2019年6月17日河北张家口线状对流中的 龙卷环境场与雷达特征

Tornado Environmental Field and Radar Echo Characteristics During Linear Convection in Zhangjiakou of Hebei Province on June 17,2019

利用常规气象资料、NCEP FNL 1°×1°再分析资料以及卫星雷达资料,对2019年6月17日发生在张家口的一次与线状对流伴随的龙卷天气进行分析。结果表明:(1)龙卷天气发生在对流层中低层高能中心、强垂直风切变以及中层强风速区的环境中。(2)中低层强的正水平螺旋度、低层强辐合与高层强辐散配置为龙卷发生提供了有利的环境条件。(3)在对流不稳定区,边界层辐合线是对流的触发条件,弧状云线的发展加强和上冲云顶的识别分析有利于判断对流云团的发展趋势,对强对流的短临预警有重要参考意义。(4)通过雷达资料与风场反演分析,线状对流中的龙卷是由γ中尺度涡旋在低层强辐合与上升气流的拉伸下形成的。强辐合区主要位于3 km高度以下。

Based on conventional meteorological data,NCEP FNL 1°×1°reanalysis data,satellite data,and radar data,the article analyzes the reasons for the tornado that formed in the linear convection in Zhangjiakou City on June 17,2019.The results show that:(1)The tornado formed in the region of the troposphere with a high energy center,strong vertical wind shear,and strong wind velocity.(2)The strong positive horizontal helicity in the middle-lower layer,low-level convergence,and high-level divergence provided favorable thermodynamic and dynamic conditions for the occurrence of the tornado.(3)The convection was triggered by the boundary layer convergence line in the convective unstable region;moreover,the strengthening of the arc cloud line and the overshooting cloud top were important references for warning of the severe convection,which helped to estimate the development of the convection.(4)According to the radar data and wind field retrieval,the tornado came from the“γ mesoscale eddy”,which was affected by the low-level strong convergence and updraft.The region of strong convergence was mainly located below 3 km.