贵港市“5.20”下击暴流过程超级单体结构演变与环境特征分析

Analysis of supercell structure evolution and environmental characteristics of downburst in Guigang City of Guangxi On May 20, 2020

2020年5月20日受强对流系统影响广西贵港市出现下击暴流,造成严重损失。本文利用常规气象观测资料、多普勒雷达资料、NCEP再分析资料,对该下击暴流超级单体的结构演变与环境特征进行了分析。结果表明:(1) 2020年5月20日贵港市黄练镇厂房损毁和人员伤亡是小尺度下击暴流造成的辐散性阵风所致。(2)造成下击暴流的超级单体初生阶段向东北方向移动,增强、成熟和消亡阶段向东南方向移动;该单体成熟阶段具有钩状回波、回波悬垂、有界弱回波区、中气旋、中层径向辐合等特征且维持了较长时间。(3)该过程500 hPa广西有短波槽东移,槽后干冷的西北气流与低层西南暖湿空气在广西中南部造成强垂直风切变和不稳定层结,一方面使风暴体倾斜增强了中层干冷气流的侵入,另一方面加大了由水凝物粒子蒸发冷却作用引起的负浮力。(4)中低层暖平流强迫和地面辐合线是此次下击暴流的主要的强迫和触发机制;初始对流在桂西南触发,分散的对流单体在宾阳与贵港附近加强为高度组织化的对流系统,中层干冷空气的侵入、高的低层环境相对湿度与凝结物的重力拖曳共同作用产生强的下沉气流和近地面灾害性大风。

Based on the conventional meteorological observation data, Doppler radar data and NCEP reanalysis data, we have conducted an analysis of the structural evolution and environmental characteristics of the downburst in Guigang on 20 May 2020,which was affected by the strong convection system, causing serious losses. The results are as follows.(1) The damage of the factory building and casualties in Huanglian town of Guigang City on 20 May 2020 are caused by the divergent gust associated with the small-scale downburst.(2) The supermonomer which caused the downburst flow moves to northeast in its primary stage, and to southeast in its the strengthening, mature and dying stages.The mature stage of the monomer has the characteristics of hook echo, echo suspension, bounded weak echo region, medium cyclone and middle radial convergence. It has been maintained for a long time.(3) During this process, there is a short wave trough moving eastward at 500hPa in Guangxi. The dry and cold northwest air located above the low-level southwest warm and wet air causing strong vertical wind shear and unstable stratification in central and southern Guangxi. On the one hand, it tilts the storm inclined and enhances the invasion of the middle dry and cold air. On the other hand, it increases the negative buoyancy due to evaporative cooling of condensate particles.(4) The low-level warm advection forcing and ground convergence line are the main forcing and triggering mechanisms of the downburst. The initial convection is triggered in southwest Guangxi, and the scattered convective cells are strengthened into a highly organized convective system near Binyang and Guigang. The intrusion of middle-level dry and cold air, high low-level environmental relative humidity and the gravitational drag of condensate jointly produce strong downdraft and near surface disastrous gale.