2019年7月3日开原龙卷形成环境背景及机理探究  

Environmental Background and Formative Mechanisms of a Tornado Occurred in Kaiyuan on 3 July 2019

作　　者：袁潮 王式功[1] 马湘宜 杨磊 陈丽楠 YUAN Chao;WANG Shigong;MA Xiangyi;YANG Lei;CHEN Linan(College of Atmospheric Sciences,Chengdu University of Information Technology,Chengdu 610225,Sichuan,China;Panjin Meteorological Bureau,Panjin 124010,Liaoning,China;Liaoning Meteorological Disaster Warning Center,Shenyang 110166,Liaoning,China;Liaoyuan Meteorological Bureau,Liaoyuan 136200,Jilin,China)

机构地区：[1]成都信息工程大学大气科学学院,四川成都610225 [2]辽宁省盘锦市气象局,辽宁盘锦124010 [3]辽宁省气象灾害监测预警中心,辽宁沈阳110166 [4]吉林省辽源市气象局,吉林辽源136200

出　　处：《高原气象》2021年第2期384-393,共10页Plateau Meteorology

基　　金：气象预报业务关键技术发展专项(YBGJXM20201A-06);中国气象局预报员专项(CMAYBY2020-026)。

摘　　要：利用高时空分辨率多源观测资料对2019年7月3日辽宁省开原市一次EF4级超强龙卷过程进行分析。结果表明:(1)此次龙卷过程发生在高空东北冷涡西南侧的天气背景之下,低层次天气尺度横槽抬升作用是减小对流抑制的关键机制,起源于干线的地面辐合线与雷暴下沉出流所产生的中尺度伪冷锋相遇是龙卷风暴的触发机制。(2)超低空急流、高空干空气平流以及午后地面太阳辐射加热共同作用是造成局地热力和动力不稳定迅速增大的原因,较大的对流有效位能、低层湿度、垂直风切变及风暴相对螺旋度为龙卷母云的生成提供了有利的环境条件。(3)多普勒雷达呈现出经典超级单体龙卷特征,钩状回波位于超级单体右后侧,龙卷生成于钩状回波边缘。径向速度场显示气旋式旋转首先出现在低层,龙卷的加强发展伴随低层中气旋和明显的相邻方位角切变。雷达反射率三维立体图像可见龙卷中心上方存在强回波的凹陷区。(4)超低空急流加强低层水平涡度输送,两条辐合线相遇形成的中尺度气旋性环流为龙卷提供初始的垂直涡度来源,在上升气流的拉伸作用下,垂直涡度收缩助力龙卷形成。In this study,an EF4 scale tornado occurred in Kaiyuan on 3 July 2019 was investigated through several high spatio-temporal resolution observations. The results show that:(1)The tornado was under the southwest side of a cold vortex over Northeast China,a sub-synoptic scale transverse trough at low level was a destabilizing mechanism for convection development,while the encounter of the convergence line that originated from a dry line and a mesoscale pseudo cold front was the trigger mechanism of the tornado storm.(2)The rapid increase of thermal and dynamic instability are caused by the comprehensive effects of ultra low level jet,high level dry airflow and solar radiation heating. The large value of CAPE,relative humidity at low-level,vertical wind shear and storm relative helicity(SRH)are conducive to the formation of the tornadic storm.(3)The tornado was generated at the edge of a typical hook-shape supercell echo. Cyclone rotations first appeared in the lower layers,and the development of the tornado was associated with the mid-lower cyclones and significantly adjacent azimuthal velocity shear. A weak echo hole(WEH)could be found above the center of tornado in 3-D image of the radar reflectivity.(4)The ultra low level jet enhanced the transport of horizontal vorticity. The mesoscale cyclonic circulation formed by the meeting of the two convergence lines provided an initial source of vertical vorticity for the tornado. The tornado was generated by the contraction of vertical vorticity under the stretching of the updraft.

关 键 词：龙卷 超低空急流 干侵入 地面辐合线 龙卷形成 

分 类 号：P458.3[天文地球—大气科学及气象学]