大气运动非平衡强迫与“98·7”突发性特大暴雨诊断分析

Diagnostic Analysis of Unbalanced Force of Atmospheric Motion and an Abrupt Heavy Rain during July 1998

应用常规气象和卫星资料 ,对 1 998年 7月 2 1日发生在武汉附近地区的突发性特大暴雨过程进行了分析 ,结果显示 :( 1 )引发本次突发性特大暴雨的系统是一个中 β尺度对流云团。 ( 2 )该中 β尺度暴雨系统在对流层高低层没有独立的负、正涡度大值中心区与之对应 ,辐合层并不十分深厚 (低于 50 0hPa) ,且气流散合强度 ( 1 0 - 4s- 1)较旋转强度 ( 1 0 - 5s- 1)大一个量级 (D >>ζ)。 ( 3)在暴雨发生前 1 0余小时 ,大气运动已处于较强的非平衡状态 ,且越临近暴雨发生 ,U <0的非平衡性越强 ;而在暴雨达到强盛期后 ,大气运动即由U <0的非平衡态转为U >0的非平衡态。 ( 4 )对流层低层大气运动非平衡动力强迫与 2 0 0hPa等压面上的中 β尺度强辐散是本例暴雨和中

An abrupt heavy rain event occurred in Wuhan from 20 to 22 July 1998 is analyzed by using conventional and satellite data. The results show that: (1) The event was caused by a meso β scale convective cloud cluster. (2) The meso β scale system is not related with strong cyclone vorticity or ant cyclone vorticity center in lower or upper troposphere. The divergence strength of the system is higher 10 1s -1 than that of vorticity. (3) 10 hours before its occurrence, the atmospheric motion was already unbalanced. After the precipitation, its intensity got strongest and it changed into U >0 from U <0. (4) The unbalanced force of lower atmospheric motion and strong divergence in the upper atmosphere are led to the initiation and development of the meso-βscale system as well as the occurrence of heavy rain.