北京一次暴雨过程的成因分析

2011年6月23日下午到夜间,受蒙古低涡东移南下天气过程及冷暖空气共同作用影响下,北京地区出现了强雷雨天气过程,局部地区降雨量达到大暴雨标准。此次大暴雨过程具有突发性、局地性、短时性和高雨强等特点。利用常规天气资料、fnl再分析6 h资料等,对此次大暴雨过程进行了分析,并对其成因作了初步讨论。结果表明:东移南下的蒙古低涡及北京北部、贝加尔湖以东的外蒙古境内的阻塞高压为此次天气过程的影响系统,北京地区处于低槽前部的不稳定区。由垂直速度场可以看出,北京地区处于垂直速度大值中心,同时位温随高度增加而减小的分布状况,表明暴雨发生时北京地区大气层结是极不稳定的,地面低压辐合带配合高空东移的横槽造成高低空辐散带叠加,产生了极强的上升运动,有利于大暴雨的发生发展。近地面东南风将渤海的水汽源源不断地输送到北京地区,借助强的上升运动,在高空呈现很强的水汽通量辐合,为大暴雨的发生提供了充足的水汽条件。

Formation Analysis of a Rainstorm in Beijing in 20 1 1

From afternoon to night of June 23,2011,the strong thunderstorm weather process occurred in Beijing due to the Mongolia vortex moving eastward and southward and the effect of cold and warm air,and during the storm weather process,localized rainfall reached the standard of heavy rainstorm.This rainstorm weather had some characteristics including the suddenness,local,short-term and high rainfall intensity.Based on conventional weather information and the FNL analysis data of six hours,the storm weather process was analyzed and a preliminary discussion about its formation causes was made in this paper.The results show that the Mongo-lia vortex moving eastward and southward and the blocking high over Mongolia resulted in this weather process,Beijing happened to be at the unstable region in front of the trough.From the analysis of vertical velocity,Beijing was located in the center of maximum verti-cal velocity,and the potential temperature decreased with height increase,which indicated that the atmospheric stratification was ex-tremely instable over this region when heavy rainfall occurred.Ground pressure convergence zone cooperated with the transverse trough moving eastward over the up level resulted in divergence zone overlapping,which produced the strong ascending motion,and it was conducive to the development of rainstorm.The southeast wind near the ground transported vapor from Bohai to the Beijing area,and with the strong ascending motion,the strong convergence of moisture flux occurred at up level,which provided adequate moisture con-ditions for the rainstorm.