一次区域暴雨过程综合诊断分析

Comprehensive Diagnostic Analysis of a Regional Heavy Rainfall

利用NCEP 1°×1°的6 h再分析资料对2008年7月22日河南省南阳市的区域性暴雨天气进行了综合诊断分析,结果表明:此次暴雨过程是中低层的西南涡在高空急流的引导下,沿着河套高压与副高之间的辐合带移出造成的。降雨的水汽供应主要来自对流层中低层,且水汽强辐合出现在强降雨前。随着对流活动的发展,水汽通量和水汽辐合都向高层发展,湿层明显增厚。在整个降雨过程中,700 hPa垂直螺旋度正值中心的位置和强度与西南涡的移动和强弱变化有很好的对应关系,垂直螺旋度正值长轴区与切变线辐合区相吻合,在某种程度上能反映出西南涡的移动和强度的演变;垂直螺旋度强弱的变化与暴雨强度变化基本一致。高层辐散、低层辐合的大气垂直结构能增强大气的抽吸作用,促进垂直上升运动的发展,反之,抑制垂直上升运动,降雨减弱。上、下层负、正垂直螺旋度耦合的结构对暴雨的发生和维持非常有利。在雷达速度PPI上,逆风区的出现预示着局地强降雨的产生。

This article makes a comprehensively diagnostic analysis of a regional rainstorm on July 22 in 2008 in Nanyang of Henan province based on NCEP 6 h reanalysis data with resolution 1°× 1°. The results show that the cause of the formation of the rainstorm is under the guidance of upper jet, the southwest vortex in the middle and low-level emigrate along with the convergence zone between Hetao high- pressure and subtropical high pressure. The water vapor supply of the rainfall mainly comes from the mid- dle and low-level of the troposphere and the water vapor strong convergence appears before the strong rainfall. With the development of convective activity, the water vapor flux and water vapor convergence develop toward high-level and the wet layer obviously thickens. During the entire rainfall process, the lo- cation and intensity of 700 hPa positive vertical helicity center have a very good corresponding relation- ships with the movement and the strong-weak change of southwest vortex, and the long axis district of the positive vertical helieity coincides with the shear line convergence area, it can reflect the evolution of the movement and intensity of the southwest vortex in a way. Changes in the intensity of vertical helicity are in the basic agreement with the changes in the strength of heavy rainfall. Atmospheric vertical structure of the high-level divergence and low-level convergence can strengthen the ＂pumping effect＂ and promote the development of vertical movement. Otherwise, it can suppress the vertical ascent movement, and the rainfall will weaken. The coupling structure of the vertical helicity that the high is negative and the lower is positive is very favorable to the development of weather system and the occurrence and maintenance of heavy rainfall. On radar radial velocity PPI, ＂adverse wind regions＂ leads to local heavy rainfall.