重庆夏季暴雨和非暴雨天气的西南低涡个例对比分析

Comparative Analysis of Heavy Rain and Non-Heavy Rain Cases Associated with Southwest Vortexes in Summer in Chongqing

针对带来重庆暴雨和未带来暴雨的的两类西南低涡,使用重庆34个常规地面站降水资料和NCEP分析资料,采用天气动力学诊断方法,开展个例对比分析。结果表明:能给重庆带来暴雨的西南低涡表现为一个深厚系统;500 h Pa重庆上空为一深槽,200 h Pa上处于高空急流入口区右侧,有明显的辐散,重庆南北两侧形成两个闭合的次级环流圈,非常有利上升运动维持;700 h Pa上来自河西走廊的偏西气流和印度洋的暖湿气流相遇,在重庆上空形成一个暖舌,IPV分析发现到达重庆的冷空气较弱;四边水汽收支诊断表明,东、南以及西边界是水汽输入边界,只有北边界是水汽输出边界,使得重庆上空水汽出现盈余,利于暴雨发生。而不能给重庆带来暴雨的西南低涡表现为对流层中层的浅薄涡旋;500 h Pa重庆处于脊前西北气流控制下,200 h Pa无明显辐散,重庆上空表现为弱的下沉运动,两侧无明显的闭合次级环流圈;700 h Pa上形成一个气旋性环流,重庆上空很少有来自海洋的暖湿气流,IPV分析显示影响重庆的冷空气较强;四边水汽收支诊断表明,西边界和北边界是水汽输入边界,而南边界和东边界是水汽输出边界,使得重庆上空水汽表现为亏损,不满足暴雨发生的水汽条件。

Based on the observed precipitation data from 34 conventional surface weather stations of Chongqing and NECP analysis data,we contrastively analyzed two cases associated with Southwest Vortex（ SWV） over Chongqing using dynamic diagnostic method. The results show： SWV which can bring heavy rain is a deep system,and there is a deep trough over Chongqing at 500 h Pa,and exists obvious divergent zone at 200 h Pa at the right side of the upper-level jet entrance region. Two closed secondary circulations are formed in both south and north sides of Chongqing,which are beneficial to the maintenance of updraft in Chongqing area. At 700 h Pa,westerly airflow from Hexi Corridor meets with the warm and moisture airflow from the Indian Ocean,and forms a warm tongue over Chongqing.Isentropic Potential Vorticity（ IPV） analysis finds the cold air is weak. Moisture budget of four sides shows that western,southern and eastern boundaries are water vapor input boundaries except for the northern boundary,which results the convergence of water vapor over Chongqing and contributes to the heavy rain. Meanwhile,SWV which cannot bring heavy rain in Chongqing is a shallow vortex in middle troposphere,and the northwest airflow before the ridge at 500 h Pa dominates Chongqing area.There is no obvious divergent movements at 200 h Pa,and there are not closed secondary circulations. Warm and moist air come from marine cannot reach Chongqing where is occupied by obvious cold air. Moisture budget from four sides shows that southern and eastern boundaries are water vapor input boundaries,while the southern and eastern boundaries are output,which resulted in the negative vapor supply over Chongqing and did not meet the water vapor condition of heavy rain.