Current Issue

• Progress of the Evolutionary Characteristics of Autumn Rain in Western China and Its Anomalous Mechanism for the Past 20 Years
• Yinuo LI, Yueqing LI
• 2024 Vol. 43 (1): 1-15.  DOI:10.7522/j.issn.1000-0534.2023.00028
• Abstract ( ) PDF (1341KB) ( )

• Autumn rain in western China is a unique and complex precipitation phenomenon that takes place during the autumn season in the western region of China， which is closely related to various aspects of economy， society and human life.This natural phenomenon has a profound impact on agriculture， transportation and other aspects of social production and life， sometimes even causes the phenomenon of autumn flood， which deserves full attention.Based on the basic understanding of the phenomenon in the 20th century， this paper compares and reviews the main research achievements of autumn rain in western China over the past 20 years from multiple perspectives.First of all， the spatial distribution range and temporal extent and precipitation intensity of autumn rain in West China are thoroughly explored， quantitative criteria and indexes such as ARI （Autumn Rain Index）， DARI （Daily Autumn Rain Index） and MARI （Modified Autumn Rain Index）are also proposed.In addition to this， the significant interannual differences， the "positive - negative - positive" interdecadal variations and the 4~8 years cycle of autumn rain in western China fully demonstrate its complexity and inhomogeneity.Secondly， the different but important influences of atmospheric circulation systems at low， middle， and high latitudes， tropical sea temperature forcing including Pacific Ocean， Indian Ocean， and Atlantic Ocean as well as the Qinghai-Xizang （Tibet） Plateau effect and other aspects on the autumn rain in western China are pointed out.These different factors all play significant roles in the evolution of the phenomenon， but the mechanisms are different.This leads to the recognition of the significance of the multi-system and multi-factor synergistic effect on the anomalous evolution of autumn rain in western China， which enriches the understanding of the autumn rain and its impact.Finally， according to the current cognition of autumn rain in western China， the main problems that exist in the combination of different monsoon systems like Indian monsoon， East Asian monsoon and Plateau monsoon， cold and warm air currents， evolution causes， weather processes， night rain characteristics， regional responses to the global warming and other aspects are pointed out.These problems highlight the challenges that researchers face in studying this complex phenomenon.However， despite the challenges， there are several promising areas for future research.The main development trend in the future about the research of autumn rain in western China is the comprehensive and elaborate analysis of the multi-scale synergy of autumn rain in western China and its physical mechanism under the complex and important topography of Qinghai-Xizang （Tibet） Plateau.

• Review on Developments and Improvements in Vertical Coordinates for Numerical Prediction Models
• Rui CHENG, Rucong YU, Youping XU, Jing HUANG, Xiaojing SHEN
• 2024 Vol. 43 (1): 16-27.  DOI:10.7522/j.issn.1000-0534.2023.00042
• Abstract ( ) PDF (846KB) ( )

• As we know， the atmosphere is mainly characterized by its baroclinicity and stratification.The vertical coordinate is crucial for the description of 3D atmospheric motion and thermal-dynamic condition of the static atmosphere.Furthermore， the vertical coordinate is foundation of numerical prediction model construction.Different atmospheric dynamic cores， such as height， pressure and potential temperature-based frames are usually established depending on different vertical coordinate modes.The development of vertical coordinates always contributes to major version update and considerable upgrade of the numerical prediction model.In this paper， we briefly review the history of vertical coordinates for the numerical model.Then， we mainly demonstrate the design art for hybrid vertical coordinates in some operational non-hydrostatic models at home and abroad.Additionally， this paper presents some suggestions on how to select model vertical resolution and prediction variables vertical distribution style.Finally， the progress on arrangement and application of the vertical coordinate for numerical prediction models is summarized and its development tendency is also illustrated.

• A Comparative Study on the Summer Raindrop Size Distribution Among Areas over the Central and Eastern Qinghai-Xizang （Tibetan） Plateau and the Western Sichuan Basin
• Yanxia LIU, Jun WEN, Xiaolin XIE
• 2024 Vol. 43 (1): 28-41.  DOI:10.7522/j.issn.1000-0534.2023.00033
• Abstract ( ) PDF (7079KB) ( )

• To promote the understanding of precipitation microphysical characteristics and differences in the central and eastern Qinghai-Xizang （Tibetan） Plateau and the Sichuan Basin， disdrometer measurements collected at Naqu， Yushu， Linzhi， Batang， Luding， and Chengdu from July to August 2019 and 2020 are utilized to comprehensively investigate the characteristics and differences of raindrop size distributions （RSDs） among the six different areas.Meanwhile， local empirical relations between the Gamma shape parameter and slope parameter and between the reflectivity factor and rain rate are proposed and compared.The results show that RSDs in the basin and adjacent areas （Chengdu and Luding） are generally wider and have higher number concentrations of medium-to-large raindrops （diameter ≥1.0 mm） than those in the plateau areas （Naqu， Yushu， Linzhi， and Batang） due to the contribution of more strong convective precipitation.In contrast， RSDs in the plateau areas are narrower and possess higher number concentrations of small raindrops （diameter <1.0 mm） due to more occurrences of stratiform and weak-convective precipitation.RSDs gradually become wider with higher number concentrations as the increase of rainfall intensity both in the six observation areas.The RSD differences among the six observation areas can also change with the rain rate.Specifically， when the rain rate exceeds 0.1 mm·h^-1， the increase of the number concentration of small raindrops with increasing rain rate is significantly greater in Naqu and Linzhi than in other areas， and can gradually exceed that in Chengdu.When the rain rate exceeds 5 mm·h^-1， the differences in the number concentrations of medium-to-large raindrops between Chengdu and Luding and other plateau areas also gradually become larger.With the same shape parameters， the slope parameters in Chengdu and Luding are smaller than in other areas， indicating that they possess a slower decreasing rate of raindrop number concentration with increasing particle size than that in other plateau areas.Under the same radar echo intensities （reflectivity factor）， rain rates of stratiform precipitation in Naqu and Linzhi are greater than in other regions.The rain rate of convective precipitation in Linzhi is also greater than that in other areas when the radar echo is below 40 dBZ， but the rain rate of convective precipitation in Naqu can be smaller than that in other areas when the radar echo is greater than 40 dBZ.

• Action Mechanism of Tibetan Plateau’s Eastern Slope Topography on the PLV Affecting Yunnan Precipitation
• Yu HE, Li ZHU, Guoping LI, Jiaxu XIE, Wenqian MA, Li TAO, Wanchen ZHANG
• 2024 Vol. 43 (1): 42-58.  DOI:10.7522/j.issn.1000-0534.2023.00037
• Abstract ( ) PDF (9357KB) ( )

• Using radiosonde and ground mapping data from conventional observations， FNL analysis data （1°×1°） and quality controlled hourly precipitation data of Yunnan regional automatic station， diagnosed the function of the Qinghai-Xizang Plateau’s eastern slope topography in the PLV （plateau vortex） affected precipitation in Yunnan during 2-3 July 2017.While the latest WRFv4.0 numerical model is used to conduct the topographic sensitivity test of this process.The results show that PLV which generated in the Yajiang region of Sichuan province （NO.C1735） is an important system influenced on this heavy rainfall in Yunnan； This low-vortex system maintain warm core structure in the middle and high altitude during the process period， corresponding with remarkable alternately distribution of ascending and descending movements； Distribution of process accumulated rainfall present two obvious NW-SE rain belts parallel to the mountain trend and the precipitation on the rain belt have intensity interlaced fluctuation characteristics； The heavy rainfall mainly occurred within two periods： one from afternoon to evening and other at the first half of the night， and all located besides the terrain slope （the east and south slopes）， especially in areas with steep terrain， large slopes， and trumpet-shaped topography， and then propagates downstream alone with the PLV； The South Asian High， northwest divergent airflow， Western Pacific subtropical high and Yunnan-Myanmar high provides favorable upper flow field for the eastward movement and development of the PLV， besides the position of 500 hPa positive vorticity and 700 hPa water vapor flux convergence can well indicates the heavy rainfall area； There exist β-mesoscale gravity wave during the period of precipitation， which stimulated by the Qinghai-Xizang Plateau’s eastern slope， and propagate between 300~200 hPa； Non geostrophic equilibrium motion and vertical wind shear at high-altitude are beneficial to the occurrence and propagation of gravity wave； The gravity wave propagate downstream before the PLV and precipitation， its wave ridge corresponds to the upward motion and divergence center， whereas the wave trough corresponds to the descending motion and convergence center， the heavy precipitation and the wave ridge are all located at the southwest side of PLV， the area of strong convergence and upward movement； After reduced the terrain height， its mechanical blocking and lifting effect weakened， the gravity wave and PLV disappears， leading to significant changes in the intensity and spatial distribution of the rain belt； Thus， the topography of the eastern slope of the Plateau plays important role both on the formation and development of PLV and precipitation in Yunnan under the influence of PLV.

• Multi-Scenario Projection of Future Precipitation over the Qinghai-Xizang （Tibetan） Plateau Based on CMIP6 Model Assessment Results
• Boyuan LI, Qin HU
• 2024 Vol. 43 (1): 59-72.  DOI:10.7522/j.issn.1000-0534.2023.00029
• Abstract ( ) PDF (9440KB) ( )

• As a climate-sensitive region， precipitation over the Qinghai-Xizang （Tibetan） Plateau significantly impacts the water cycle and the climate of East Asia.Therefore， it is important to study its changes.Precipitation is an important variable in the global hydrological cycle and one of the major climate systems affected by climate change.To investigate the ability of the global climate models to simulate precipitation over the Qinghai-Xizang （Tibetan） Plateau and examine possible changes in future precipitation under the new model and scenarios， this paper uses the latest monthly precipitation data from the 31 climate models of the Coupled Model Intercomparison Project 6 （CMIP6） and the CN05.1 precipitation observation data set provided by the National Climate Center to evaluate the ability of the CMIP6 model to simulate precipitation over the Qinghai-Xizang （Tibetan） Plateau.Furthermore， better models are selected to project the future precipitation of the Qinghai-Xizang （Tibetan） Plateau under different Shared Socioeconomic Pathway （SSP） scenarios.The results show that the model distribution of observed precipitation over the Qinghai-Xizang （Tibetan） Plateau from 1995 to 2014 is characterized by a decrease from southeast to northwest and a summer precipitation concentration.Most of the models can simulate the precipitation distribution and seasonal trend， but almost all of them overestimate the precipitation phenomenon， and the average precipitation of multiple modes is 102% higher than that observed.In general， the latest model of CMIP6 has a poor ability to simulate precipitation over the Qinghai-Xizang （Tibetan） Plateau， and the average relative deviation index of the model from the observation is 102%， indicating that most of the models are not satisfactory， and EC-Earth3-Veg-LR， MPI-ESM1-2-LR， EC-Earth3-Veg， and MRI-ESM2-0 are selected as the better modes after quantitative analysis of all the models， which can roughly reflect the precipitation characteristics of the Qinghai-Xizang （Tibetan） Plateau.Climate models show the slowest increase of precipitation over the Qinghai-Xizang （Tibetan） Plateau under the SSP1-2.6 scenario and the fastest increase under SSP5-8.5.From SSP1-2.6 in the small radiative forcing scenario to SSP5-8.5 in the large scenario， the recent （from 2021 to 2040） precipitation increase on the plateau is difficult to find a large difference in each scenario， but there is a significant increase in the mid （from 2041 to 2060） and late （from 2081 to 2100） scenarios， indicating that carbon emission intensity has a small impact in the short term and a large impact in the long term.The future increase in precipitation mainly occurs in the area south of the Nianqing Tanggula Mountains， from a seasonal point of view， the summer increase is the largest， followed by spring and autumn， the smallest increase is in winter， so we should pay attention to the future summer and spring precipitation changes over the Qinghai-Xizang （Tibetan） Plateau and take coping measures.

• Analysis of the Dynamical Structure and Genesis of Two Different Life-History Eastward Moving Plateau
• Nini TU, Shuhua YU, Yueqing LI
• 2024 Vol. 43 (1): 73-87.  DOI:10.7522/j.issn.1000-0534.2023.00048
• Abstract ( ) PDF (24025KB) ( )

• The NCEP reanalysis data were utilized to diagnose the structural characteristics and evolutionary mechanisms of two plateau vortex processes that moved eastward out of the plateau on June 25-27， 2008 and June 4-10， 2013.The data were also used to explore the structural characteristics of the two long and short track plateau vortex processes and the influencing factors that caused their different life histories.The results show that： （1） During the Zhaduo vortex activity with a short path， the South Asian high pressure is flattened， the upper-level jet stream is southward and the plateau vortex moves out of the plateau in the slump trough.During the Qumalai vortex activity with a long path， the South Asian high pressure has a north arch， the plateau vortex is in the northwest airflow under the South Asian high-pressure ridge， the subtropical high is southward and the plateau vortex is strengthened with the eastward movement of the trough， accompanied by the eastward movement of the southwest vortex.（2） The two plateau vortex processes exhibit distinct structural characteristics， especially when the Zhaduo vortex is strengthened on the plateau and when the Qumalai vortex is strengthened again after coupling with the southwest vortex.The former vortex is in the deeper positive vorticity and upward motion layer at 600~350 hPa and also has the structural characteristics of strong divergence in the upper troposphere.The latter has the structural characteristics of high， middle， and low positive vorticity penetration in the troposphere， ascending movement in the troposphere， and weak divergence in the troposphere.（3） The diagnosis of total vorticity budget shows that the change of divergence term plays a decisive role in the change of total vorticity variability of low vortices.The strength change of Zhaduo vortex is consistent with the divergence term change.The influence of vertical transport term and horizontal advection term are strengthened during the accompaniment of Qumalai vortex with the southwest vortex.（4） Regarding the budget analysis of the 500 hPa positive vorticity variability in the central region of the vortex， the results show that when there is no activity of the southwest vortex， the plateau vortex contributes mainly to the 500 hPa positive vorticity variability of the plateau vortex due to convergence.When there is activity of the southwest vortex， the vertical transport of positive vorticity becomes more important with the superposition and companionship with the southwest vortex in the vertical direction.

• Evaluation of Winter Near-surface 2 m Temperature around the Hengduan Mountains in Southwest China Simulated by ECMWF
• Shimei WU, Na TANG, Yuqi LIANG, Xuyang OU, Haijie LI, Haoming CHEN
• 2024 Vol. 43 (1): 88-98.  DOI:10.7522/j.issn.1000-0534.2023.00049
• Abstract ( ) PDF (7805KB) ( )

• Based on the hourly product of CLDAS （CMA Land Data Assimilation System） in 2021， this study is to evaluate the prediction capacity of the global high-resolution deterministic numerical prediction product ECMWF （European Center for Medium Weather Forecasting） for winter mean near-surface 2 m temperature of complex terrain region around the Hengduan mountains in southwest China by starting from winter average temperature， daily variation， and diurnal temperature range.And this study compares the temperature deviation characteristics of near-surface 2 m temperature in different topographic regions by distinguishing between high terrain region （the Western Sichuan Plateau） and low terrain region （the southern Sichuan Basin）.The results show that： （1） The ECMWF model can reasonably predict the spatial distribution characteristics of the winter mean near-surface 2 m temperature around the Hengduan mountains in southwest China， but the deviation distribution is related to the terrain height.With the increase of the terrain height， the prediction deviation tends to increase.（2） The ECMWF model well reproduces the daily variation characteristics of winter mean near-surface 2 m temperature around the Hengduan mountains in southwest China， with the peak time appearing at 14:00 （Beijing Time）.The prediction deviation of temperature at various times varies at different terrain heights.The maximum negative deviation of the western Sichuan Plateau and the Hengduan mountain regions occurs in the afternoon， while the maximum negative deviation of the south Sichuan Basin occurs in the morning.At the same time， the prediction deviation at each moment in high terrain areas is greater than the prediction deviation at each moment in low terrain areas.（3） The ECMWF model can reasonably predict for the spatial distribution of winter mean near-surface 2 m temperature over different terrain at various times during the day， but the deviations have diurnal variation characteristics.Especially in the high terrain region of the Hengduan mountain regions， there are different characteristics of cold and warm deviations at various times.（4） The area with large forecast bias of diurnal temperature range is generally the area with frequent Quasi-stationary front activities in Kunming.For the days （A total of 90 days， from December 1， 2021 to February 28， 2022） with large diurnal temperature range， the prediction deviation of winter mean near-surface 2 m temperature in this area is greater than the days with small diurnal temperature range.What’s more， the prediction deviation of diurnal temperature range is relatively unstable in the area with large forecast bias of diurnal temperature range.

• Study on Precipitation Observation and Retrieval Methods of X-band Phased Array Polarization Weather Radar in Motuo， Xizang
• Haoran CHEN, Fei GENG, Liping LIU, Hua YANG
• 2024 Vol. 43 (1): 99-113.  DOI:10.7522/j.issn.1000-0534.2023.00039
• Abstract ( ) PDF (8650KB) ( )

• The variation in precipitation in Motuo is closely associated with the transport of water vapor from the India Ocean and the Bay of Bengal to inland China， the Asia summer monsoon， and the progression of the rain band in eastern China.A rain band with an average annual precipitation of more than 2000 mm has been formed due to the interaction of the distinctive topography of Motuo and the southwest air flow.However， it has been challenging to observe precipitation in Motuo due to the peculiar topography， insufficient electricity， and inadequate traffic conditions.An X-band dual-polarization phased array radar （XPAR） is installed during the Second Qinghai-Xizang Plateau Scientific Expedition and Research Program.The advanced dual-polarization phased array radar is used to continuously observe the precipitation in Motuo and is of great significance to the research of the local ecological environment and cloud water resources， and the impact on downstream.Based on XPAR data collected for the period from June to August 2020， we selected the radial precipitation echoes using a statistical method， and after integrating the precipitation echoes， we created the hybrid elevation angle that tallied with the topography of Motuo.Using DSD data from Motuo in 2019， we calculated radar parameters and obtained the localized QPE （Quantitative Precipitation Estimation） formulas of X-band weather radar.We selected three processes of precipitation with different cumulative precipitation， duration， and average rain rate from July to August 2020， calculated Φ _DP （Differential Propagation Phase Shift） using the linear programming method， K _DP （Differential Propagation Phase Shift Rate） using the ordinary least square method， and corrected Z _H （Reflectivity Factor） using the “ZPHI” rain profiling algorithm.Using Z _H and K _DP as thresholds， we estimated precipitation piecewise utilizing R（Z _H） and R（K _DP）， and contrasted results with the QPE results from the R（Z _H） and R（K _DP） methods， respectively.And explored the relationship between precipitation distribution and the topography of Motuo based on the QPE results.The quality of Z _H and K _DP had been significantly improved.The hybrid elevation angle constructed using a statistical method had a larger echo area than the hybrid elevation angle constructed using STRM1 v3.0 data.The PPI （Plane Position Indicator） diagrams of three precipitation （radar parameters at typical times， and average radar parameters） processes can show the relationship between the variation in precipitation and the topography of Motuo.The QPE formulas and Piecewise Estimation Method （PEM） used in the research functioned well， and each evaluation parameter performed well.The following conclusions are drawn： （1） The hybrid elevation angle constructed using the statistical method outperformed the hybrid elevation angle constructed using topography data in QPE， due to the drastic variation of the topography around the XPAR in Motuo； （2） The data quality control method， the QPE formulas， and the PEM utilized in the research all performed well at precipitation retrieval.The estimation error of the QPE results was significantly reduced， without causing significant changes in CC and RMSE； （3） Precipitation in Motuo may occur and grow as a result of the lifting of the southwest air flow by northern slopes of the valley.Clouds with higher rain rates and smaller drops are found near the level bottom of the valley.

• Analysis of Water Vapor Transport Reduction in the Yarlung Tsangpo Grand Canyon Region： a Trajectory Tracking Approach
• Dengxv ZHANG, Hongru YAN, Yunfei MIAO, Min ZHANG
• 2024 Vol. 43 (1): 114-126.  DOI:10.7522/j.issn.1000-0534.2023.00050
• Abstract ( ) PDF (3953KB) ( )

• The Yarlung Tsangpo River Grand Canyon region serves as a main water vapor entrance for the Tibetan plateau.However， the region has been experiencing a persistent decline in both water vapor convergence and precipitation since 1979， which has an important impact on the water storage over the Tibetan Plateau.In order to investigate the reasons behind this reduction in water vapor transport in the area， ERA5 hourly reanalysis data were utilized to drive the LAGRANTO model to derive the backwards water vapor transport trajectories in the region during the boreal summer （June to August） of typical dry and wet years， facilitating a comparative analysis of alterations in moisture flux along these trajectories.It was found that the water vapor sources primarily originating from four oceanic regions： the Bay of Bengal in the southern plateau， the Arabian Sea on the southwest side of the plateau， the Indian Ocean around south of the equator， and the South China Sea.The water vapor transportation in these regions is predominantly governed by the South Asian and Indian summer monsoons and influenced by the Somalia cross-equatorial jet.By comparing the characteristics of water vapor transport trajectories in dry and wet years， it is evident that trajectory patterns remain largely unchanged， with the exception of the South China Sea source.Furthermore， moisture flux along these trajectories diminishes as elevation increases， and the moisture loss during wet years consistently proves to be lower than that during dry years.Additionally， the trajectories originating from the Bay of Bengal source are supplemented by water vapor from the ocean surface， resulting in significant increased water vapor flux in wet years.This finding is supported by comparing the evaporation， precipitation， and circulation fields between dry and wet years.Ultimately， during wet years， the moisture flux reaching the boundaries of the Yarlung Tsangpo Grand Canyon region surpasses that of dry years， notably marked by a particularly significant increase in moisture entering through the southern boundary.This highlights that the depletion processes during water vapor transport， in addition to contributions from moisture sources and the influence of large-scale monsoonal circulation， play a critical role in determining the moisture equilibrium within the Yarlung Tsangpo Grand Canyon region.

• Mesoscale Numerical Simulation and Cloud Microphysical Characteristics of the Warm Zone Blizzard in Northern Xinjiang
• Anbei LI, Chenxiang JU, Yaman ZHOU, Man LI, Ruqi LI
• 2024 Vol. 43 (1): 127-140.  DOI:10.7522/j.issn.1000-0534.2023.00040
• Abstract ( ) PDF (12108KB) ( )

• The warm zone blizzard are both infrequent and highly destructive， making their accurate prediction a challenging and crucial focus.This study utilized four distinct cloud microphysics schemes （Lin， Thompson， WDM6， and WSM6） within the WRF mesoscale model to conduct a numerical simulation of a typical warm zone blizzard process in the northern Xinjiang in the middle of November 2016.The research objectives encompassed the evaluation of the model's capacity to simulate the warm zone blizzard， the selection of an optimal parameterization scheme， an analysis of the vertical distribution and evolution of hydrometeors during the snowstorm， and an exploration of the developmental patterns of related mesoscale systems contributing to the snowstorm.The analysis yielded the following key findings： （1） Among the diverse cloud microphysics parameterization schemes tested， the Lin scheme demonstrated the most favorable performance， effectively simulating snowfall magnitudes， spatial distributions， and trends.（2） In the cloud， all kinds of water condensate particles are active in the lower and middle troposphere， with graupel and snow being the most.Ice crystals， snow， cloud water and graupel particles are distributed from the upper layer to the lower layer.Near the windward slope of Altai Mountain is the center of the large concentration of each water condensate particle.The vertical alignment of the high value center of the four kinds of cloud water condensate particles in the strong snowfall area is conducive to the transformation of each particle.（3） High-humidity systems upstream moved westward， with the intensification of low-level southward jet streams resulting in pronounced moisture convergence.The western foothills of the Altai Mountains acted as a barrier， promoting moisture convergence by blocking the windward side； The low-level southerly jet also provides a continuous updraft and unstable condition for the generation of the blizzard.Strong snowfall is located in a wide updraft area between two groups of secondary circulations.The explosive growth of vertical movement is conducive to triggering the release of unstable energy， providing strong dynamic lifting conditions for the development and maintenance of the blizzard.

• Analysis of Water Vapor Characteristics During Heavy Snow in Different Warm Regions of Northern Xinjiang
• Xiaocui ZHUANG, Lijuan CHEN, Boyuan LI, Yunlin MIAO
• 2024 Vol. 43 (1): 141-155.  DOI:10.7522/j.issn.1000-0534.2023.00041
• Abstract ( ) PDF (9137KB) ( )

• This thesis analyzed the data with NCEP/NCAR method， took HYSPLIT （Lagrangian forward trajectory） method to simulate water vapor characteristics of 27 winter snowstorms in northern Xinjiang from 1980 to 2020， and also analyzed the source-sink relationship of water vapor in different regions and its contribution to blizzard.The results show that the main 500 hPa water vapor source is from Greenland， the Atlantic Ocean and its coast， the Mediterranean Sea， as well as the Black Sea and its vicinity.The water vapor source contributing the most to the blizzard in Altay region is from the Atlantic Ocean and its coastal area， the water vapor source contributing the most to the blizzard in Ta'e Basin is from the Mediterranean Sea， the Black Sea and its vicinity， and the losses along the way are great.700 hPa water vapor source is mainly from northern Europe， the Atlantic Ocean and its vicinity， the Mediterranean Sea， as wll as the Black Sea and its vicinity.The water vapor source contributing the most to the blizzard in Altay is from the Mediterranean Sea， the Black Sea and its vicinity， and the greatest losses are in and around the Mediterranean Sea and the Black Sea； the water vapor source contributing the most to the Ta'e basin is from northern Europe， and the greatest losses are in the Atlantic Ocean and its coasts.850 hPa water vapor source is mainly from Central Asia the Mediterranean Sea， the Black Sea and its vicinity， the former contributed the most to blizzard.After reaching the blizzard area， the water vapor increases.The water vapor in each source reaches the key lizzard areas with the westerly air flow， mainly from the west （southwest） and northwest， and the former path is dominant； The source and path of water vapor in Altay area of lower troposphere are more complicated than that in Ta'e Basin.Based on the above analysis， the contribution model of water vapor source and path of snowstorm in warm area was constructed， and the water vapor contribution of each layer in Altay area and Ta'e Basin was described in detail.

• Analysis on Precipitation Extremes and Characteristics of the Rainstorm Event in the West of Hexi Corredor
• Junxia ZHANG, Wubin HUANG, Yicheng WANG, Yanqin ZHAO, Jixin WANG
• 2024 Vol. 43 (1): 156-165.  DOI:10.7522/j.issn.1000-0534.2023.00036
• Abstract ( ) PDF (4096KB) ( )

• An extremely heavy rainstorm occurred 20:00 on 12 to 20:00 （Beijing Time） on 13 August 2022 in Jinta， Gansu Province， the 24 hours cumulative precipitation and hourly precipitation at Jinta station broke the historical extreme values.Based on the minutely， hourly and daily precipitation observation data， as well as the CMA Multi-source Merged Precipitation Analysis System （CMPAS） hourly precipitation data， the precipitation characteristics and extremity of the torrential rain event were analyzed.The results show that the extremely torrential rain event is characterized by large cumulative precipitation， strong locality， strong short-term precipitation and obvious convection.The main precipitation period is night and the rainstorm center is located in Jinta county， Jiuquan city.There are 11 stations reached the maximum since the station establishment， among which， the maximum appeared in Jinta station， reaching 88 mm， which is the second largest observed of all national stations in Jiuquan city， exceeding 58% of the historical average of the flood season in 62 years （from 1961 to 2022）.There are 13 stations’s hourly precipitation reached the maximum since the station establishment and the maximum hourly precipitation of Jinta station was 56.2 mm， ranking the first among all the stations in Jiuquan， nearly three times of the average rainfall in August in Jinta Station in the past 62 years， showing obvious historical extremes.There are three precipitation periods in Jinta Station， and the heavy precipitation mainly occurs in the second period， with strong minutely precipitation intensity and long duration.The heavy precipitation center first appeared in the southeast of Jinta station， and then moved to the northwest， with the range of heavy precipitation expanding.After three hours， the precipitation intensity weakened and moved out to the southeast， and the precipitation process in the rainstorm area ended.

• Analysis of Atmospheric Environment Characteristics and Radar Characteristics of Three Short-time Heavy Precipitation Cases under Different Influence Systems in Central Yunnan
• Hong ZHOU, Ying MIN, Yanyan XU, Lijia NA, Hongwei YE
• 2024 Vol. 43 (1): 166-183.  DOI:10.7522/j.issn.1000-0534.2023.00046
• Abstract ( ) PDF (17769KB) ( )

• Based on conventional observation data， NCEP 1°×1° reanalysis data， hourly and 5min automatic station precipitation data， and CINRAD/CC Doppler radar data in Kunming， three short-time heavy precipitation cases under different influence systems during the main flood season of 2021 in central Yunnan are studied.The characteristics of precipitation， circulation pattern， atmospheric environment and structure， shape and evolution of radar echoes are compared and analyzed.The results show that the difference of the three short-time heavy precipitation cases is mainly due to the difference weather systems on 500 hPa.There are shear lines at 700 hPa， but the formation seasons are different.There are convergence lines or weak cold fronts on the ground.The environmental conditions of the three cases are consistent with those of other regions of China in terms of unstable stratification， water vapor near the ground and vertical wind shear， however， there are significant differences in the total precipitable water， CAPE， SWEAT index.The shape of convective echo includes dot echo， block echo， strip echo， flocculent echo and so on.Convective storm type can be divided into high-echo-centriod convective storm， low-echo-centriod convective storm and mixed-echo-centriod convective storm.Short-time heavy precipitation has a single stage of some convective storm type， also has several convective storm types appearing at the same time.CAPE and SWEAT index have a certain correlation with convective storm types.Strong echo profile is columnar structure or tower structure.35 dBz strong echo is grounded without overhang characteristics.Short-time heavy precipitation is mostly generated by long- time stagnant or slow-moving convective echo， some short-time heavy precipitation is also generated in the "train effect" of radar echoes.The duration of short-term heavy precipitation formed by monomer with short life cycle is mostly within 1h， but the duration of short-term heavy precipitation formed by monomer combination and repeated generation and extinction or "train effect" is usually 1~3 h.The instantaneous rain intensity produced by high-echo-centriod convective storm can reach more than 10 mm·（5min）^-1， while the rainfall intensity produced by low-echo-centriod convective storm and mixed-echo-centriod convective storm can range from 3~10 mm·（5min）^-1， and a few can reach more than 10 mm·（5min）^-1.

• Machine Learning-Based Prediction of Summer Extended-Range Precipitation and Possible Contribution of Soil Moisture over China
• Yuchen YE, Haishan CHEN, Siguang ZHU, Yinshuo DONG
• 2024 Vol. 43 (1): 184-198.  DOI:10.7522/j.issn.1000-0534.2023.00025
• Abstract ( ) PDF (9551KB) ( )

• Low accuracy of extended forecast remains an important scientific problem in the current stage， and qualified extended forecast is of great significance for disaster prevention and mitigation.In this study， the machine learning method was used to forecast the summer precipitation during the extension period （5~30 days） in China， and explore the possible contribution of soil moisture to extended forecast of precipitation.Based on the results， machine learning methods remarkably outweigh traditional linear models in terms of forecast accuracy， with Catboost， Lightgbm and Adaboost being the optimal machine learning methods.According to further analysis， the abnormal evaporation and sensible heat anomaly caused by the surface soil moisture anomaly in the Yangtze River Basin can lead to the atmospheric circulation and vertical movement anomaly， which eventually affects summer precipitation.The set of three optimal machine learning methods was applied to calculate the contribution rate of each forecasting factor in the model.It was found that the local soil moisture dominated the extended precipitation in the Yangtze River Basin from the 5th day to the 10th day， while the local soil moisture played a dominant role on previous precipitation from the 10th day to the 15th day， and the extended precipitation in the Yangtze River Basin during the period of Day 20~30 was basically controlled by large-scale circulation.Besides， the influence of non-local soil moisture on extended precipitation was evaluated， the results of which showed that the surface soil moisture in Indo-China Peninsula mainly contributed to the extended precipitation in the Yangtze River Basin from the 15th day to the 30th day.By adding the surface soil moisture of Indo-China Peninsula to the extended precipitation model in Northeast China， it was found that surface the soil moisture failed to improve the extended forecast accuracy of precipitation in this area， which verified the availability of the machine learning model.This study provides a certain reference for forecasting precipitation in the extended period and exploring the contribution rate of forecasting factors.

• Numerical Simulation Research on the Effect of Hail Suppression by AgI Seeding on Microphysical Process and the Charge and Discharge of Hail Cloud
• Xian LU, Fengxia GUO, Zeyi WU, Zhou LIU, Jie DENG, Ke CHEN, Qingyuan WANG
• 2024 Vol. 43 (1): 199-216.  DOI:10.7522/j.issn.1000-0534.2023.00026
• Abstract ( ) PDF (11817KB) ( )

• A hail process in Xunyi hail suppression experimental area of Shaanxi Province at 13:00 （Beijing Time） on 28 July 1997 was simulated by using a three-dimensional strong storm dynamic electric coupling numerical model.This paper analyzes the influence of artificial hail suppression on the concentration and temporal and spatial variation of ice particles in clouds， as well as its influence on electrification and discharge.The results show that， overall， the concentration and specific water content of ice crystals， snowflakes and graupel particles increase in the range of -40~0 ℃.AgI seeding reduces the average scale of graupel and greatly reduces the conversion ratio to hail， resulting in the reduction of specific water content and number concentration of hail.With the increase of AgI seeding dose， hail suppression effect will be better， but the rainfall will first increase and then decrease.Therefore， the seeding dose should take an appropriate value between balanced hail suppression and precipitation enhancement.AgI seeding will lead to the positive lower non-induced electrification zone appears earlier， the center is enhanced and the upper boundary is raised in the early stage， while in the late stage， the center of the negative upper non-induced electrification zone is enhanced.Therefore， the bottom sub-positive charge area was enhanced in the early stage after seeding， and the upper main positive charge area and the middle negative charge area were enhanced in the late stage.With the increase of catalytic dose， these changes became more obvious.AgI seeding has a certain inhibitory effect on ground lightning， but the cloud flash and total flash increase a little after seeding， the peak time of the first discharge and cloud flash is earlier， the discharge duration is stronger， and the lightning frequency is slightly reduced in the lightning frequent period.

• Effect of Downward Shortwave Radiation Difference on the Surface Radiation Balance of Meadow Grassland
• Fu LI, Bingrong ZHOU, Li WANG, Wenze MA, Jinhu HUO
• 2024 Vol. 43 (1): 217-226.  DOI:10.7522/j.issn.1000-0534.2023.00035
• Abstract ( ) PDF (2690KB) ( )

• Based on the 20%， 40%， 60% and 80% quantiles of the daily cumulative energy of downward shortwave radiation， the four-component radiation observation data observed by the Haibei Animal Husbandry Experimental Station of China Meteorological Administration from September 2014 to December 2020 were divided into five groups.The influence of difference in downward shortwave radiation on the radiation balance of meadow grassland has been analyzed， which provided a basis for clarifying the changes and causes of radiation balance under different sunlight conditions.The results show that the downward shortwave radiation energy in the whole year is 8192.9 MJ·m^-2·a^-1， which can be theoretically received under the condition of abundant sunlight.Under normal sunlight， it is only 80% of that in the condition of abundant sunlight， while this proportion is only 40% under the condition of less sunlight.The downward shortwave radiation received by the surface under different sunlight conditions showes a very significant logarithmic increase trend in the same month， and the difference between the groups exceeds the difference between different season.There are also large differences between the groups of upward shortwave radiation and atmospheric longwave radiation.However， the upward shortwave radiation increases with the increase of solar radiation， due to the change of air humidity and cloudiness， while the atmospheric longwave radiation decreases with the increase of solar radiation.The variation of surface longwave radiation under different sunlight conditions is small， and does not exceed 3%.Although the difference in surface longwave radiation is not significant between the three sunlight conditions， due to the small amount of downward shortwave radiation received under the condition of less sunlight， the surface longwave radiation is 3.4 times more than the downward shortwave radiation， while it is only 1.4 and 1.7 times under the other two lighting conditions.As the increase of sunlight， the net shortwave radiation received by the surface increases， and the net longwave radiation also increases.Therefore， the energy absorbed by the radiation under different sunlight conditions accounts for 36% to 39% of the downward shortwave radiation energy received in each case.In addition， the difference of sunlight conditions also affect the linear regression model between downward shortwave radiation and net total radiation.The coefficient of determination and slope of the relationship model are the smallest under the condition of less sunlight.The coefficient of determination of the relationship model are above 0.85 for both normal and abundant sunlight.However， the slope is 1 when the sunlight is normal， while the slope is 0.87 when the sunlight is abundant.

• Turbulent Flux Mass Evaluation and Contribution Region Analysis of the Underlying Surface in Southern Sichuan Forest
• Demin FAN, Yu ZHANG, Youqi SU, Qian ZHANG
• 2024 Vol. 43 (1): 227-240.  DOI:10.7522/j.issn.1000-0534.2023.00027
• Abstract ( ) PDF (8951KB) ( )

• As flux observations are susceptible to complex underlying surface and instrument accuracy， rigorous pre-processing and quality control of the raw data is required based on the principles of the Eddy Covariance system observations.In this study， turbulence observations of the eddy-related system from May to December 2021 were selected from the Si'e Mountain Forest in the southern Sichuan region， and the observations were set up at different heights， including within the rough sublayer， at the boundary between the rough sublayer and the normal flux layer， and within the normal flux layer.The variability of the turbulent flux calculations under the two coordinate rotation schemes is quantified by the above observations and the quality of the flux data series is evaluated in conjunction with turbulence stability and development tests.Finally， the range of variability of the flux contribution region represented by the footprint function is analyzed for different atmospheric stability and different observation heights.The results show that the flux data corrected by the double coordinate rotation are larger than those from the plane fit and that the difference in correction between the two is significant with increasing observation height.Regarding flux data quality features， sensible heat flux data quality is better than latent heat flux and CO₂ flux， and lower data quality is better than higher data quality.At observation heights of 38 m and 56 m， the dominant wind direction showed opposite day and night variations in northeast-northwest direction， especially from May to September.There is some variation in the range of flux contributions at different levels of atmospheric stability.Under atmospheric stability， 80% of the flux information at 38 m altitude comes from the area 50~1400 m west of the tower； under atmospheric instability， the horizontal range of the source area for flux measurements is between 0 and 500 m.At an observation height of 56 m and under stable atmospheric conditions， the boundary of the source area with 80% flux contribution can be up to 1500 m from the measurement point； under unstable conditions， the source area lies between 0 and 750 m.There is a significant difference in the size of the contribution zone between winter and summer under stable atmospheric conditions， with the maximum turbulent flux information coming from 1320 m and 700 m in summer and winter respectively at an observation height of 38 m.The distribution of the flux contribution zone is influenced by the observation height for the same atmospheric stability， with the flux source zone at 56 m observation height being larger than the flux source zone at 38 m.

• Optical Characterization of Aerosols in Gansu Province Based on CE-318 Observations
• Fangfang HUANG, Weiqiang MA, Suichan WANG, Hong ZHANG, Xiaoyi KONG, Pinrui LU, Xudong WANG, Hao LIU, Yidan YAN
• 2024 Vol. 43 (1): 241-253.  DOI:10.7522/j.issn.1000-0534.2023.00030
• Abstract ( ) PDF (6350KB) ( )

• The quantitative analysis of ground-based observations of atmospheric aerosols is a basic way to understand the optical properties of aerosols and the characteristics of atmospheric pollution， which can provide a certain basis for exploring the direction of pollution control.In recent years， there are few studies on the analysis of aerosol optical properties in different regions of Gansu Province using ground-based observations.In order to understand the atmospheric aerosol optical characteristics of different land surfaces in Gansu Province， we obtained the aerosol optical depth （AOD） of four stations in Gansu Province through ASTPwin software based on CE-318 solar photometer observations from April 2018 to September 2020 and calculated the Angstrom wavelength index α.The distribution and variation characteristics of AOD and α in different regions of Gansu Province in different seasons and the relationship between aerosol optical depth and wavelength index were analyzed.The results show that： （1） the changes of AOD in each wavelength band tend to be consistent in all stations during the observation period， and the AOD value decreases with increasing wavelength.The AOD values of Lanzhou and Gaolan Mountain were the highest in winter， followed by spring and autumn， and the lowest in summer.The winter and spring AOD values of Lanzhou exceeded the annual average by 14.98% and 4.68%， respectively， and the winter AOD value of Gaolan Mountain exceeded the annual average by 3.88%.Dunhuang and Minqin both had the highest AOD values in spring， which were 24.49% and 26.30% higher than their respective annual averages.The seasonal distribution of AOD in Dunhuang was： spring > summer > winter > autumn， while Minqin showed a trend of gradually smaller values from spring to winter.（2） The dominant particles in Lanzhou and Gaolan Mountain are coarse modal in spring and summer， while fine particles dominate in autumn and winter.Dunhuang and Minqin atmospheric aerosols are dominated by coarse modal particles all year round.In the winter of 2019， the AOD value of Lanzhou was 68.0% higher than that of Gaolan Mountain； Dunhuang and Minqin had more serious sand and dust aerosol pollution in spring 2019， and the AOD value of Dunhuang exceeded that of Minqin by 42.42%.（3） The frequency distribution of AOD and α at all sites showed a single-peaked curve， with variability in the range of high-frequency distribution of AOD in different seasons， but they were all below 1.0.The distribution of high-frequency range of α was more complex， with the range of α distribution less than 1.0 in spring in Lanzhou， spring and summer in Gaolan Mountain， four seasons in Dunhuang， and spring， summer and autumn in Minqin， while α in summer， autumn and winter in Lanzhou， autumn and winter in Gaolan Mountain， and winter in Minqin was mainly distributed at 1.1 or above.（4） The relationship between AOD and α differs in different seasons， which shows that the size of the dominant particles of aerosol differs in different seasons when the atmosphere is seriously or locally polluted.In spring when the atmosphere is in local or serious pollution and in summer when the atmosphere is in local pollution， the aerosols at the four stations are mainly large particle size， with the contribution of sand and dust aerosols being larger.In summer when the atmosphere is in serious pollution， Gaolan Mountain aerosol is mainly fine mode particles， Lanzhou， Dunhuang and Minqin aerosol is still controlled by coarse mode， but the proportion of pollution caused by small particle size in Lanzhou is higher than the remaining two stations， of which more than 85% belongs to urban industrial - aerosol pollution.In autumn， when the atmosphere is in serious pollution， Lanzhou and Gaolan Mountain are both dominated by fine modal particles， of which urban industrial-aerosols account for a significant increase， while Dunhuang and Minqin are still dominated by coarse modal particles， of which dust aerosols account for a large proportion.In winter， Lanzhou is still dominated by fine modal particles， while the other three stations are dominated by coarse modal particles.In winter， Dunhuang and Minqin are dominated by coarse and fine modal particles， while Gaolan Mountain is dominated by fine modal particles when the atmosphere is locally polluted.The analysis shows that， in general， aerosol pollution in the northern part of Gansu is dominated by sand and dust aerosols， while aerosol pollution in the southern part of Gansu shows alternating coarse-mode and fine-mode particles， which provides some references for the next study of aerosol properties and atmospheric pollution characteristics in different regions of Gansu by combining satellite remote sensing data.

• Simulation Study of Typical Flash Floods based on Radar-Estimated Rainfall and WRF-Hydro Model
• Yingchun HU, Yaodeng CHEN, Yufang GAO, Tao PENG
• 2024 Vol. 43 (1): 254-263.  DOI:10.7522/j.issn.1000-0534.2023.00044
• Abstract ( ) PDF (2764KB) ( )

• Limitations of complex topography and lack of basic meteorological and hydrological information make the hydrological early warning and forecasting technology in small-scale mountainous watersheds weak.Using high-resolution radar observations to drive distributed hydrological models is one of the effective ways to improve the flood forecasting capabilities in small mountainous watersheds.Focusing on the Erhe river basin located in central Chongqing as the study area， a study of WRF-Hydro model flash flood simulation based on radar-estimated rainfall data is carried out to evaluate the hydrological application effect of radar-estimated rainfall and the applicability of WRF-Hydro model in small mountainous watersheds.The typical storm flood process in the watershed was selected， and the WRF-Hydro model was driven by the estimated rainfall data from S-band Doppler weather radar， and further compared with the XAJ model to analyze the simulation effects.The results show that： （1） the WRF-Hydro model driven by radar-estimated rainfall data provides a better simulation of the flood process， flood flow and peak-to-peak time in the Second River Basin， with the Nash efficiency coefficient above 0.65， the Kling-Gupta efficiency coefficient above 0.50 and the correlation coefficient above 0.85.（2） Comparing the WRF-Hydro model with the XAJ model， the simulation effectiveness of the WRF-Hydro model is superior to that of the XAJ model in the Erhe River basin， with a difference of 0.03 in the Nash coefficient and 0.04 in the correlation coefficient， further indicating the superior flood simulation performance of the WRF-Hydro model in small mountainous basins.Overall， the WRF-Hydro model based on radar-estimated rainfall data exhibited satisfactory flood simulation performance in the Erhe basin， and can be further applied in similar small-scale mountainous basins.

• Analysis on Spatio-Temporal Variability of Fractional Vegetation Cover and Influencing Factors from 2000 to 2020 in Southwestern China
• Yuting LIU, Lei WANG, Xiehui LI, Lei GUO
• 2024 Vol. 43 (1): 264-276.  DOI:10.7522/j.issn.1000-0534.2023.00052
• Abstract ( ) PDF (2323KB) ( )

• The southwestern China is a vital ecological safeguard and is characterized by ecological fragility and climate sensitivity.Based on the MOD13A3 NDVI dataset， this study used a pixel dichotomy model to calculate the average Fractional Vegetation Cover （FVC） from 2000 to 2020 annually， during growing seasons， and in each of the four seasons for the whole southwestern China and its provinces， a spatio-temporal variation analysis was then performed on FVC across different time scales.The study also discussed the primary factors influencing FVC changes over the past 21 years， using ERA5 temperature data， GPCP satellite precipitation data， and DEM data.Finally， the Hurst Index was used to predict future FVC trends.（1） The results indicate that from 2000 to 2020， the overall FVC in the eastern part of the southwestern China showed an increasing trend， particularly in Chongqing and Guizhou， while Tibet showed a general decline.（2） Spatially， the FVC generally showed a "higher in the east and lower in the west" trend， with areas where FVC increased accounting for 43.9% of the total area， and areas of decrease accounting for 53.5%.（3） Precipitation promotes FVC， while temperature has varied effects in different regions.（4） Human activity significantly impacts FVC， with promotion， suppression， and no effect zones accounting for 40.4%， 47.6%， and 12.0% of the grid percentage， respectively.（5） Elevation and FVC over different time scales are significantly correlated but both exhibit a pronounced declining trend.FVC increases significantly with slope， but decreases when the slope is greater than 25°.The effect of aspect on FVC in the southwestern China is less significant than that of slope， elevation， and climatic factors.（6） In the future， the FVC in Tibet and the eastern parts of Sichuan， Yunnan， and Guizhou in the southwestern China will increase， while most areas of western Sichuan and the Hengduan Mountains will exhibit a decreasing trend.The results can provide data support and scientific guidance for the formulation of ecological protection plans in the southwestern China.