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

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 500 hPa 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.