河北张家口一次超级单体龙卷雷达回波特征分析

Analysis of Radar Echo Characteristics of a Supercell Tornado in Zhangjiakou,Hebei Province

利用ERA5再分析资料、雷达资料以及北京VDRAS资料,对2021年7月1日发生在张家口的一次与超级单体伴随的龙卷天气特征进行分析。结果表明:(1)此次龙卷天气发生在高空冷涡的东南象限、低空切变线前侧暖区及地面辐合线附近。(2)雷达资料分析显示在超级单体的南侧产生了此次龙卷,龙卷过程中超过50 dBz的高度在6 km以下,强核中心在3 km以下,为低质心的对流系统,反演的风场上在低层1 km高度存在闭合的气旋性环流。(3)北京VDRAS资料分析表明低层强辐合与高层强辐散配置、中低层强的正风暴相对螺旋度为龙卷发生提供了有利的环境条件;垂直速度分布显示龙卷生成地存在强上升运动,其两侧均存在下沉运动;扰动温度的垂直分布表明4 km以下存在负中心,4 km以上存在正中心。

Based on the ERA5 reanalysis data,Doppler radar data and Beijing VDRAS data,a tornado with a supercell that occurred in Zhangjiakou on July 1,2021,is analyzed.The results show that:(1) The tornado occured in the southeast quadrant of the cold vortex,the warm region in front of the shear line and near the surface convergence line.(2) The analysis of radar data shows that the tornado was generated on the south side of the supercell.During the tornado process,the height of more than 50 dBz was less than 6 km,and the strong core centre was less than 3 km,which was a convective system with a low centroid centre.In the wind field retrieved by radar,there was a closed cyclonic circulation at the lower level of 1 km.(3) The analysis of VDRAS data in Beijing shows that the strong convergence in the lower layer,divergence in the upper layer and the strong positive storm-relative helicity in the middle and lower layer provided favourable environmental conditions for the tornado occurrence.The vertical velocity distribution shows that there was strong upward movement and sinking velocity zone on both sides of the tornado.The vertical distribution of the disturbance temperature indicates that there was a negative centre below 4 km and a positive centre above 4 km.