2017年7月29日宜昌三峡坝区一次下击暴流过程的中尺度分析

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

利用常规气象观测资料、区域站观测资料、EC再分析资料、FY-2G卫星资料和雷达资料,对2017年7月29日湖北宜昌一次下击暴流过程进行了中尺度分析。结果表明:(1)此次下击暴流过程发生在副热带高压(以下简称副高)边缘,宜昌北部对流由冷空气触发产生,中部对流由冷空气绕流产生的偏东气流受宜昌西部山区地形抬升触发产生。(2)下击暴流过程中伴随着气压陡升、气温骤降、风向突变、风速骤增的现象,气压突增和风向突变比风速骤增提早10 min左右出现。(3)卫星云图显示大风出现的位置基本上在云团传播方向前沿云顶亮温梯度最大的区域。(4)本次过程呈典型的脉冲风暴特征,初始雷达回波强度较强,高度位于4~6 km,回波形态直立,且在地面大风出现前10 min左右有明显的中层径向辐合特征(MARC)。(5)回波受长江河谷地形阻挡以及副高的阻挡作用,在长江河谷移动缓慢,因此维持时间较长,并且出现两次加强,一次为回波合并加强,一次在三峡坝区附近受局地的热力和动力辐合作用加强。

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.