Analyses of Formation Mechanisms of a Rainstorm during the Declining Phase of a Northeast Cold Vortex
一次东北冷涡衰退阶段暴雨成因分析

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.