2020年8月黄河下游大暴雨过程中尺度特征分析

Analysis of the Mesoscale Characteristics of Heavy Rainstorm Process in the Lower Yellow River in August 2020

利用常规观测资料、区域自动站分钟和小时资料、NCEP(美国国家环境预报中心)1°×1°再分析资料及卫星云图资料等,对2020年8月3—4日黄河下游一次大暴雨过程的大尺度环流背景、环境场、触发机制和中尺度系统等进行分析。结果表明:台风登陆、副热带高压边缘暖湿气流加强和冷空气影响是产生大暴雨的有利环境场;β中尺度对流系统(MβCS)的形成和维持是造成强降雨的直接原因;强降雨第一阶段上升运动中心在中高层,是由云体范围大而孤立的MβCS造成的,地面辐合线、低层冷空气提供了触发机制,水汽主要来源于副热带高压边缘和东南沿海;第二阶段上升运动中心在中低层,径向垂直环流的形成使上升运动持续发展,强降雨是由多个对流云团合并而成的MβCS造成的,TBB(云顶亮温)梯度大,地面辐合线、风切变提供了触发机制,水汽主要来源于东南沿海。

The large-scale circulation background, ambient field, triggering mechanism and mesoscale system of a severe torrential rainfall process with localized extremely severe rainstorm which occurred in the lower Yellow River during 3-4 August 2020 were analyzed in this paper based on the conventional observation data, minutely and hourly data of regional automatic stations, NCEP(U.S. National Environmental Forecast Center) 1°×1° reanalysis data and satellite cloud images. The results show that the typhoon landing, the strengthening of warm-humid airflow at the edge of the subtropical high and the influence of cold air are composed of the favorable ambient fields for producing heavy rainstorm. The formation and maintenance of β mesoscale convective system(MβCS) is the direct cause of the severe rainfall. In the first stage of the severe rainfall, the updraft center is in the middle and upper levels, which is caused by the large and isolated MβCS of clouds. The ground convergence line and low-level cold air provides the trigger mechanism, and the water vapor mainly comes from the edge of the subtropical high and the southeast coastal area of China. In the second stage, the ascending movement center is in the middle and low levels. The formation of radial vertical circulation makes the ascending movement develop continuously. The heavy rainfall is caused by the MβCS formed by the merger of multiple convective cloud clusters. The gradient of TBB(Genting quite black body brightness temperature) is large, the ground convergence line and wind shear provides the trigger mechanism, and the water vapor mainly comes from the southeast coast.