1979—2016年夏季西南涡活动及其与降水的关系

Analysis of the Southwest Vortex activities in summer and their relationship with precipitation during the period of 1979—2016

利用1979—2016年ERA-Interim一日四次高度场、风场再分析资料,根据源地的不同将西南涡细分为九龙涡、盆地涡和小金涡,对1979—2016年夏季(6—8月)不同涡源的西南涡的活动规律及其降水特征进行统计分析。结果表明,夏季西南涡平均年发生频数为11.6 a^(-1),其中生成的盆地涡最多(9.3 a^(-1)),九龙涡次之(1.9 a^(-1)),小金涡最少(0.4 a^(-1))。就移动频率而言,盆地涡移出率最高(44.2%),其次为小金涡(30.8%),九龙涡最低(29.73%)。38 a中夏季高影响型西南涡共有140例,只有105例能移出源地。生命史超过36 h的高影响型西南涡都会带来降水,并且超过88%的概率会造成大雨及以上的降水。高影响型九龙涡和盆地涡产生大雨及以上天气的概率分别是83%、91%,远远高于小金涡。

The Southwest Vortex is one of the most powerful rainstorm systems in China,and requires greater attention from scholars,due to the fact that the previous investigations on the Southwest Vortex have not formulated its occurrence and development from different origins.In this study,the ERA-INTERIM reanalysis data with 2.5°×2.5°resolution of the geopotential height and wind with 6-hour resolution from June to August during the period of 1979-2016 were presented.According to the different origins,the southwest vortexes(SWVs)present were subdivided into Jiulong area vortexes,Sichuan Basin vortexes and Xiaojin area vortexes.The characteristics of the SWVs were statistically analyzed after defining the closed cyclone circulation and setting up the statistic method of the vortex movement routine according to wind field.Next,the climate characteristics in the SWVs anomaly years,along with the characteristics of precipitation contributed by the SWVs from 1979-2016 in summer(June to August),were quantified and analyzed emphatically.The results suggest that the annual frequency of occurrence of SWVs was 11.6 a-1,and the maximum number of vortexes generated in the Sichuan Basin(9.3 a-1),followed by the Jiulong area(1.9 a-1),at least in the Xiaojin area(0.4 a-1).As for moving rate,the Sichuan Basin vortexes reached 44.2%(the maximum),followed by 30.8%for the Xiaojin vortexes,with the Jiulong vortexes being the slowest at 29.73%.There were a total of 140 high-impact SWVs generating during the summers of the 38 years,while only 105 cases moved out of the places of origin(among them 84 Sichuan Basin,17 Jiulong and 4 Xiaojin area vortexes).The migratory paths of the high-impact Sichuan Basin and Jiulong vortexes were respectively based on eastward and northeastward-migrating paths.In order to research the relationship between migratory SWVs and precipitation,we drew a distribution map of the rain belt and strong precipitation center,and concluded that the high-impact SWVs persisting for more than 36 hours would lead to precipitation,while probability of over 88%would lead to heavy rainfall and the above precipitation.The longer the lifespan of the SWVs was,the more likely it was that the rainstorm process would be brought to the downstream area.The respective probabilities of causing heavy rainfall and the above precipitation for the high-impact Jiulong and Sichuan Basin vortexes were 83%and 91%,which had significantly higher ratios than the Xiaojin area vortexes.At the same time,the rain belt caused by the SWVs was consistent with their migratory path.The results of this study also show that,when the high-impact Sichuan Basin vortexes moved northeastward,the rain belt appeared in the areas of Hubei,Anhui and Shandong,while some also appeared in the northeast area.The heavy rainfall centers were mainly distributed at the junction of Hubei and Anhui.When the high-impact Sichuan Basin vortexes moved out along the eastward path,the heavy rainfall center was concentrated in the middle and lower reaches of the Yangtze River,where the highest occurrence frequency was found.When the high-impact Sichuan Basin vortexes moved out along the southeast path,there were two main rain belts corresponding to it,one in the Hunan,Jiangxi and Fujian area,and the other in Guizhou and Guangxi,with the latter belt appearing more frequently.The heavy rainfall center mainly occurred at the junction of Guizhou and Guangxi.