2020年梅雨期江苏两次龙卷过程环境背景和龙卷母风暴形态特征分析

Analysis of Environmental Conditions and Tornado Storm Features of Two Tornadoes in Jiangsu during the Meiyu Period in 2020

2020年6—7月,江苏省发生了两次龙卷事件,分别在6月12日高邮以及7月22日宿迁、连云港、盐城三市。利用观测与再分析资料对产生两次龙卷的雷达资料特征、天气背景和对流环境条件特征进行了对比分析。雷达回波显示产生两次龙卷的对流系统特征显著不同:6月12日是独立于主雨带回波外的离散单体,在高邮市产生了一个龙卷,持续时间较长;而7月22日产生龙卷的单体镶嵌于主雨带回波南端,生命史内跳跃式移动,影响了邻近的几个市县;但都有识别到超级单体特征。这两次龙卷均发生在我国东部龙卷最高发的地区和季节,天气尺度背景都为典型的梅雨期暴雨环流。产生龙卷的中尺度对流系统发生在地面暖锋南侧高低空急流耦合区域,不同之处在于前一次的系统稳定少动,后一次则相对发展更加快速且强烈。从对流环境条件来看,两次过程都有有利于龙卷发生的中等偏强的对流有效位能、较好的低层湿度条件以及强的低层垂直风切变条件,而7月22日的条件更加有利,抬升凝结高度105 m,0~1 km和0~6 km垂直风切变分别达11和26 m/s。

In June and July of 2020,two tornadoes occurred in Jiangsu Province,which were located in Gaoyou on 12 June and Suqian,Lianyungang and Yancheng on 22 July,respectively.The property in the above areas was damaged,and no one was killed.We use observation and reanalysis data to compare and analyze the weather background and convective environmental conditions that produced the two tornadoes in this paper.The radar echo shows that the characteristics of the convection system that produced the two tornadoes are significantly different:On June 12,there was a discrete unit independent of the echo of the main rainband,which produced a tornado in Gaoyou City and lasted a long time;while on July 22,the unit that produced the tornado was inlaid at the southern end of the main rain belt echo,it moved leaps and bounds in the life history,affecting several nearby counties.The both tornadoes occurred in the regions and seasons where tornadoes occur most in eastern China,and the synoptic-scale backgrounds are typical rainstorm circulation during the Meiyu period.The mesoscale convective systems that produce the tornados occur in the high-low-level jet coupling area on the south side of the ground warm front.The difference is that the previous system was stable and less moving,and the latter developed more rapidly and intensely.From the perspective of convective environmental conditions,both processes have moderate to strong CAPE,better low-level humidity conditions and large low-level vertical wind shear that are conducive to the occurrence of tornadoes,especially the conditions on July 22 are more favorable,with lower lifting condensation level of 105m and stronger 0−1 km and 0−6 km vertical wind shear of 11 m/s and 26 m/s,respectively.