Mesoscale analysis of a downburst process in Yichang three gorges dam area on 29 July 2017

Based on conventional observation data, regional station observation data, EC reanalysis data, FY-2G satellite data, and radar data, a downburst in Yichang on 29 July 2017 was analyzed. The results show that: (1) The downburst occurred at the edge of subtropical high, the convection in the north of Yichang was triggered by cold air, and the convection in the central section was triggered by the uplift of mountain terrain in the west of Yichang. (2) the downburst was accompanied by the abrupt rise of air pressure, the sudden drop in air temperature, the sudden change of wind direction, and the sudden increase of wind speed. The strong and rapid cold outflow has the most obvious influence on the occurrence of the gale. (3) Satellite cloud image shows that the location of gale is basically in the area with the largest cloud top brightness temperature gradient in the front of cloud cluster propagation direction. (4) The process is characterized by a typical pulse storm and the initial thunderstorm. The echo intensity is strong, the height is 4~6 km, the echo shape is vertical, and there are obvious radial convergence characteristics in the middle layer about 10 minutes before the surface gale appears. (5) The echo is strengthened twice in the process of moving and developing, one is echo merging enhancement and the other one is strengthened by local thermal and dynamic convergence near the Three Gorges Dam Area, and blocked by the Yangtze River Valley twice and the high blocking effect. The echo moves slowly in the Yangtze River Valley, so it can last for a long time.