祁连山南麓一次冰雹天气成因分析

Analysis of a Hailstorm at Southern Foot of Qilian Mountains

利用常规观测资料、中尺度加密气象站资料以及卫星和雷达产品等资料,对2015年7月13日出现在祁连山南麓的一次冰雹天气进行综合分析。结果表明:蒙古冷涡旋转过程中底部下滑的冷槽向东南方向移动引导高空冷空气和正涡度平流,配合地面辐合线共同影响,给祁连山区南麓地区带来此次冰雹天气;南北较大的湿度梯度与中低层冷空气的渗透,使得大气层结不稳定度加大,促使垂直上升运动加强,为强对流天气的发展提供了有利条件。卫星云图上出现的逗点状雹暴云团,是造成冰雹天气的主要中尺度系统。雷达回波强度图上回波具有典型冰雹结构特征;VIL值出现骤降和陡增的变化趋势,与降雹时间有一一对应关系。

Based on the conventional observation data,mesoscale intensive observation data,satellite and radar products and other data,a comprehensive analysis is made of a hailstorm occurred at the southern foot of the Qilian Mountains on 13 July 2015.The results show:During the process of the Mongolian cold eddy rotation,the cold trough that slid at the bottom moved southeastward to guide the advection of highaltitude cold air and positive vorticity,which,together with the convergence line on the ground,brought the hailstorm to the southern foot of the Qilian Mountains.The large humidity gradient in the north and south and the penetration of cold air in the middle and lower layers induced the greater instability of atmospheric stratification and promoted the stronger vertical upward movement,which provided favorable conditions for the development of severe convection weather.The comma-shaped hailstorm clouds in satellite images were the main mesoscale system causing hailstorm weather.The radar echo intensity map shows the hailstorm structure characteristics,and the VIL value shows a trend of sharp drops and steep increase,which has a one-to-one correspondence with the hailstorm time.