2019年辽宁开原龙卷风观测事实分析

利用加密自动站、FY-4A卫星及多普勒雷达等观测资料,对2019年7月3日辽宁开原突发龙卷天气进行分析。结果表明:在冷涡减弱阶段,中纬度冷空气活动频繁,冷涡底部500 hPa与850 hPa的短波槽垂直分布,利于辽宁北部对流不稳定加强。FY-4A可见光云图显示,开原龙卷生消迅速,有明显的上冲云顶。雷达反射率因子特征是,对流单体合并形成超级单体,出现连续体扫的中气旋、并伴有钩状回波,三维显示出现空洞结构;强回波区向移动方向一侧倾斜、垂直剖面存在穹隆结构和有界弱回波区时,钩状回波处最容易产生龙卷;空洞的位置与中气旋和钩状回波中心区相吻合,表明超级单体在此处产生强烈涡旋,有利于漏斗云脱离母体向地面发展。速度产品上出现对称的正负速度区,旋转速度持续增大,且正负速度区不断向下发展,低仰角探测到紧邻的速度对时,中气旋相应也出现向下延伸和迅速收缩,预示龙卷的发生。东北冷涡以及蒙古气旋前侧低压带、低层干冷空气侵入导致锋生等动力条件,是辽宁北部对流的天气尺度和中α尺度的触发机制。

Observational Analysis of Tornado in Kaiyuan of 2019

Using the observation data of automatic stations,the FY-4A satellite data and the Doppler radar data,the sudden strong convective weather are analyzed in northern Liaoning on July 3th,2019.Results show that in the context of the weakening stage of the cold vortex,the cold air activity at mid-latitudes is frequent,and the short wave troughs at the bottom of the cold vortex on the 500hPa and the 850hPa levels form a forward-inclined structure,which is conducive to the strengthening of the convection instability in northern Liaoning.The tornado in Kaiyuan generates and disappears rapidly,and clear overshooting cloud tops on the visible images of the FY-4A satellite.The radar reflectivity factor is characterized by the combination of convective cells to a supercell,the continuous mesocyclone,the hook echo,and the three-dimensional display of a hollow structure;When the strong echo area is inclined to the side of the moving direction,there is a dome structure and a bounded weak echo area in the vertical section,and the tornado is most likely to occur in the hook echo area;The location of the cavity coincides with the central region of the mesocyclone and the hook-shaped echo,indicating that the supercell has a strong vortex there,which is conducive to the movement of the funnel cloud from the parent body to the ground.There are symmetrical positive and negative speed zones on the radar speed product.The rotation speed continues to increase,and the speed zones develop downward continuously.When the adjacent speed pair is detected at a low elevation angle,the mesocyclone also extends downward and shrinks rapidly,indicating the occurrence of tornado.The cold vortex in the northeast of China,the low-pressure zone in front of the Mongolian cyclone,and the invasion of cold and dry air on low levels caused the frontogenesis and other dynamic conditions,which are the triggering mechanism of the convection from Jilin to northern Liaoning on the weather and the middleαscale.Whereas the local heating near Kaiyuan generates updrafts,and the decrease of the surface pressure enhances the cyclonic convergence of the wind field and the development of the ascending movement,which are the triggering mechanism.