2020年7月5—8日长江中下游连续大暴雨特征分析

Characteristics Analysis of Continuous Heavy Rains in the Middle and Lower Reaches of the Yangtse River from July 5 to 8 in 2020

利用地面加密降水资料、NCEP fnl再分析资料和风云4A卫星T_(BB)资料,对2020年7月5—8日长江中下游地区的连续性大暴雨过程进行诊断分析。结果表明,这次连续性大暴雨过程是在有利的大尺度环流背景下,受切变线影响由列车型对流云团产生的。7月5—8日,亚洲中高纬度大气环流调整,贝加尔湖的东阻高崩溃,带动中高纬度的中高层冷空气持续南下,在长江流域与北上的暖湿气流交汇,使得锋区维持,有利于暴雨产生和发展。暴雨期间,低空西南急流的增强提供了有利的水汽输送条件,高空急流增强并发生“倾斜”,高低空急流的耦合在长江中下游上空形成了强烈的高空辐合与低空辐散,使得旺盛的上升运动延伸至对流层高层。在有利的环流背景条件下,中尺度对流系统的“列车效应”是导致本次大暴雨的直接原因。

From July 5 to 8,2020,continuous heavy rains occurred in the middle and lower reaches of the Yangtze River.This paper uses ground-encrypted precipitation data,NCEP fnl reanalysis data and Fengyun 4A satellite T_(BB) data to analyze the rainstorm process.The results show that this weather process occurred in a favorable large-scale circulation background,and was affected by the shear line,which was finally generated by the train-shaped convective cloud cluster.From July 5 to 8,due to the adjustment of atmospheric circulation in the middle and high latitudes of Asia and the collapse of the obstructive high pressure of Lake Baikal,the cold air in the middle and high latitudes continued to advance southward,and the warm and humid airflows from the northward in the Yangtze River converged.The occurrence and development of heavy rain,in addition,the low-altitude southwest jet stream provides sufficient water vapor to strengthen and tilt the upper-level jet stream.The high-level jet stream meets over the middle and lower reaches of the Yangtze River,forming a strong upper-air convergence and low-altitude divergence,which makes the already strong upward movement extend to the upper troposphere.Through the analysis of the above-mentioned various reasons,it can be concluded that under various favorable circulation background conditions,the"train effect"of the mesoscale convective system is the direct cause of this heavy rain.