影响云南的西南低涡统计特征

利用1980—2008年逐日08:00(北京时,下同)和20:00 700hPa高空图和云南125个测站的逐日降水量资料,对影响云南的西南低涡移动路径、时间变化、维持时间和对应的降水特征进行了统计分析。结果表明,约1/8～1/7的西南低涡能够移出四川并影响到云南,但过去30年来其总趋势是减少的。影响云南的西南低涡初生涡源区主要集中在九龙和四川盆地,东南路径最多,西南和偏南路径次之,受地形影响西南低涡一般影响不到滇西边缘和滇西南地区。春末和夏季西南低涡移出影响云南的频数最多,秋末和冬季最少。西南低涡开始影响云南的时间表现出日变化特征,在白天的影响几率为61.54%,其生命史呈指数衰减,大多不超过1天。西南低涡移出源地后,约有13.5%的低涡会影响云南并出现全省性强降水过程。其中,偏南路径西南低涡造成的强降水主要分布在哀牢山以西地区,东南路径的主要暴雨中心位于滇中和滇东南,西南路径的强降水主要分布在滇东地区。西南路径大到暴雨的出现频率最高、强度最强,应引起足够的重视;东南路径虽然最多,但大到暴雨的出现频率和强度均低于平均值。

Statistical Characteristic of Southwest Vortex Influencing Yunnan Region

Based on the data of the 700 hPa synoptic map at 08:00 and 20:00 from 1980 to 2008,the characteristics of moving track,annual,monthly and daily variations,maintenance time,corresponding precipitation caused by southwest vortex were statistically analyzed.The results show that nearly one eighth or one seventh of southwest vortexes can move out of Sichuan Province affect Yunnan,and its linear trend in past 30 years is decreased.Their vortex source regions are mainly near Jiulong and Sichuan Basin.The occurrence frequency of southeast ward path is the highest,then the southwest-and south-ward paths.Generally,under the topographical influence,southwest vortexes could not influence on the edge of western and southwest Yunnan.In the late spring and summer,the movement of southwest vortex affects Yunnan with the highest frequency,while the frequency is the least in the late autumn and winter.The probability of southwest vortex influencing Yunnan is about 61.54% at 08:00.Their life periods are exponential decay,mostly no more than one day.Nearly 13.5% of southwest vortex cause heavy precipitation process in Yunnan.The heavy precipitation caused in south path occurs mainly in western Ailao Mountains.the heavy precipitation caused southeast path mostly occurs in the central and southeastern Yunnan,and one caused southwest path mostly occurs in the east of Yunnan.Among of them,the frequency and intensity of occurring heavy precipitation are the highest in southwest path,and which should be paid more attention.Although the most of southwest vortexes can move out to influence Yunnan along the side of southeast path,the frequency and intensity of occurring heavy precipitation were below the mean.