一次西南涡影响云南强降水过程分析

通过对2004年8月4日西南涡影响下云南强降水过程的环流背景、卫星云图演变以及动力、热力条件的分析,发现这次西南涡是一个具有斜压性的极其深厚的系统,随高度前倾,高层500 hPa上的西南涡表现尤为明显,并且诱发了低层700 hPa西南涡的产生,强降水主要出现在西南涡的西南方;强降水与强上升运动区和正涡度区有很好的对应关系,并且正涡度和上升运动的出现比气旋性环流场有24 h的提前时间,对于强降水预报更具有预示性,它们是一个逐渐由高层向低层发展的过程;中-β尺度对流云团在金沙江河谷南移合并加强,形成了中-α尺度涡旋状云系,其中的对流云团在强降水中作用较大;强降水正是出现在对流层低层(MPV1 MPV2)的负值范围内,这也说明西南涡涡旋云系的发展与正压和斜压不稳定都有关系,对流层低层MPV1<0和MPV2<0有利于暴雨的发生。

ANALYSIS OF A HEAVY PRECIPITATION AROUSED BY SOUTHWEST VORTEX IN YUNNAN

By analysing circulation background,satellite cloud picture evolution and dynamical,thermodynamical conditions of the heavy precipitation aroused by the southwest vortex in Yunnan on August 4,2004.The results show that the southwest vortex is very deep and baroclinic system,the southwest vortex on 500hPa is more obvious and arouses the southwest vortex on 700 hPa,the heavy precipitation is to the southwest of the southwest vortex,the heavy precipitation field has a good relation to the strong ascending motion and the positive vorticity that have stronger indication than the cyclonic circulation for the heavy precipitation and they gradually develop from the high altitude to the low altitude,mesoscale convective cloud clusters move to the south and develop into the mesoscale vortex cloud system arousing the heavy precipitation in Yunnan,the heavy precipitation is in the negative field of(MPV1 MPV2),both of barotropic and baroclinic instability are related to the enforcement of vortex cloud system,MPV1<0 and MPV2<0 are favorable to the heavy precipitation.