一次下击暴流风暴的成因和结构特征分析

Analysis of the causes and structural characteristics of a downburst storm

2017年7月28日四川省东北部出现了一次罕见的湿下击暴流大风天气过程。本文利用地面自动站、雷达、卫星等观测资料以及FNL数据、视频资料,对下击暴流风暴的成因和结构特征进行研究分析。研究表明:此过程发生前,对流层中低层的环境温度及其直减率均达到同期历史极端值,有利于雷暴大风类型中尺度对流风暴的形成;此次下击暴流,主要由阵风锋与地面中尺度辐合线相交后触发,阵风锋水平涡度不断输入对流系统内,产生正的相对风暴螺旋度,利于对流风暴持续发展到较高高度,为下击暴流的产生提供条件;下击暴流发生前的对流风暴,在视频截图和反射率因子剖面图上均表现为悬垂倾斜结构,倾斜方向与对流层中层平均风向较一致;对流风暴中层的气旋性涡旋结构特征可作为下击暴流的预警指标之一。

There was a rare wet downburst in the northeastern part of Sichuan province. Based on the observation data of ground automatic station, radar and satellite, and FNL data and video data, the causes and structural characteristics of the downburst storm were analyzed in detail. The results show that the ambient temperature in low troposphere and lapse rate reached the same period in the history of extreme value, facilitates the emergence of mesoscale convective storm types in thunderstorm. The formation of convective storm of downburst winds, mainly by the gust front and the ground in triggering the convergence line intersection, gust front horizontal vorticity input of convective system, generate positive storm relative helicity, conducive to the sustainable development of convective storm to a higher height to downbust conditions. The convective storm before the onset of the storm is shown in the video capture and reflectivity, and the tilt direction is consistent with the mean wind direction in the middle troposphere. The characteristics of the cyclonic vortex in the middle of the convective storm can be used as one of the early warning indicators of the downburst.