成都一次雷暴大风的中尺度特征分析

Analysis of mesoscale characteristics of a thunderstorm gale in Chengdu

利用常规观测资料、加密自动站资料、自动站5 min资料、天气雷达资料和风廓线雷达组网资料,对2017年7月27日夜间出现在成都地区的一次雷暴大风天气过程进行分析,结果表明:本次过程发生在副热带高压和切变线共同影响下,地面辐合线、弱垂直风切变、层结不稳定和较大的对流有效位能为雷暴大风的发生提供了有利的环境条件。此次雷暴大风天气过程是由多单体风暴产生的;雷达回波具有窄带回波、反射率因子质心快速下降、风暴前侧出流、后侧入流和中层径向辐合等特征,这些特征对监测和预警雷暴大风有很好的指示意义。雷暴高压和强冷中心对雷暴大风的形成和维持有着重要作用。在大风过程中,风向突变伴有瞬时风速增大,但风向突变出现时间较最大瞬时风速出现提前了5 min左右,中尺度气旋式辐合的出现时间较最大瞬时风速有15 min的提前量。阵风锋坡度愈大,前侧上升气流坡度愈大;阵风锋后部的垂直风速变化落后于水平风速的变化。

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.