2018年8月13日天津静海龙卷的雷达特征和发生条件

Radar Characteristics and Occurrence Conditions of Jinghai Tornado in Tianjin on 13 August 2018

利用常规观测资料、地面自动气象站资料、多普勒天气雷达和风廓线雷达资料等,对2018年8月13日17:30左右发生在天津静海的EF2级龙卷天气进行分析,重点分析龙卷发生前后的环境背景条件、局地不稳定条件、触发抬升条件及雷达回波特征等。结果表明:这次龙卷天气发生在500 hPa高空槽东移、副热带高压加强西进及台风摩羯北上的过程中;龙卷发生前环境大气处于明显不稳定状态,对流有效位能为1797 J·kg^(-1)(对流抑制能量为0 J·kg^(-1))、0~6 km风矢量差约为14 m·s^(-1),且存在较低抬升凝结高度;同时龙卷发生地局地存在较大对流有效位能(最大值超过4000 J·kg^(-1))和较低抬升凝结高度,且龙卷发生前抬升凝结高度出现突降现象(最低降到897 hPa附近)。龙卷发生前后上下游两站近地层(0~1 km高度及以下)垂直风切变值均出现先迅速增大后又迅速减小的特征,且垂直风切变值的迅速减小是由上层开始并迅速向下,而0~1 km以上高度的垂直风切变值没有明显变化。多普勒天气雷达观测表明,龙卷回波单体尺度小(正负速度中心直径为2 km左右)、正负速度中心最大旋转速度为24 m·s^(-1)、垂直涡度为2.4×10^(-2)s^(-1),回波具有明显悬垂结构和有界弱回波区及龙卷涡旋(TVS)等特征,后侧低层入流也非常强,应是微超级单体龙卷。海风锋移动到本地与上游雷暴单体出流形成的阵风锋相遇发生碰撞,触发局地不稳定能量强烈释放、激发雷暴单体新生并发展为有组织的强雷暴单体,应是此次龙卷发生的直接触发条件。

Using conventional observation data,ground automatic weather station data,Doppler weather radar and wind profiler radar data,etc.,this paper analyzes the EF2 tornado that occurred in Jinghai,Tianjin at about 17:30 BT 31 August 2018.The focus is on the analysis of environmental background conditions,local instability conditions,trigger uplift conditions and radar echo characteristics,etc.before and after the occurrence of tornado.The results show that this tornado weather occurred when the 500 hPa high-altitude trough moved eastward,the subtropical high strengthened its westward movement and Typhoon Capricorn was moving northward.Before the tornado occurred,the environmental background conditions were obviously unstable,the CAPE value was 1797 J·kg^(-1)(CIN was 0 J·kg^(-1))and the wind vector difference in the height of 0-6 km was approximately 14 m·s^(-1) and there was lower lifting condensation level(LCL).At the same time,there was high CAPE(maximum value exceeded 4000 J·kg^(-1)),lower LCL.Before the tornado occurred,LCL showed a sudden drop(lowest to around 897 hPa).With the occurrence of tornado,the vertical wind shear values near the ground(0-1 km height and below)at both upwind and downwind stations showed the characteristics of rapid increase first and then rapid decrease.The rapid decrease of the vertical wind shear value started from the upper layer and descended rapidly,while the vertical wind shear value above the 0-1 km height did not change significantly.Doppler weather radar observations show that the tornado echo had a small individual scale(with a diameter of about 2 km at the positive and negative velocity centers),a maximum rotational speed of 24 m·s^(-1) at the positive and negative velocity centers,and a vertical vorticity of 2.4×10-2 s^(-1).The echo of this tornado had obvious overhanging structure,bounded weak echo zone and tornado vortex.Moreover,the low-level inflow at the rear side was very strong,so it should be a micro supercell tornado.The collision between the sea breeze front moving to the locale and the gust front formed by the upwind thunderstorm cell outflow triggered the vigorous release of unstable energy locally,stimulating the regeneration of thunderstorm cells,and developing into organized strong thunderstorm cells,which should be the direct trigger conditions for the occurrence of this tornado.