一次东北冷涡衰退阶段暴雨成因分析

东北冷涡暴雨一般发生在冷涡发展阶段, 冷涡衰退阶段发生暴雨的几率不高, 在日常业务预报中往往容易忽视冷涡衰退阶段暴雨的预报, 容易出现漏报的现象。作者结合观测资料和数值模拟结果, 对2005年6月21日发生在吉林省中东部地区的一次暴雨过程进行分析。结果表明: 这次暴雨发生在东北冷涡衰退阶段, 强降水区处于非常弱的对流不稳定区, 低空不同层次上急流的耦合与脉动, 在时间和空间上形成“接力” 之势, 给雨区带来特定的水汽配置并在雨区上空形成合适的不稳定环境, 导致雨区上空湿位涡的强烈增长, 在弱对流不稳定和条件对称不稳定的共同作用下, 层状云中形成对流并发展, 产生了暴雨天气。重力惯性波是暴雨产生的可能触发机制。

Analyses of Formation Mechanisms of a Rainstorm during the Declining Phase of a Northeast Cold Vortex

The rainstorm usually occurs in the developing stage of northeast cold vortex,not in the declining phase.So people are apt to miss the rainstorm that appears during the declining phase of cold vortex.Based on the observed data and the numerical simulation results,the process of the rainstorm which occurs during the declining phase of one northeast cold vortex is analyzed in middle and eastern Jilin Province on 21 Jun 2005.The results show that there is one instable layer at the center of the rainstorm,with a little convective available potential energy(CAPE).The coupling and fluctuation of low levels jet in different layers present the "relay shape" in time and space,which leads to the especial water-vapor configuration and the right instability condition,which further lead to the intense development of moist potential vorticity in the heavy rain area.Under the condition of convective instability(CI) and conditional symmetric instability(CSI),the mesoscale convective system(MCS) forms and the convection develops in the stratiformis cloud,which directly bring the precipitation.Gravity wave is the possible trigger mechanism of rainstorm.