桂林“5.22”极端强降雨过程的观测分析

Observation analysis of"5.22"extreme rainfall event in Guilin

2023年5月22日凌晨至上午,桂林市区北部发生极端强降雨,1 h和3 h雨量均突破当地历史记录,导致严重城市内涝。利用常规观测、地面加密自动站、多普勒天气雷达以及ERA5再分析等资料对此次强降雨过程进行分析。结果表明:(1)过程发生在副热带高压边缘,受低层切变线和地面冷锋南下影响,持续增强的西南急流为极端强降雨提供充足的水汽和能量;(2)强降雨回波由线状对流演变,线状对流与地面冷空气适时相遇,移向和形态发生改变,同时其西侧不断发展的新生单体加入形成“列车效应”,导致极端降雨产生,且降雨回波呈现低质心高效率的特征;(3)弱冷空气适时入侵,增强对流降雨并加强冷池出流,在其前沿的暖湿区域中触发新生对流,有利于强降雨的发展和持续;(4)对流单体在东移过程中通过云桥合并和云体扩大发展两种方式合并形成新的云团,并迅速发展,使降雨增强,对流单体之间的相互作用和合并是强降雨持续和加强的主要机制;(5)国内多家业务模式均低估此次过程雨强,预报降雨中心存在偏差,主要原因是模式预报地面冷空气影响时间出现偏差。

An extreme heavy rainfall event struck the northern part of the Guilin urban area in the early morning of May 22,2023,breaking local historical records for both hourly and three-hourly precipitation,resulting in severe urban waterlogging.Analysis was conducted using data from routine observation,ground-based dense automatic stations,Doppler weather radar,and ERA5 reanalysis.The results are as follows.(1)This event occurred on the edge of the subtropical high-pressure system,with the continuous strengthening of the southwest jet stream providing abundant moisture and energy for the extreme rainfall under the influence of the low-level shear line and the southward movement of the surface cold front.(2)The echoes of heavy rainfall evolved into a linear convection,which changed the direction and shape when timely met with the surface cold air.Meanwhile,the continuously developing new individual cells on its western side joined to form a"train effect,"leading to extreme rainfall.The echo exhibited characteristics of low core and high efficiency.(3)The timely intrusion of weak cold air intensified convective rainfall and enhanced cold pool outflow,triggering new convection in the warm and moist region ahead of it,which favored the development and persistence of heavy rainfall.(4)During the eastward movement of individual convective cells,they merged through cloud bridges and expanded through cloud development,forming new cloud clusters and rapidly intensifying precipitation.The interaction and merging of convective cells were the main mechanisms for the prolonged and intensified heavy rainfall.(5)Various numerical models underestimated the intensity of this event,with biases in forecasting the rainfall center mainly due to deviations in the timing of forecasting the influence of surface cold air.