华南前汛期冷空气影响下两次飑线大风过程的对比分析

Comparison and Analysis of Two Squalls Under the Effect of Cold Air Activity During Annually First Rainy Seasons of Southern China

利用常规气象资料、自动站资料、FNL1°×1°再分析资料和多普勒雷达资料对比分析了2017年在西风槽前并伴随着冷锋影响下的两次飑线大风过程,其中“4·21”较“5·8”过程造成了更严重的灾害性大风。结果表明:(1)高空槽和地面冷锋的配置提供了深厚的动力条件,但中层槽靠近后增强的垂直风切变是大风产生的关键原因,垂直风切变的大值区对大风落区具有指示意义。(2)华南地区夏半年,探空曲线对于6h后的指示意义不大,CAPE及假相当位温随高度减小虽能表征层结不稳定度,但对地面大风的指示意义不强。(3)倾斜的结构有利于“4·21”对流的发展,强回波质心高是“4·21”产生地面大风的主要原因,“5·8”过程没形成倾斜结构的同时低层的上升运动更为强烈,削弱了雨滴下降对空气的拖曳作用,不利于地面大风的产生。

Using conventional meteorological observations,data from automatic weather stations,FNL 1°×1°reanalysis and Doppler data,this paper compares and analyzes two squalls that took place in April 21 and May 8,2017 ahead of a westerly trough and under the effect of a cold front.Destructive high wind caused by the former process were more serious than that by the second.The result is shown as follows.(1)The allocation of an upper-level trough and a surface cold front provided deep dynamic conditions while the key reason for the generation of high wind was a shear of vertical wind that strengthened after a mid-level trough arrived.The zone of large vertical wind shear indicated where the high wind could occur.(2)For the summer half of the year in southern China,sounding curves were not useful for the forecasting 6 hours a-head,and the decreases of CAPE and pseudo-equivalent temperature with height were descriptive for strati-form instability but less indicative for surface high wind.(3)During the April 21 process,a declining struc-ture was favorable for the development of convection and a high-level mass core of intense echo was responsi-ble for the surface high wind.In contrast,there was not any declining structure with the May 8 process but ascending motion was more intense at the low level that weakened the drag effect of falling raindrops on the air,unfavorable for the generation of surface wind.