to improve the ability to simulate multi-scale interaction processes and extreme events in the climate system by increasing the spatial resolution of climate models. In the past five years, scientists from the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS) have developed and improved the 25 km resolution atmospheric circulation model FAMIL2.2 and the 1/10 degree resolution ocean circulation model LICOM3.0, and established the high resolution climate system model FGOALS-f3-H based on them. A large number of numerical simulations and climate predictions have been carried out using the above high-resolution models, including the high-resolution model comparison project (HighResMIP) of the sixth phase of the international Coupled Model Inter-comparison Project (CMIP6), and the establishment of an ocean circulation prediction system (LFS). Preliminary diagnosis and analyses show that compared to low-resolution models, high-resolution models can better simulate important weather and climate events such as typhoons, extreme precipitation, oceanic mesoscale eddies, and mesoscale sea-air interaction processes.

• Interpretation of physicochemical processes of typical ozone pollution in a suburb of Beijing

  Jia Long, Yu Shanshan, Xu Yongfu

  Available online:November 17, 2023  DOI: 10.3878/j.issn.1006-9895.2311.23309

  Abstract(266) HTML(0) PDF(4.17 M)( 1459)

  Abstract:Ozone pollution is a significant environmental problem for some cities in China at present. The ozone formation depends on the chemical reactions affected by the atmospheric physical process and various meteorological conditions, so it is necessary to study near-ground ozone pollution from both chemical and physical aspects. This study analyzed the physicochemical processes of photochemical pollution in Huairou, an urban city in Beijing, in autumn 2022, by combining field observations and the Eulerian photochemical box model simulations. The daily variation characteristics of meteorological factors, such as temperature, relative humidity, and wind speed, and the concentrations of ozone and its precursors, volatile organic compounds (VOCs) and nitrogen oxides (NOx, x=1, 2), are determined. The results of source analysis show that the primary sources of VOCs were traffic emissions (46%), plant sources (25%), solvent evaporation (23%) and combustion process (9%). The contribution of ozone from regional transport and reactions of local VOCs was obtained based on the Euler photochemical box model. The results show that ozone was mainly from horizontal transport (> 74%) during the strong north wind prevailing period. During weak south or southeast winds, O3 was formed primarily by VOCs and NOx photochemical reactions. According to the ozone formation potential of VOCs, alkenes contribute the most to ozone formation, accounting for 67%, followed by aromatics (16%). Sensitivity analysis shows that ozone formation is most sensitive to physical factors, such as light intensity, temperature and boundary layer height; meanwhile, reactive alkenes are the most sensitive among VOCs. Finally, O3 pollution control strategies are suggested based on the EKMA curves.

• Quantitative study of atmospheric oxidation capacity

  王跃思, 刘子锐

  Available online:November 17, 2023  DOI: 10.3878/j.issn.1006-9895.2311.23318

  Abstract(246) HTML(0) PDF(2.61 M)( 1532)

  Abstract:Atmospheric Oxidation Capacity

• An Introduction to Tropical Waves

  Liang Wu, Tao Feng, Ronghui Huang

  Available online:November 08, 2023  DOI: 10.3878/j.issn.1006-9895.2310.23321

  Abstract(252) HTML(0) PDF(2.66 M)( 1516)

  Abstract:This paper provides an overview of the theoretical solutions for shallow water equations and the characteristics of tropical waves. It also presents systematic methods for identifying equatorial waves from observations. Recent advancements in tropical wave observational studies have revealed several mechanisms that affect tropical wave evolutions, such as wave-flow interaction, wave-cumulus convection interaction, and moisture mode. Local large-scale circulation and cumulus convection play a critical role in controlling the structure, intensity, and movements of tropical waves. This paper also reviews the impact and mechanism of tropical waves on the formations and tracks of tropical cyclones. By examining tropical waves, the multiscale variation of tropical cyclone activity can be explained well. However, further research is necessary to address scientific problems related to atmospheric tropical waves to advance tropical atmospheric dynamics.

• In Memory of Our Mentor—Academician Ye Duzheng—Overview of His Academic Achievements and Serious and Careful Spirit of Scholarship

  Huang Ronghui, Huang Gang

  Available online:November 08, 2023  DOI: 10.3878/j.issn.1006-9895.2310.23302

  Abstract(484) HTML(0) PDF(1020.59 K)( 1110)

  Abstract:This paper is written to commemorate the 10th anniversary of our mentor-academician Ye Duzheng’s pass away and his great contributions to the development of atmospheric sciences in China and Institute of Atmospheric Physics, Chinese Academy of Sciences. This paper aims to make a brief review of his main contributions to the atmospheric sciences. Over more than 70-year research career, he proposed the theory of energy dispersion of Rossby wave, which has been one of classical theories of Dynamic Meteorology. Moreover, he established the theory of atmospheric general circulation over East Asia and the Tibetan Plateau Meteorology. Especially, he proposed a scale theory regarding the adaptation process of atmospheric motion and the new concept of adaptation to global warming. Besides, this paper provides an overview of his outstanding contribution to the development of Institute of Atmospheric Physics, Chinese Academy of Sciences and his serious and careful spirit of scholarship.

• Progress on the evolutionary characteristics and climatic causes of warming and marine heatwaves in the coastal China seas

  蔡榕硕

  Available online:November 08, 2023  DOI: 10.3878/j.issn.1006-9895.2310.23313

  Abstract(536) HTML(0) PDF(2.60 M)( 1627)

  Abstract:Robust warming and frequent extremely high sea temperature events (marine heatwaves, MHWs) have been observed in the coastal China seas (CCS) over the past decades, causing a series of ecological disaster, including mass mortality of marine organisms and outbreaks of harmful algal blooms. This paper presents a comprehensive review of the research progress involving the warming and marine heatwaves in the CCS, including the characteristics and causes of long-term warming trend and MHWs, as well as their ecological impacts and adaptation strategies. Under the combined influences of the East Asian monsoon and Kuroshio, the sea surface temperature (SST) in the CCS, especially in the East China Sea (Bohai, Yellow and East China Seas), has shown an enhanced response to global warming, with annual mean increases of 1.02 ±0.19°C and 1.45±0.32°C during the period of 1960-2022, respectively, with significant inter-decadal and inter-annual variability. In addition to the influence of large-scale air sea interaction such as ENSO and PDO, SST changes are also directly affected and jointly affected by the East Asian Monsoon changes and the Kuroshio meridional transport. The ocean warming has caused rapid northward migration of geographic isotherms and seasonal phenological changes (spring arrives earlier and fall begins later than normal), resulting in the changes in the growth rhythm, geographic distribution, community structure and ecological service functions of marine organisms. Frequent extreme MHWs have caused devastating disasters to some marine ecosystems such as coral reefs and aquaculture. In the future, the mid-high latitudes of CCS will be simultaneously exposed to the enhanced warming, deoxygenation, acidification, and reduced productivity; and sever climate tipping points of marine ecosystems such coral reef ecosystems in the South China Sea are very likely to triggered in the near future. There is an urgent need for in-depth research on the physical processes and predictability of marine heatwaves, as well as the forecasting and early warning systems. Furthermore, transformative climate action measures should be developed to enhance the climate resilience of ocean systems, and strong mitigation measures need to be taken as soon as possible to slowdown global warming.

• Progress in the Study of Impacts of the tropical air-sea interactions on the East Asian Summer monsoonCHEN Wen_{1, 2}^{, YU Tiantian}₂^{, FENG Juan}₂^{, CHEN Shangfeng}₂^, PIAO jinling^₂

  Chen Wen

  Available online:November 08, 2023  DOI: 10.3878/j.issn.1006-9895.2310.23310

  Abstract(168) HTML(0) PDF(2.37 M)( 1348)

  Abstract:Among the factors that influencing the East Asian summer monsoon (EASM), tropical sea surface temperature (SST) is the main reason for the variation of the East Asian summer monsoon system. In recent decades, the studies on the influences of the tropical SST anomalies on the EASM have achieved great progress. From sub-seasonal, interannual to interdecadal timescales, this paper has briefly reviewed the advances in the studies on impacts of the tropical air-sea interactions on the EASM and the associated mechanisms, with focuses on the main progress of the impacts of El Ni?o–Southern Oscillation (ENSO), tropical Indian Ocean and Atlantic. In addition, roles of tropical SSTs in the link between EASM and the East Asian Winter monsoon are also systematically reviewed. Finally, we put forward several related issues that need to be further investigated in the future, for instance, the impact of tropical SST anomalies on the sub-seasonal variation of EASM, tropical SST changes under global warming and its impact on the EASM.

• Seasonal variation and temporal-spatial scale dependence of air-sea relationship

  WU, SUN Xiaoshan

  Available online:November 08, 2023  DOI: 10.3878/j.issn.1006-9895.2310.23303

  Abstract(155) HTML(0) PDF(1.13 M)( 1374)

  Abstract:This study reviews the seasonality and temporal-spatial scale dependence of the air-sea relationship based on recent analyses of the relationship between surface turbulent heat flux and sea surface temperature. The contents include the representation, regional change, seasonal change and temporal and spatial scale variation of surface turbulent heat flux-sea surface temperature relationship as well as relative contributions of surface wind speed and sea-air humidity difference to changes in surface latent heat flux-sea surface temperature relationship. The surface turbulent heat flux-sea surface temperature relationship displays notable differences between the mid-latitude oceanic frontal zones and subtropical gyre regions. In the mid-latitude oceanic frontal zones, the oceanic process has a main contribution to sea surface temperature variations, indicative of an oceanic forcing, which is stronger in winter than in summer. In the subtropical gyre regions, surface turbulent heat flux plays a major role in sea surface temperature variations, indicative of an atmospheric forcing, which is more obvious in summer than in winter. In the western Arabian Sea, the oceanic process has an obvious influence on sea surface temperature variations in summer, indicative of an oceanic forcing, whereas the surface turbulent heat flux has a major influence in winter, indicative of an atmospheric forcing. In the Bay of Bengal, the South China Sea and the Philippine Sea, the atmospheric forcing is prominent in both winter and summer. In the mid-latitude ocean frontal zones during winter and the western Arabian Sea during summer, the oceanic forcing increases with the time scale, whereas in the other regions and seasons, there exists a transition from the atmospheric forcing in shorter time scales to the oceanic forcing in longer time scales with the transition time scale of about 20-40 days. In the mid-latitude oceanic frontal zones, the oceanic forcing decreases with the increase of the spatial scale and switches to the atmospheric forcing with the transition spatial scale shorter in summer than in winter. The atmospheric forcing usually enhances with the increase of the spatial scale.

• Research on extreme climate in middle and high latitudes of Asia -- Brief introduction to the content and progress of major projects funded by the National Natural Science Foundation

  Wang Huijun

  Available online:November 08, 2023  DOI: 10.3878/j.issn.1006-9895.2310.23301

  Abstract(150) HTML(0) PDF(605.02 K)( 1010)

  Abstract:In recent years, the frequency and intensity of extreme climate keep increasing significantly, particularly in China (Yin et al., 2023b), which poses more and more threats to the social-economic and life security. Chinese scientists are also paying more and more attention to the extreme climate in China and East Asia. In contrast, although the middle and high latitudes of Asia are also highly sensitive to climate change, they have received relatively little attention, which may be due to the relative lack of climatic data, or may be related to the low population and economic and social development in the high latitudes of Asia (especially Siberia). In fact, with the deepening of the research on the amplification effect of the Arctic warming, it is extremely necessary to carry out the research on the impact of climate change and extreme climate in the middle and high latitudes of Asia, and extend our research concern from East Asia to the north. There are many key scientific issues to be investigated, especially the processes, mechanisms and predictability of climate extremes in the region, their impact on ecosystems, and their future evolution. Therefore, the Geoscience Division of the National Natural Science Foundation of China supported this research as a major project on a merit-based selection (the project implementation period is 2020-2024). In this paper, the author briefly introduced the framework of the project and some preliminary research progresses.

• Typical case study of Impact of a typical Eastward-Propagating Mesoscale Convective System over the Second-Step terrain on its downstream rainfall

  Yang Ruyi, Zhang Yuanchun, Sun Jianhua, Mu Jianli, Yu Tingzhao

  Available online:November 08, 2023  DOI: 10.3878/j.issn.1006-9895.2309.23080

  Abstract(237) HTML(0) PDF(6.03 M)( 1239)

  Abstract:A typical mesoscale convective system (MCS) over the second-step terrain that moved eastward, merged with convection moving eastward from the eastern edge of the Tibetan Plateau (TP), and influenced the downstream convection systems, had been studied using a numerical simulation. The case occurred from June 29 to July 1, 2016, and resulted in heavy precipitation in the middle reaches of the Yangtze River to the Yangtze-Huai River Basin. This simulation had successfully reproduced the eastward movement of the MCSs over the second-step terrain and the merging with convection moving eastward from the TP, which affected the downstream convective systems. The results revealed the spatiotemporal distribution of precipitation over the middle and lower Yangtze River. The evolution of the MCS is divided into four stages: the formation stage, the propagation stage, the merging stage, and the weakening stage. Due to the cyclonic disturbance in the northeastern part of the Southwest Vortex, the MCS formed in the western mountainous area over the second-step terrain. After moving eastward out of the second-step terrain, the MCS merged with the eastward-propagating convection from the eastern edge of the TP over the downstream areas, which promoted the strong development of upward motion, enhanced the convergence in the lower layers, and induced a mesoscale vortex in the lower troposphere. The mesoscale vortex and the merged convection gradually coupled, triggering heavy rainfall in the eastern plains east of the second-step terrain.

• Long-term ground based remote sensing of aerosol optical properties in Beijing

  Chen Hongbin, Shi Hongrong, Fan Xuehua, Xia Xiang''ao

  Available online:October 26, 2023  DOI: 10.3878/j.issn.1006-9895.2309.23320

  Abstract(147) HTML(0) PDF(2.01 M)( 1731)

  Abstract:Long-term observations of aerosol optical properties are critical for quantifying aerosol radiative forcing and climate effects, as well as for studying air quality and environmental health. This paper provides a systematic review of the global AERONET network and introduces the development and research achievements of the AEROENT Beijing station, which has the longest observation time in China. Based on more than twenty years of observation data from the Beijing station, the multi-time scale variability of optical radiation products is analyzed. The importance and urgency of long-term observations are also discussed.

• Research progress on the influence of interdecadal transition of interannual variability of spring snow over the Tibetan Plateau on East Asian summer monsoon

  zhangchao, Duan Anmin

  Available online:October 26, 2023  DOI: 10.3878/j.issn.1006-9895.2309.23306

  Abstract(208) HTML(0) PDF(1.98 M)( 1483)

  Abstract:Tibetan Plateau (TP) snow anomalies (TPSA) in winter-spring is one of the important predictors of the East Asian summer monsoon (EASM). This paper systematically reviews the studies on the impacts of the interdecadal transition of TPSA on the EASM in recent 20 years. The main conclusions are as follows: (1) interannual variability of the TPSA shows a striking shift from an east-west dipole to a mono-sign structure, which was affected by the sea surface temperature anomalies in the North Pacific and tropical Atlantic, and also bound up with the Antarctic Oscillation and Arctic Oscillation. (2) The interdecadal change of the TPSA in spring influences the EASM precipitation by impacting the subtropical westerly jet in the upper troposphere and the low-level moisture transport. (3) The TPSA can impact the Meiyu rain belt through the “TP atmospheric river” mechanism. (4) The Atlantic Muti-decadal Oscillation can modulate the relationship between the spring TPSA and the Meiyu precipitation. This relationship is robust (weak) during the positive (negative) phase of the Atlantic Muti-decadal Oscillation. Finally, this paper discusses the and prospects the key scientific issues in the influence of the TPSA on the EASM.

• Review on Development and Application of CNMM-DNDC -- A Three-Dimension, High-Resolution and Process-Oriented Terrestrial Hydro-Biogeochemical Model

  Zheng Xunhua, Li Yong

  Available online:October 26, 2023  DOI: 10.3878/j.issn.1006-9895.2305.23314

  Abstract(259) HTML(0) PDF(4.46 M)( 1356)

  Abstract:The CNMM-DNDC, which is developed by the authors, is a three-dimension (3D), high-resolution and process-oriented terrestrial hydro-biogeochemical model that fully couples the cycling processes of carbon (C), nitrogen (N), phosphorous (P) and water in terrestrial ecosystems at site, catchment, regional, or global scales. Here, this model is reviewed in terms of development background, basic ideals and theories, core scientific processes, characteristics and features, comprehensive functions, verification by observations, and preliminary applications at site, regional or catchment/basin scales. Since the publication of its first version in 2018, this model has undergone several scientific process improvements and function enhancements. As a result, the cycles of C, N, P elements and water have been fully coupled in this model through numerically linking a series of biogeochemical reactions of these life elements, and matter phase changes and mechanical movements, which are occurring in terrestrial earth surface systems. Wide validations with field comprehensive observations demonstrate that the CNMM-DNDC model can be generally applicable for long time 3D and “3H” integrative simulations of terrestrial ecosystems in different bioclimatic zones from tropical to boreal permafrost regions, wherein the “3H” is referred to high spatial, high temporal and high process resolutions. As this model is designed to well describe the biogeochemical transformations and the 3D movements of the three life elements and water at different (site, ecosystem, catchment/basin, regional or global) scales, available validations and preliminary applications so far have demonstrated its potential to simultaneously predict multiple variables to measure the sustainability in terms of the United Nations Sustainable Goals (SDGs). The predictable variables include at least hydraulic soil erosion, surface runoff and subsurface flow, leaching of water and C, N and P solutes, horizontal flows of dissolved and particle C, N and P substrates or matter, emissions of greenhouse gases (carbon dioxide, methane, and nitrous oxide) and gaseous N pollutants (ammonia and nitric oxide), ecosystem productivity, water evapotranspiration, and balances of energy, water, C, N and P. The CNMM-DNDC model is expected to provide advanced technical support of numerical simulation for the multiple-goal implementations of the SDGs, as it could be a) a robust tool for virtually experimental studies on complex processes at different scales and b) a core model of a decision supporting system to optimize carbon and environmental management.

• Evaluation of CMIP6 models in simulating the sensitivity of LAI to temperature and precipitation change over China

  Danyun Wang, Xiaodong Zeng, Xiang Song

  Available online:October 20, 2023  DOI: 10.3878/j.issn.1006-9895.2304.22067

  Abstract(272) HTML(0) PDF(3.05 M)( 1721)

  Abstract:Evaluation of climate and vegetation status in earth system models (ESMs) is fundamental to understanding climate change, terrestrial ecosystems, and the carbon cycle. In this study, the temperature, precipitation, and LAI in the growing season over China from eighteen ESMs of the Sixth International Coupled Model Comparison Project (CMIP6) were evaluated based on site observation and remote sensing data. Then, a multiple linear regression model was used to quantify the sensitivity of LAI to temperature and precipitation, and to evaluate the ability of the CMIP6 model to simulate the sensitivity of vegetation in geographical and climatic spaces. At last, the models with a better simulation performance were selected. The results show that (1) Most models can simulate the spatial distribution of temperature, precipitation, and LAI in the growing season, but there are obvious deviations in their mean value and change trends. (2) Compared with the observation, The simulation ability of LAI sensitivity to temperature and precipitation showed that the simulation of the positive region was better than the negative region, and the sensitivity of vegetation in ecotone was greater than that in China. There was a large deviation in the amplitude of vegetation sensitivity and its distribution in climate space (i.e., the corresponding relationship with climate field). (3) Comprehensively based on evaluations above, CANESM5-CanOE, INM-CM5-0, IPSL-CM6-LR, and MPI-ESM1-2-LR have the best performance on simulations of climate and vegetation during the growing season in China.

• Mosaicking hybrid-tilt radar reflectivities from S- or C-band weather radars and X-band phased array radars

  Zhu Ziwei, Qi Youcun

  Available online:October 10, 2023  DOI: 10.3878/j.issn.1006-9895.2306.23055

  Abstract(595) HTML(0) PDF(1.10 M)( 1383)

  Abstract:The changing climate has increased the frequency of hazardous weather events, which has placed higher demands on monitoring hazardous weather. In addition to the conventional S-band and C-band operational radar networks, in recent years, many cities in China have built X-band weather radar monitoring networks to improve the spatiotemporal resolution of hazardous weather monitoring and the low-level observation information of weather systems. Hybrid-tilt reflectivity is extracted from the multi-tilt radar measurements over the radar domain, which is closest to the surface and not affected by orographic blockage. It is important for monitoring the occurrence and development of convective systems. In order to take advantages of the wide detection range of S-band or C-band weather radars and the high spatiotemporal resolution of X-band weather radars, this study presents a method of mosaicking hybrid-tilt radar reflectivities derived from the measurements of S-band or C-band and X-band weather radars. This method includes 1) generation of hybrid-tilt reflectivity, 2) conversion of radar reflectivity in different frequencies, and 3) mosaicking of reflectivity measurements from multiple radars. Based on this method, the hybrid-tilt reflectivity mosaic products of Shenzhen and Xi’an are generated, with the spatial resolution of 30 m and the temporal resolution of 1 min. During the events of different precipitation types, the hybrid-tilt reflectivity mosaic products are evaluated using the reflectivity measurements from the Dual-frequency Precipitation Radar onboard the Global Precipitation Measurement Core Observatory (GPM-DPR). The result shows that the hybrid-tilt reflectivity mosaic products are highly consistent with the GPM-DPR reflectivity measurements, and the mean errors are within ±1dB.

• Impacts of Atlantic Multidecadal Oscillation (AMO) on the East Asian Climate: A Review

  JIANG Dabang, 司东

  Available online:October 10, 2023  DOI: 10.3878/j.issn.1006-9895.2307.23311

  Abstract(380) HTML(0) PDF(1.39 M)( 2114)

  Abstract:We have reviewed recent researches associated with the Atlantic Multidecadal Oscillation (AMO) and its influences on East Asian climate. Specifically, we focus on the drivers, index definitions, impacts on East Asian summer and winter climates of the AMO as well as the combined effects of the AMO and other Oceans. Until now, the mechanisms of the AMO are still under debate. The AMO is considered to be caused by the multidecadal Atlantic Meridional Overturning Circulation (AMOC) variability, the external forcings (e.g., aerosols) or the stochastic atmospheric forcing. The positive phase of the AMO can strengthen the East Asian summer monsoon and increase the summer precipitation and temperature over East Asia through three ways, and vice versa. Meanwhile, under the positive AMO phase, the East Asian winter monsoon system is strong and the mid-latitude Eurasian continent and northern China are cold, and vice versa. Given the importance of AMO, further understanding the drivers of AMO and its climatic impacts on East Asian climate is conducive to improving decadal to interdecadal predictions of East Asian climate.

• Comparative study on the influence of different NWP model background on the 100-meter integrated temperature and wind forecasts in complex terrain

  Song Linye, Yang Lu, Cheng Conglan, Chen Mingxuan, Cao Weihua, Wu Jiankun

  Available online:October 07, 2023  DOI: 10.3878/j.issn.1006-9895.2306.23059

  Abstract(203) HTML(0) PDF(4.18 M)( 1204)

  Abstract:Based on the high resolution integrated forecast system of RISE, using the meso-scale CMA-BJ model with 3km resolution and the global-scale ECMWF model with 0.125 degree resolution, adopting the hourly observation data of conventional and dense automatic weather stations, taking the outdoor mountainous competition area in Beijing Winter Olympics as the research area, this study compares the effects of different numerical weather prediction (NWP) model background on the accuracy of surface 2-m temperature and 10-m wind analysis and hourly forecast for the future 1-24h with 100m grid resolution. The results show that: (1) Both the regional and global models can be used as the background of RISE system to effectively form 100-meter fine integrated products in complex terrain, but the impacts of different NWP model backgrounds on the analysis and forecast performance for different meteorological elements are obviously different; (2) For temperature analysis, the model background has the least influence. The spatial distribution of RISE temperature analysis with CAM-BJ and ECMWF as the NWP model background is basically the same, and the MAE error is both less than 0.2oC; (3) For wind analysis, adopting high-resolution regional model can improve the refinement level of RISE high-precision wind integrated products better than the global model with coarse resolution; (4) For temperature forecast, the performance of RISE 100m grid forecasts with ECMWF model background is significantly better than that with CMA-BJ model background, and the average forecast errors for Winter Olympic alpine stations and all stations are reduced by 10.5% and 7.0%, respectively. (5) For wind speed forecast, the MAE errors of 1-6h forecast for RISE Winter Olympics alpine stations with CAM-BJ and ECMWF model backgrounds are 1.42m/s and 1.30m/s, respectively, and the MAE errors of 7-24h forecast are 1.52m/s and 1.54m/s, respectively. Besides, the average 1-24h MAE errors for all stations in RISE region are 1.38m/s and 1.24m/s, respectively. The results in this study are helpful to further understand the role of model background in the 100-meter-level integrated forecast, and have important scientific significance and practical value for improving the accuracy of weather forecast in complex terrain.

• The Influence of Turbulent Diffusion Driven by Fog-Top Radiative Cooling on Heavy Fog in North China Plain

  Meng TIAN, Bingui WU, Yunchen LIAO, Jianbo YANG, Hailing LIU

  Available online:September 15, 2023  DOI: 10.3878/j.issn.1006-9895.2307.22249

  Abstract(169) HTML(0) PDF(3.25 M)( 1229)

  Abstract:Radiative cooling at the top of fog is a crucial physical process during the evolution of fog, driving a “top-down” turbulent mixing. Therefore, the YSU (Yonsei University) scheme incorporates a module (ysu_topdown_pblmix) to represent this process. However, the influence of such “top-down” turbulent mixing on heavy fog events in the North China Plain remains unclear. This study evaluates the suitability of ysu_topdown_pblmix in simulating fog events in the North China Plain based on Himawari-8 satellite retrievals, automatic station observations, 15-layer atmospheric boundary layer gradient measurements, and 5-layer turbulence-related observations. Large-eddy simulations are also used to supplement the analysis. The investigation reveals that while ysu_topdown_pblmix overall decreases the fog area simulation scores in the North China Plain, it significantly improves the simulation of near-surface temperature, humidity, and fog boundary layer structure. This enhancement is attributed to the “top-down” turbulent mixing driven by radiative cooling at the fog top. However, the present ysu_topdown_pblmix exhibits an excessive entrainment effect, leading to too much intrusion of warm air above the fog top, resulting in rapid dissipation of fog. Sensitivity tests demonstrate that reducing the evaporative enhancement coefficient in ysu_topdown_pblmix can mitigate the strength of turbulent entrainment at the fog top, thereby improving the simulation of fog events. These findings suggest that incorporating ysu_topdown_pblmix is necessary for numerical simulations of heavy fog events in the North China Plain, but further refinement of relevant parameters is required.

• Analysis of vertical characteristics of a transitional snow event based on weather radars in Fujian

  Guan Xiaojun, Qi Youcun

  Available online:August 31, 2023  DOI: 10.3878/j.issn.1006-9895.2306.23063

  Abstract(274) HTML(0) PDF(4.99 M)( 1471)

  Abstract:A transitional snow event occurred in Fujian Province on 19 to 23 February 2022 and was characterized by the co-existence of warm layer in the middle troposphere and cold layer in the lower troposphere. Multiple precipitation types occurred on the ground including rain, snow and wet snow, etc., increasing the difficulty of forecasting. Based on data from weather radars and other sources, , a classification method of precipitation types is firstly used to identify the time periods of snow and wet snow at each weather station, on this basis, the influence of environmental temperature evolution on transitional snow event as well as the vertical characteristics of transitional snow event are investigated by analyzing synoptic circulation and vertical features of radar variables. The results show: (1) the transition between snow and wet snow could be clearly distinguished according to the characteristics of VPR and environmental temperature information in areas that topography and surface temperature are uniformly distributed, that is, VPR monotonously increases with decreasing height during snow stage, while a significant bright band presents in the middle layer of VPR during wet snow stage. Great emphasis should be put on the capability of weather radars in observing precipitation in the lower level. If radar variables could not capture the change of precipitation characteristics caused by the difference of temperature in the near-surface layer due to the limitation of observation environment, the precipitation types on the ground could be markedly different even though the VPR features resemble each other in higher layer. (2) the vertical characteristics of polarimetric radar variables indicate that, the growth mechanism of hydrometeors in the upper layer and above melting layer is similar to general dry snow events, the major differences of transitional snow events are the complicated melting and refreezing processes of particles caused by the warm layer and cold layer. A bright band signature displays when hydrometeors falling through warm layer, then melted particles are fully or partially frozen reaching the ground as snow or wet snow, depending on the intensity of cold layer beneath warm layer and temperature at surface. The vertical features of radar variables (e.g. the change of intensity of bright band) could timely reflect the change of environmental temperature, which is conductive to distinguish precipitation types and could make up for the inaccurate forecasting of numerical model and the absence of atmospheric profiles to some extent.

• Anthropogenic radiative forcing accelerated snow ablation in the eastern Tibetan Plateau in recent winter and spring

  Liao Shujie, Wu Qigang, Sun leng, Yao yonghong, Hu yuantao

  Available online:August 31, 2023  DOI: 10.3878/j.issn.1006-9895.2306.23051

  Abstract(185) HTML(0) PDF(5.85 M)( 1134)

  Abstract:The winter and spring snow depths on the eastern Tibetan Plateau (TP) are characterized by interdecadal variability, with a significantly increased trend approximately before 1990 and a decreased trend after 1990. In this paper, we first analyze trends of winter and spring snow depth over the eastern TP in 1960-1989 and 1990-2014, and its relationships with the trends of temperature, precipitation and other atmospheric circulation conditions. Three sets of outputs from the CESM2 model, including (1) total external radiative forcing, (2) well-mixed greenhouse gas radiative forcing, and (3) anthropogenic aerosol radiative forcing, are then used to assess the respective contributions of radiative forcing and North Atlantic Oscillation (NAO) to the trends of snow depth in the eastern TP during the winter-spring period of 1960-1989 and 1990-2014. Observational analyses indicate that the post-1990 snow reduction was mainly caused by increasing surface air temperature and decreasing snowfall, while spring snow depth was mainly caused by increasing surface air temperature. During 1960-1989, all radiative forcing, greenhouse-gas forcing only, or aerosol forcing only contributed little to increased trends of winter and spring snow depth over the eastern TP. The NAO instead contributed about 49% of increased trends of winter snow depth over the eastern TP, but little of increased trends of spring snow depth over the eastern TP. Comparison of observed and modelled trends in other atmospheric variables suggests that all radiative forcing led to significant warming and reduced snowfall on the eastern TP from 1990-2014, and contributed significantly to the continued reduction in both winter and spring snow depths in the later period, explaining 29% and 82% of the observed winter snow depth reduction in the later period. Both greenhouse gas forcing and aerosol radiative forcing contribute significantly to plateau warming and together contribute to the reduction in snow depth in the eastern TP in winter and spring during 1990-2014. The decreasing trend in the NAO index can explain 22% of the reduction in snow depth in the eastern TP in winter from 1990-2014, but contributes slightly to the reduction in snow depth in spring. With future increases in anthropogenic greenhouse gases and decreases in aerosol emissions, warming in the eastern TP is expected to intensify further and snow depth in this area will continue to decrease.

• Extreme Precipitation in the South China Sea and Surrounding Areas: Observation and Projection

  Yang Song, Xu Lianlian

  Available online:August 29, 2023  DOI: 10.3878/j.issn.1006-9895.2307.23308

  Abstract(129) HTML(0) PDF(4.11 M)( 1058)

  Abstract:The South China Sea and surrounding areas (SCSSA) is one of the most sensitive regions with strong sea-land-air interactions. Extreme precipitation over the region has received widespread attentions in recent decades, because its large latent heat can exert substantial impacts on climate variability across the globe, through providing substantial energy and moisture for global atmospheric circulations. Utilizing gauge-based gridded data and a statistically downscaled CMIP6 dataset, we systematically investigate the historical and future spatiotemporal characteristics of maximum 1-day precipitation (RX1day), maximum 5-day precipitation (RX5day), very heavy precipitation days (R20) and very wet days (R95p) over this region. The RX1day, RX5day, R20, and R95p are commonly used to represent heavy rainfall, persistent heavy rainfall, high-frequency heavy rainfall, and accumulated heavy rainfall amount, respectively. Result shows that four indices share an analogous spatial pattern during 1951-2014 at annual and seasonal time scales, with large values appearing over Southeast Asia, the Southern China, and southern part of the Tibetan Plateau. That is, these regions are not only with heavy rainfall, but also manifest sustained and high-frequency heavy precipitation. The four indices show large values over Southeast Asia in four seasons, and depict great (small) values over South Asia, the Tibet Plateau, and East Asia in summer (winter). The projected four indices in the future maintain the historical spatial structures, and the four indices averaged over the whole region exhibit increasing trends during 2015-2100 under the SSP1-2.6 and the SSP5-8.5 scenarios. The percentage changes in the four indices during 2016-2035, 2046-2065, and 2080-2099 under two scenarios with respective to 1995-2014 exhibit slightly decrease in Southeast Asia and East Asia, and increase over South Asia and the Tibetan Plateau. In addition, the physical mechanism associated with extreme precipitation over Southeast Asia has been further explored. The cold sea surface temperature anomalies (SSTAs) over Indian Ocean, warm SSTAs over the tropical North Atlantic, and SSTAs over the tropical Pacific and Atlantic are responsible for southern dry and northern wet, overall wet, and northern dry and southern patterns of extreme precipitation over Southeast Asia, respectively.

• Simulation of regional meteorological elements and rainstorms in China by two resolution Global Forecast System

  JIA Jia, DAN Li, WANG Lizhi, Zhan Siyu, Ma Zhuguo

  Available online:August 09, 2023  DOI: 10.3878/j.issn.1006-9895.2305.23067

  Abstract(197) HTML(0) PDF(2.69 M)( 1589)

  Abstract:The improvement of numerical weather prediction depends on the improvement of the model physical process, the model initial field and model spatial resolution. The improvement of the model resolution has become an effective way to improve the model prediction effect. Based on the global forecast system, T1534 (13km) and T254 (55km) models with different resolutions were used to forecast the temperature, pressure, wind speed and precipitation over China. The results show that, among the two resolution models, North China has the best forecast effect. The correlation coefficients with ERA5 reanalysis data are all above 0.8, and the root-mean-square errors of the seven subregions decrease significantly with the increase of resolution. In the simulation of air temperature, the root-mean-square error in southwest China is 2.171, which is reduced by 30.1% to 1.523 after the model resolution is improved. In the simulation of wind speed, the correlation coefficients of the two resolution products are generally higher in the monsoon region than in the non-monsoon region. In a region with complex terrain, such as northwest China, the root-mean-square error of wind speed increases slightly with the increase of model resolution. It can be seen that the improvement of model resolution may not necessarily improve the accuracy of wind speed forecast. According to the heavy precipitation weather process in Shandong on August 10, 2019, the two models with different resolutions can simulate the precipitation characteristics well and cover the actual precipitation falling area. The deviation scores of various precipitation grades predicted by the high resolution model are lower than those of the low resolution model. In this heavy precipitation process, the relative humidity was close to saturation on the precipitation day, which was easy to condense, and with the improvement of the model resolution, the relative humidity was enhanced and the structure became more refined. Meanwhile, the central pressure of the low-level cyclone simulated by the high resolution model was lower than that of the low-resolution model, and the cyclone intensity was greater and the convective precipitation process was stronger.

• Atmospheric Electricity Research in China: A Review

  QIE Xiushu, ZHU Jiangwan, DI Shaoxuan, LUO Shuoming, HUANG Zifan, LIU Dongxia, ZHANG Hongbo, YUAN Shanfeng, LIU Mingyuan, SUN Zhuling, XU Chen, SUN Chunfa, WANG Dongfang, JIANG Rubin, YANG Jing

  Available online:August 09, 2023  DOI: 10.3878/j.issn.1006-9895.2306.23307

  Abstract(307) HTML(0) PDF(2.23 M)( 2337)

  Abstract:Atmospheric electricity mainly studies the electrical processes occurring in the Earth"s atmosphere and near-Earth space as well as their mechanisms and effects. The core research contents are lightning physics and thunderstorm electricity. Since the 1980s, Atmospheric electrical research has continuously made new progress in China. Thanks to the advances in high-time-resolution lightning detection technology, the research on atmospheric electricity has not only achieved important results in the aspects of lightning physics and thunderstorm cloud charge structure, but also in the impact of lightning and thunderstorms on the near-Earth space, and the characteristics of lightning in strong convective weather, and lightning data assimilation and early warning and forecasting of lightning have made important progress. This paper summarizes recent research progress of atmospheric electricity in China in the past five years from six aspects, including high-precision lightning detection technology, lightning physical process and mechanism, the impact of thunderstorms on the middle and upper atmosphere, observation and numerical simulation of thundercloud charge structure, characteristics and forecast of lightning in strong convective weather, the impact and response of lightning on climate change, etc. Based on this review, key priorities for future research on the atmospheric electricity are highlighted.

• Characteristics of Cold Vortexes in Northeast Asia and their Impact on Precipitation Distribution of Warm Seasons over Northeast China

  HUANG Lijun, CUI Xiaopeng, CHEN Liqiang

  Available online:July 13, 2023  DOI: 10.3878/j.issn.1006-9895.2304.23030

  Abstract(311) HTML(0) PDF(2.63 M)( 1518)

  Abstract:In this study, 3730 cold vortexes (CVs) in Northeast Asia from 2000 to 2019 are objectively identified and tracked, including "short duration" CVs that last [6, 24) and [24, 48) hours and traditional northeast CVs that last at least 48 hours. Differences in the spatial and temporal distribution, intensity, and scale characteristics of CVs of different durations, and their impact on precipitation over Northeast China during warm seasons, are further investigated. The results show that: (1) CVs with a duration of [6, 24) hours are the most common, accounting for about 60%, while traditional CVs are the least, about 15%. (2) CVs are more likely to occur from May to August, but CVs with different durations peak in different months. (3) The high occurrences of CV centers with durations of [6, 24), [24, 48), and ≥48 hours appear in the northeast corner, northeast quadrant, and central part of the identification region, respectively. The first moments of CV centers mainly occur near the western boundary between 45°–55°N, and CV centers with a duration of [6, 24) and [24, 48) hours are also more frequent in the northeast quadrant and north-central part, respectively. The last moments of CV centers are located near the eastern boundary of the identification region north of 40°N. (4) The longer the CVs last, the stronger the CV centers and the larger the CV sizes. The CVs are stronger and larger in cold seasons than in warm seasons. (5) The average ratios of total precipitation and short-time heavy precipitation under CVs are both more than 60% (the latter is larger). The longer the duration of CVs, the larger the ratios. The spatial distributions of total precipitation and short-time heavy precipitation under different durations of CVs present remarkable differences. The research on “short duration” CVs also needs more attention.

• 东北冷涡低温影响的关键环流型及其机理研究

  CHEN chen, XIE Zuowei

  Available online:May 06, 2023  DOI: 10.3878/j.issn.1006-9895.2304.23015

  Abstract(460) HTML(0) PDF(5.80 M)( 1599)

  Abstract:Northeast China cold vortex (NCCV) often induces low temperature and cold damage in Northeast China during summer, resulting in "Dumb Disaster" to the "Northeast Granary". Using the fifth-generation reanalysis data of ECMWF, this paper analyzes the key circulation configuration, as well as formation and maintenance mechanism of NCCV with low temperature impact during early summer (May–June) over 1979–2021. The results show that two ridges over Lake Baikal and the Okhotsk Sea as well as NCCV form a typical inverted "Ω" circulation, which favors invasions of cold air and high potential vorticity from the high latitude region into Northeast China. At the same time, easterlies on the south flank of high over the Okhotsk Sea bring cold air into Northeast China. These two cold air intrusions together cause the abnormally cold in Northeast China. The "- + -" Rossby wave train from the eastern European Plain to Lake Baikal is the precursor of NCCV, which is incipiently amplified by the diabatic heating and friction. Subsequently, the Rossby wave plays a major role, which causes the high potential vorticity intruding southward and accumulating. The East Asian jet barotropically deforms such high potential vorticity to form a deep NCCV. As the downward dispersion of Rossby wave energy and the dissipation of diabatic heating and friction, NCCV weakens drastically. When the quasi-stationary ridge maintains over the north of Lake Baikal, it cuts off the connection between Northeast China and the cold air and high potential vorticity over the high latitude region. The Rossby wave hardly leads NCCV to develop and thus NCCV has no obvious low temperature impact over Northeast China.

• Simulating land and atmosphere exchange processes over a mountainous forest in Huainan using CLM4.5

  DAI Qiudan, Guo Zhenhai, Wang Longhuan, Sun Xiangming, Xie Zhenghui, Sun Shufen, and Xiao xia

  Available online:May 06, 2023  DOI: 10.3878/j.issn.1006-9895.2304.22186

  Abstract(272) HTML(0) PDF(2.08 M)( 1562)

  Abstract:Using the ERA5 single-layer reanalysis data combined with the planetary boundary layer tower (PBL tower) meteorological observations from a north-south climate transition zone mountainous forest in Huainan as forcing data, we evaluate the applicability of the Community Land Model (CLM4.5) against observed canopy flux and micrometeorological data at this site. Also three experiments to study the impact of soil texture on soil moisture are designed to improve the model performance. The results show that overall CLM4.5 performances good in Huainan mountainous forest, and the simulated results driven by observation is better than that of ERA5 data. In terms of radiation simulation, both the simulated results of the radiation components using ERA5 data and PBL tower observation data are good, especially driven by PBL tower observation, and the correlation coefficient between the simulation results and observations throughout the year is more than 0.97, and the root mean square error is below 25.056 W m-2. The correlation coefficient of the ERA5 forcing simulation is slightly lower, but it also reaches 0.92, and the root mean square error is below 29.939 W m-2; In terms of soil temperature, both the correlation coefficients reach more than 0.98; the correlation coefficients of soil moisture results are all above 0.86, but systematically higher; and the average correlation coefficients of the simulated results of the sensible heat flux are 0.72 and 0.78, respectively. Through the comparison simulating tests of three soil texture parameters, it is shown that the simulated results of the soil moisture with the measured three layers of soil texture plus the data of the deep soil texture are closest to the observation. Thus the accurate description of the soil texture can greatly improve the simulation of soil moisture. But further tuning of the parameters or parameterization scheme is still needed. In addition, the ERA5 reanalysis single-layer data as forcing in this site are reliable, and thus can be used in the further simulating work. This study could be useful for further study of land and atmosphere exchange in the north-south climate transition zone of Huainan, China.

• Comparative study on the high-resolution vertical distribution characteristics of meteorological elements and atmospheric pollutants in the boundary layer of sunny day and radiation fog events based on UAV observation

  WU Haopeng, NIU Shengjie, LIU Duanyang, LÜ Jingjing, ZU Fan, ZHOU Yue, WANG Yuan, GE Panyan, WANG Lingling, LU Haining

  Available online:December 23, 2022  DOI: 10.3878/j.issn.1006-9895.2210.22180

  Abstract(306) HTML(0) PDF(3.08 M)( 1226)

  Abstract:In order to further study the vertical distribution characteristics of meteorological elements and pollutant concentrations in the boundary layer of radiation fog events, a comprehensive observation test of boundary layer and pollutants was carried out in Donghai County by UAV in the winter of 2020. It is found that the thickness of inversion layer in foggy days is tens to hundreds of meters thicker than that in sunny days, and the strength is stronger by 0.5-1℃/hm. On foggy days, there is wind shear at low altitude, and the wind direction changes little in the vertical direction. On sunny day, the wind speed changes little at low altitude, and the wind direction rotates clockwise with height at low altitude. The intensity of radiation fog with deep single-layer inversion structure is stronger than that of double-layer inversion structure. In the same radiation fog process, the intensity of fog will not change with the change of wind direction, and the lower wind speed is more conducive to the formation of strong fog. From the perspective of vertical distribution of pollutants, TVOC at the same height in the inversion layer is higher in sunny days than in foggy days. Before and during the generation stage of radiation fog, the decrease rate of SO₂ concentration with height is much higher than that in the same period of sunny days. In sunny and foggy days, the vertical changes of O₃ and NO₂ show obvious negative correlation, and NO₂ shows a negative gradient change. PM_1.0, PM_2.5 and PM₁₀ are more than twice higher in foggy days than in sunny days. CO is relatively stable in the process of radiation fog with little vertical change. TVOC, NO₂, PM_1.0, PM_2.5 and PM₁₀ will be affected by the strong inversion in the process of radiation fog and accumulate in the inversion layer. The cumulative change rate of particulate matter is more significant than that of gas, and the cumulative change rate of particles with large particle size decreases more than that of particles with small particle size. The decrease of PM_2.5 concentration will reduce aerosol optical thickness and promote photochemical activity photolysis reaction, resulting in a negative correlation between PM_2.5 and O₃ vertical change. After sunrise, the solar radiation is enhanced, and the development of unstable boundary layer is accompanied by the downward mixing of O₃ in the upper air, which leads to the increase of O₃ and the increase of PM_2.5 emission, making the vertical changes of the two more consistent.

• The definition and detection of the abrupt climatic change

  Fu Conghin, Wang Qiang

  1992,16(4):482-493, DOI: 10.3878/j.issn.1006-9895.1992.04.11

  Abstract (13693) HTML (0) PDF (0.00 Byte) (9197)

  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.

• Analyses of the Causes of Severe Drought Occurring in Southwest China from the Fall of 2009 to the Spring of 2010

  HUANG Ronghui, LIU Yong, WANG Lin, WANG Lei

  2012,36(3):443-457, DOI: 10.3878/j.issn.1006-9895.2011.11101

  Abstract (11387) HTML (0) PDF (7.74 M) (7468)

  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.

• Assessing the Quality of APHRODITE High-Resolution Daily Precipitation Dataset over Contiguous China

  HAN Zhenyu, ZHOU Tianjun

  2012,36(2):361-373, DOI: 10.3878/j.issn.1006-9895.2011.11043

  Abstract (10869) HTML (0) PDF (12.25 M) (7372)

  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.

• Influence of heat source anomaly over the western tropical Pacific on the subtropical high over East Asia and its physical mechanism

  Huang Ronghui, Li Weijing

  1988,12(s1):107-116, DOI: 10.3878/j.issn.1006-9895.1988.t1.08

  Abstract (10863) HTML (0) PDF (0.00 Byte) (419)

  Abstract:

• Interdecadal Variation of the Leading Modes of Summertime Precipitation Anomalies over Eastern China and Its Association with Water Vapor Transport over East Asia

  HUANG Ronghui, CHEN Jilong, LIU Yong

  2011,35(4):589-606, DOI: 10.3878/j.issn.1006-9895.2011.04.01

  Abstract (10289) HTML (0) PDF (6.09 M) (8406)

  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.

• An Overview of Recent Studies on Atmospheric Boundary Layer Physics and Atmospheric Environment in LAPC

  ZHANG Meigen, HU Fei, ZOU Han, et al

  2008,32(4):923-934, DOI: 10.3878/j.issn.1006-9895.2008.04.18

  Abstract (10003) HTML (0) PDF (1.90 M) (21569)

  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。

• Recent Progress of Atmospheric Boundary Layer Physics and Atmospheric Environment Research in IAP

  Hu Fei, Hong Zhongxiang, Lei Xiaoen

  2003,27(4):712-728, DOI: 10.3878/j.issn.1006-9895.2003.04.18

  Abstract (9704) HTML (0) PDF (736.82 K) (11832)

  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.

• Advances in Studies of Pacific Decadal Oscillation

  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 (9488) HTML (0) PDF (1.32 M) (12756)

  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.

• Projection and Evaluation of the Precipitation Extremes Indices over China Based on Seven IPCC AR4 Coupled Climate Models

  JIANG Zhihong, CHEN Weilin, SONG Jie, et al

  2009,33(1):109-120, DOI: 10.3878/j.issn.1006-9895.2009.01.10

  Abstract (9224) HTML (0) PDF (806.32 K) (7594)

  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.

• Analyses on the Spatial Distribution of Aerosol Optical Depth over China in Recent 30 Years

  Luo Yunfeng, Lu Daren, Zhou Xiuji, Li Weiliang

  2002,26(6):721-730, DOI: 10.3878/j.issn.1006-9895.2002.06.01

  Abstract (9086) HTML (0) PDF (0.00 Byte) (7192)

  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.

• Characteristics of the Water Vapor Transport in East Asian Monsoon Region and Its Difference from that in South Asian Monsoon Region in Summer

  Huang Ronghui, Zhang Zhenzhou, Huang Gang, Ren Baohua

  1998,22(4):460-469, DOI: 10.3878/j.issn.1006-9895.1998.04.08

  Abstract (8904) HTML (0) PDF (0.00 Byte) (7155)

  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。

• A Study on the Relationships between ENSO Cycle and Rainfalls during Summer and Winter in Eastern China

  Jin Zuhui, Tao Shiyan

  1999,23(6):663-672, DOI: 10.3878/j.issn.1006-9895.1999.06.03

  Abstract (8737) HTML (0) PDF (413.03 K) (7413)

  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。

• The Impact of Variation of Sea-Ice Extent in the Kara Sea and the Barents Seas in Winter on the Winter Monsoon Over East Asia

  Wu Bingyi, Huang Ronghui, Gao Dengyi

  1999,23(3):267-275, DOI: 10.3878/j.issn.1006-9895.1999.03.02

  Abstract (8624) HTML (0) PDF (0.00 Byte) (6126)

  Abstract:通过大量的数据分析发现，冬季喀拉海、巴伦支海海区是影响东亚以及北半球气候变化的关键区之一，该海区海冰面积变化与大气500 hPa高度场的EU遥相关型以及东亚冬季风强、弱之间存在密切的关系。冬季该海区海冰偏多，则500 hPa高度场容易出现EU遥相关型（日本及西欧500 hPa高度场偏高），亚洲大陆上的冷高压减弱，而北太平洋海域海平面气压升高，致使东亚冬季风偏弱以及2月份入侵我国的冷空气次数减少；而冬季该海区海冰偏少时，情况正好相反。

• Separation of Truncation Error and Round-off Error in the Numerical Integration and Its Validation

  Wang Pengfei, Huang Ronghui, Li Jianping

  2011,35(3):403-410, DOI: 10.3878/j.issn.1006-9895.2011.03.02

  Abstract (8604) HTML (0) PDF (403.54 K) (6700)

  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.

• The Seasonal March of the North Pacific Oscillation and Its Association with the Interannual Variations of China's Climate in Boreal Winter and Spring

  Wang Lin, Chen Wen, Fong Soikun, et al

  2011,35(3):393-402, DOI: 10.3878/j.issn.1006-9895.2011.03.01

  Abstract (8551) HTML (0) PDF (4.18 M) (7455)

  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.

• Research on the Earth System Dynamic Model and Some Related Numerical Simulations

  ZENG Qingcun, ZHOU Guangqing, PU Yifen, et al

  2008,32(4):653-690, DOI: 10.3878/j.issn.1006-9895.2008.04.01

  Abstract (8522) HTML (0) PDF (13.53 M) (15833)

  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。

• Interdecadal and Interannual Variabilities of the Asian Summer Monsoon and Its Projection of Future Change

  DING Yihui, SUN Ying, LIU Yunyun, SI Dong, WANG Zunya, ZHU Yuxiang, LIU Yanju, SONG Yafang, ZHANG Jin

  2013,37(2):253-280, DOI: 10.3878/j.issn.1006-9895.2012.12302

  Abstract (8383) HTML (0) PDF (7.98 M) (11858)

  Abstract:The present paper presents a concise summary of our studies on interdecadal and interannual variabilities of the Asian summer monsoon and its projection for recent five years, which can be summarized in the following three aspects:
  1) A significant interdecadal weakening of the Asian summer monsoon was identified on the basis of our analysis of a 123-year precipitation dataset in China and studies made by Indian investigators. This variability has caused significant changes in summer precipitation patterns in both East and South Asia. In East Asia, the main monsoon precipitation belt has continuously retreated southward, leading to a precipitation pattern of droughts in North China and floods in South China. The interdecadal change in the preceding winter and spring over the Tibetan Plateau and the sea surface temperature anomaly (SSTA) of the tropical central and eastern Pacific, in addition to the resulting land-sea thermal contrast, are the main drivers for the weakening of the Asian summer monsoon. In the future, the responses of the South and East Asian summer monsoons to a warmer climate will differ, with a continuous weakening in the former and enhanced circulation and precipitation fields in the latter.
  2) The interannual variability is mainly characterized by biennial and four-seven-year oscillations. The present paper focuses on formative processes, mechanisms and influences of tropospheric biennial oscillation (TBO) on precipitation in East Asia. The formation and cycle processes of two particular TBO modes, the Yangtze River Valley (YRV) and the Huaihe River Valley (HRV) modes, have been examined.
  3) On the basis of previous studies of teleconnection modes in the Asian monsoon region, we suggest the occurrence of low-level teleconnection types propagating along a strong monsoonal airflow belt from South Asia or the western North Pacific to East Asia. Such teleconnection types can exert an important effect on the Meiyu/Baiu season and summer precipitation in North China and Northeast Asia.
  Finally, it is indicated that global warming will have a more significant effect on the Asian summer monsoon in this century. Therefore, both anthropogenic and natural forcing are important factors in the long-term variation of the Asian summer monsoon.

• An Overview on Tropical Cyclone Research Progress in China during the Past Ten Years

  Chen Lianshou, Meng Zhiyong

  2001,25(3):420-432, DOI: 10.3878/j.issn.1006-9895.2001.03.11

  Abstract (8352) HTML (0) PDF (0.00 Byte) (10216)

  Abstract:90年代初，国内外开展了几次大规模的热带气旋现场试验，取得了许多宝贵的加 密观测资料。利用这些资料，对热带气旋尤其是异常热带气旋开展了一系列的研究。我国科学家在国家科技攻关85-906项目中的“台风科学、业务试验和天气动力学理论的研究”等与热带气旋有关的课题和国际热带气旋研究合作项目“SPECTRUM(SpecialExperimentConcerningTyphoonRecurvatureandUnusualMovement)”中对台风的突变现象和预报技术进行了重点研究。从而在过去10年中，在台风运动突变、结构和强度突变、台风暴雨的突然增幅、热带气旋路径预报方法研究等方面都取得了新的进展。作者将对这些进展作简要综述。

• The Instability of the Interannual Relationship between ENSO and the Summer Rainfall in China

  Zong Haifeng, Chen Lieting, Zhang Qingyun

  2010,34(1):184-192, DOI: 10.3878/j.issn.1006-9895.2010.01.17

  Abstract (8317) HTML (0) PDF (2.75 M) (6309)

  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.

• Analyzing Seasonal Variation of Clouds over the Asian Monsoon Regions and the Tibetan Plateau Region using CloudSat/CALIPSO Data

  WANG Hui, LUO Yali, ZHANG Renhe

  2011,35(6):1117-1131, DOI: 10.3878/j.issn.1006-9895.2011.06.11

  Abstract (8289) HTML (0) PDF (4.62 M) (6625)

  Abstract:Using the CloudSat/CALIPSO data products during the period of September 2006－August 2009, seasonal variations of cloud properties （including occurrence frequency, vertical location, physical thickness, distance between cloud layers, and vertical distribution of radar reflectivity) are contrasted among four regions: East Asian Monsoon Region（EAMR), Indian Monsoon Region（IMR), the Western North Pacific Monsoon Region（WNPMR), and the Tibetan Plateau Region（TPR). The geographical distribution of low-level clouds over the Asian monsoon regions and its correlation with atmospheric stability of the lower troposphere（LTS) are also analyzed. The major findings are as follows:（1) During the period, the total cloud amounts are 69% （EAMR), 72%（IMR), 83%（WNPMR), and 69%（TPR), respectively, to which single-layer clouds contribute 56%（IMR and WNPMR) to 77%（TPR). The multi-layer clouds are mostly double-layered or triple-layered（fractions≥95%). In the IMR, the total cloud amount in summer （greater than 90%) is significantly larger than in winter（about 50%); the total cloud amounts are larger during spring and summer（>90%) than autumn and winter（about 50%) in the EAMR and TPR; the seasonal variation is negligible over the WNPMR.(2) Clouds located above 10 km containing small ice crystals prevail in the tropical monsoon regions （IMR and WNPMR) all the year round. Marine boundary layer clouds are common during each season in the WNPMR, in contrast to the IMR where low-level clouds occur mainly during summer. The EAMR clouds are located mostly below 10 km from autumn to spring. Although more clouds are present in the upper troposphere during summer than other seasons over the EAMR, their occurrences and vertical locations are lower than those in the IMR and WNPMR（cloud amount of 60%－70% from 12 to 16 km heights). The TPR clouds are mostly located in the height range of 4－11 km, with cloud particles at the same height covering a wide range of size.(3) The geographical distributions of low-level clouds in the Asian monsoon region are similar between spring and autumn, and significantly distinct between summer and winter. Low-level clouds are the most abundant during winter（45%－70%), located mainly in the western North Pacific, southern Chinese mainland and the oceans to its east, and the regions around Japan. The low-level cloud amount is correlated with LTS quite well except for winter.(4) The cloud layers are geometrically thin in the four regions, with 30%－36% being thinner than 1 km. Moreover, the vertical distance between two consecutive layers in multilayered clouds with values less than 1 km accounts for about 10%. Both suggest a need to improve the vertical resolution of current general circulation models.