云南省区域性短时强降水时空分布及其分类天气系统特征

Spatial and temporal distribution of regional short-term heavy precipitation events in Yunnan Province and classification of weather system characteristics

摘要:

山地复杂地形地貌叠加特殊的地理位置使得短时强降水成为云南省发生频率较高的一种强对流天气,常引发自然灾害。基于中国气象局陆面数据同化系统(CMA Land Data Assimilation System,CLDAS)产品提供的2008—2022年0.062 5°×0.062 5°高空间分辨率的逐小时降水和ERA5逐小时再分析资料,本研究使用K均值聚类法对91次区域性短时强降水天气过程的环流进行聚类分型,并揭示其三维天气系统配置及热、动力特征。结果表明:1)短时强降水以滇东南发生频率最高,滇东南、滇西南和滇西的部分地区强度最强。日内以20—21时(世界时)强度大,14—15时频次多。年内以7月降水强度最大,6月降水量最多。同时,年际变化明显,其中极强值年份降水量可达80 mm以上,其多年平均降水量维持在26 mm左右。2)区域短时强降水天气过程可分为西风小槽型、高空长槽型和副高外围型,以高空长槽型发生频次最多、强降水范围最大。3)3类天气系统配置都存在有利于短时强降水发生的动力、水汽和热力条件:200 hPa存在强辐散区(如高空急流南侧),500 hPa位于槽前或副高西侧并伴有上升运动,中低层配合有低层切变线和低涡、地面辐合线等;同时,水汽多来自孟加拉湾,水汽随偏西气流至云南上空后辐合,K指数大于38℃。高空长槽型由于中低层切变线和低涡更靠近云南中部,低空锋面及冷空气活动更强,云南区域上空低(高)层辐合(散)最强,且由于其前倾的垂直结构引起的热力不稳定也最强,导致区域上空整层的上升运动和水汽辐合最显著、范围最大,故由其引起的短时强降水范围更大。

Abstract:

The complex topography and unique geographical location of Yunnan Province contribute to the frequent occurrence of short-term heavy precipitation,a severe convective weather phenomenon often associated with natural disasters.Using hourly precipitation data at a high spatial resolution of 0.062 5°×0.062 5° from the China Meteorological Administration Land Data Assimilation System (CLDAS) and ERA5 hourly reanalysis data from 2008 to 2022,this study analyzes 91 regional short-term heavy precipitation events and classifies them using K-means clustering.The three-dimensional weather system configuration and its thermal and dynamic characteristics are also examined.The results reveal the following:1) Short-term heavy precipitation is most frequent in southeastern Yunnan,with the highest intensity observed in southeastern,southwestern,and western region of the province.Peak intensity occurs between 2000 UTC and 2100 UTC,while peak frequency is observed from 1400 UTC to 1500 UTC.Inter-annual variability is significant,with extreme years experiencing precipitation exceeding 80 mm,compared to an average of 26 mm.2) The precipitation events can be categorized into three types:the westerly-small trough type,the upper-level long trough type,and the peripheral type of the subtropical high.The upper-level long trough type exhibits the highest intensity and frequency,occurring across the entire province.3) Favorable conditions for precipitation include dynamic,thermal,and moisture-related factors.At 200 hPa,strong divergence is observed in regions such as the southern side of the upper-level jet stream,located in front of a trough or on the western side of the subtropical high,coupled with upward motion at 500 hPa.This is combined with low-level shear lines,low vortices,and surface convergence zones in the middle and lower troposphere.Moisture convergence primarily originates from the Bay of Bengal,interacting with westerly airflow over Yunnan Province.The K-index exceeds 38 ℃ in these events.Among the three types,the upper-level long trough type features the strongest low-level fronts,cold air activity,and mid-and low-level shear lines and vortices centered over Yunnan.Its forward-tilting vertical structure creates strong thermal instability,resulting in enhanced upward motion,significant water vapor convergence across atmospheric layers,and the heaviest precipitation.