桂林“5·22”大暴雨的MCS特征及对短时强降雨的影响

Characteristics of mesoscale convective system in Guilin during the "5·22" rainstorm process and its effects on short-time heavy rainfall

利用常规观测资料、风云气象卫星四号A星(FY4A)资料、欧洲中期天气预报中心全球第五代大气再分析数据集(EAR5)以及桂林和柳州多普勒雷达资料,分析2023年5月22日桂林极端大暴雨过程的中尺度对流系统(MCS)特征及其对短时强降雨的影响。结果表明,此次过程降水时段集中、局地性强、极端性大,强降水时段与对流云团的强烈组织发展阶段基本一致。在“北槽南涡”的环流背景下,高原低涡东移及其切变线诱发MCS生成,地面冷空气和辐合线使其强烈发展。降水回波强度强,质心低,降水效率高,强回波柱在桂林市区维持。MCS具有低层正涡度、负散度,高层负涡度、正散度的垂直结构,上升速度大,利于发展维持。MCS发展前期对流有效位能(CAPE)值迅速增大,桂林处于有利的抬升环境中,大气可降水量峰值出现时间与强降水发生时间对应。

Using conventional observation data,FY4A satellite data,EAR5 reanalysis data,data from Doppler radar in Guilin and Liuzhou the characteristics of mesoscale convective system(MCS) during the extreme heavy rainstorm in Guilin on May 22,2023,and its effects on short-term extremely heavy precipitation are analyzed.The results show that:The precipitation period of this process is concentrated,highly localized,and extreme.The period of heavy precipitation is basically consistent with the stage of strong organization and development of convective clouds.Under the circulation background of the "northern trough and south vortex",the eastward movement of the plateau vortex and its shear line induce the generation of MCS,which is strongly developed by surface cold air and convergence lines.The precipitation echo intensity is strong,the centroid is low,and the precipitation efficiency is high.The strong echo column is maintained in the urban area of Guilin.MCS has a vertical structure with positive vorticity and negative divergence in the lower levels,and negative vorticity and positive divergence in the upper levels,with a large upward velocity,which is conducive to the development and maintenance of MCS.In the early stage of MCS development,the CAPE value increases rapidly,and Guilin is in a favorable uplift environment.The occurrence time of peak atmospheric precipitation corresponds to the occurrence time of heavy precipitation.