一次梅雨锋特大暴雨中尺度气旋和MCS的分析

利用自动气象站、多普勒雷达、FY4A、ECMWF模式、NCEP再分析资料，对2020年7月17—19日特大暴雨过程进行分析。结果表明：特大暴雨出现在安徽大别山附近和庐江两地，是中尺度气旋扰动环境下准静止的中尺度对流系统（MCS）以及MCS中准静止的涡旋状单体所产生。特大暴雨在高能量、强不稳定背景下，由中部和东部的中尺度气旋传播所致。中尺度气旋传播过程中单体不断新生、合并增强且移动缓慢，配合急流、辐合、干侵入、垂直环流等因素对组织化的MCS发展演变起到相当作用。低层切变线南侧到华南的西南急流，将水汽输送到安徽并在此有强烈辐合；高空、低空和超低空都存在急流，高低空急流耦合加剧MCS的强烈发展；地面辐合线是前期MCS的触发机制，伴随干冷空气的入侵，加大了大气的斜压性和MCS的对流不稳定；梅雨锋南北两侧都有垂直环流圈，即对流与高空急流之间通过对流加热在高空急流入口处产生热成风调整，维持梅雨锋的发展演变，强的上升下沉运动促进MCS的加强和降水的连续发生；大别山地形抬升和上游狭管效应是两地特大暴雨诱因。

Analysis of Mesoscale Cyclone and MCS about an Extraordinary Rain on Meiyu Front

Based on the automatic weather station, Doppler radar, FY4A, ECMWF model and NCEP reanalysis data, the extraordinary rain process from July 17 to 19, 2020, is analyzed. The results are as followings. The extraordinary rain occurred near Dabie Mountain and Lujiang County in Anhui Province, caused by the quasi stationary mesoscale convective system (MCS) and the quasi stationary vortex cell in MCS. The mesoscale cyclonic disturbance was composed of the shear line and cyclone. Under the background of high energy and strong instability, the extraordinary rain was caused by the mesoscale cyclone in the middle and east. In mesoscale cyclone propagation, the cell continuously produced, merged and strengthened, and moved slowly. The factors such as jet stream, convergence, dry intrusion and vertical circulation played an important role in the development and evolution of organized MCS. The southwest jet from the southern side of the low level shear line to South China transported water vapour to the Yangtze and Huaihe River Basin, where there was strong convergence. There were jets at the high, low, and ultra low levels, and the coupling of high and low level jets intensified the strong development of MCS. The surface convergence line was the trigger mechanism of MCS in the early stage. With the invasion of dry and cold air, the baroclinity of the atmosphere and the convective instability of MCS were increased. The surface convergence line was the trigger mechanism of MCS in the early stage. With the invasion of dry and cold air, the baroclinity of the atmosphere and the convective instability of MCS were increased. There were vertical circulation circles on both sides of the Meiyu front, that was, the convective heating between the convection and the upper jet generated thermal wind adjustment at the entrance of the upper jet stream to maintain the development and evolution of the Meiyu front, and the strong ascending and descending motion promoted the strengthening and falling of MCS and continuous occurrence of rain. The terrain uplift of Dabie Mountain and the narrow pipe effect in the upper reaches induced extraordinary rain in the two places.