Analysis of mesoscale characteristics of a thunderstorm gale in Chengdu

Based on data from conventional observations, intensive automatic weather stations, automatic station 5-minute, weather radar and wind profile radar network, a thunderstorm gale in Chengdu during the night of 27 July 2017 was analyzed. The main results are as follows. The event occurred under the influence of subtropical high and the shear line. Several factors such as surface convergence, weak vertical wind shear, unstable stratification and large convective available potential energy were favorable to the development of the thunderstorm gale. The thunderstorm gale was caused by the highly organized multi-cell storm. Radar echoes had characteristics of narrow-band echo, rapid declines of the core of reflectivity factor, inflow in the front side, outflow flows in the back side and mid-altitude radial convergence. The characteristics had a significant importance in the monitoring and warning of the thunderstorm gale. The thunderstorm high and strong cold center had played an important role in the formation and maintenance of the thunderstorm gale. During the thunderstorm gale, the wind direction change was accompanied by the instantaneous wind speed increase, but the wind direction change occurred about 5 minutes earlier than the maximum instantaneous wind speed, and the appearance of the mesoscale cyclone convergence was 15 minutes earlier than the appearance of the maximum instantaneous wind speed. The larger slope the gust front was, the greater the updraft in the front side was. The rear vertical wind speed change of the gust front had been behind the horizontal wind speed.