Initiation and evolution of MCS of Meiyu frontal heavy rain event in the complex terrain of northeast Hubei

Based on ERA5 reanalysis data, radar data in Hubei Province and MICAPS observation data, the Meiyu frontal heavy rain event occurred in Northeast Hubei on July 16 2020 was analyzed. The results show that:(1) The heavy rain event exhibited a northwest-southeast zonal distribution along the mountain range with long duration, high rainfall intensity and concentrative location. The meso-β scale convective characteristic of heavy rainfall was obvious. (2) The surface Meiyu front and the shear convergence system between 925 and 500 hPa formed a north dipping shear system. This shear system was stable in Northeast Hubei during the day of 16 to provide dynamic forcing, water vapor and thermal conditions for the occurrence and development of mesoscale system and heavy rain. (3) In the development stage of MCS, there are two kinds of backward propagation. One is the backward propagation of convective cells, and the other is the backward propagation of convective rainbands. These two kinds of backward propagation form several short parallel convective rainbands in a nearly NE-SW direction. The short rainbands move along MCS to form a northwest-southeast "band-training". In the mature stage of MCS, the moving direction of cells is consistent with MCS to form a "train effect". (4) A cyclonic shear was formed near Tongbai Mountain and a meso-β convergence line was formed near Chenxiang station due to the complex terrain of northeast Hubei, which are favorable for the formation of new convective rainbands on the west or northwest side of MCS. The terrain blocking effect of Tongbai Mountain and western of Dabie Mountain makes the cold pool form cold outflow. It strengthens the convergence of 925 hPa air flow on the south side of the mountain, which is favorable for the regeneration of the convective cells on the southwest side of the convective rainbands.