2017年8月13日长江中上游强降水云系形成分析
Analysis of Formation of Heavy Precipitation Clouds in the Upper and Middle Reaches of the Yangtze River on 13th August, 2017

本文利用ERA-5再分期资料、每日降水资料及国家卫星气象中心发布的云图资料以及美国NoAA网站发布的Himawari云图资料，对2017年8月13日长江中上游强降水过程云系的形成从实况、环流形势以及热力、动力和水汽诊断方面进行了分析，发现与长江中上游地区强降水过程对应的云系落区主要位于云系北侧，达到大暴雨或特大暴雨等级；此次降水云系主要由华南到东海一带上空多云团演变发展形成；高低空环流形势上，地面有一准静止锋位于长江流域，锋前形成江淮气旋；500 hPa位势高度上表现为欧亚中高纬度呈两槽一脊的经向环流形势，副热带高压北抬西伸，冷暖气流于江淮流域交汇，低层有加强的偏东气流将大量水汽输送至我国南部地区，江淮流域建立的低涡、切变线形势，低涡、切变线是准静止锋对应云系形成和维持的基础；热力方面，中纬度地区有物质以及能量密集交换，动力方面，垂直速度场上东海–华南一带有三个垂直上升运动大值区，高低层散度与之配合，加强了上升运动，对应云系的发展；水汽方面，700 hPa上青藏高原南部到东海一带为相对湿区，云系即生成在该湿区一带，之后相对湿度中心减弱，此时云系新生、发展也减弱，主要沿着湿区想东北方向移动，且在海上的湿中心加强。
In this paper, the formation of heavy precipitation clouds in the upper and middle reaches of the Yangtze River on 13th August, 2017 was analyzed from the perspectives of the actual situation, circulation, and the diagnosis of heat, power and water vapor by weather map released by the Central Meteorological Observatory website, daily precipitation data, cloud map data released by the Satellite Meteorological Center, and Himawari cloud data published by the US NoAA website. It is found that the cloud system falling area corresponding to the heavy precipitation process in the upper and middle reaches of the Yangtze River is mainly located on the north side of the cloud system, reaching the level of heavy rainstorms or extraordinarily heavy rainstorms, and the precipitation cloud system is mainly formed by the evolution and development of a cloudy group over the South China Sea to the East China Sea. In the situation of high and low air circulation, there is a quasi-stationary front on the ground located in the Yangtze River basin, and the Jianghuai cyclone is forming in front of the front. The 500 hPa geopotential height shows a meridional circulation pat-tern with two troughs and one ridge at middle and high latitudes in Europe and Asia. The subtropical highs stretch north and west, and the cold and warm air flow at the junction of the Yangtze and the Huaihe valleys. The enhanced easterly air flow at the lower level transports large amounts of water vapor to southern China. The vortex and shear line conditions established in the Yangtze and Huaihe River basins, and the low vortex and shear line are the basis for the formation and maintenance of the quasistationary frontal cloud system. In terms of thermal power, there are material and energy-intensive exchanges in midlatitude regions, and in terms of dynamics, the vertical velocity field on the East China Sea and South China Sea has three large areas of vertical upward movement, and the high and low levels of divergence