辽东半岛一次湿下击暴流过程分析

Analysis of a Wet Downburst in the Liaodong Peninsula

2020年9月11日辽东半岛南部发生了一次强对流天气,并出现了湿下击暴流,大连金州得胜站地面最大阵风达到21.7 m·s^(-1)。本文利用常规气象资料、大连多普勒天气雷达资料、欧洲中期天气预报中心第5代全球再分析资料和高分辨率中尺度数值模拟资料,对此次湿下击暴流天气过程的环流背景、对流风暴发生发展环境及其回波特征等进行分析。结果表明:(1)此次强对流天气发生在北上台风变性形成的高空冷涡东部西南风与东南风的切变线上,地面辐合线和低空急流是触发初始对流的直接系统,初始对流在高空辐散耦合作用下发展加强;对流系统西移登陆至地面冷池与其东部暖空气之间形成锋生带上,辐合抬升作用加强,促使对流系统组织化程度更高、强度更强。(2)高温、高湿、对流不稳定层结是对流系统发生发展的有利环境条件。强对流发生前,探空曲线“上干下湿”、呈“V”型分布,抬升凝结高度明显下降;湿下击暴流发生时,径向速度垂直分布为中层径向辐合、低层辐散;瞬时大风出现前后,大连多普勒天气雷达在高、低仰角均探测到超过45 dBZ强反射率因子缺口,高仰角强反射率因子缺口先于低仰角出现,通过监测高仰角强反射率因子的变化,对湿下击暴流有一定的预警作用。

On September 11,2020,severe convective weather occurred in the southern part of Liaodong Peninsula,and wet downbursts appeared.The maximum surface wind gust at Dalian Jinzhou Desheng station reached 21.7 m·s^(-1).By using conventional observation data,Dalian Doppler radar data,ERA5 data and high-resolution mesoscale simulation data,the circulation background,convective environment and echo characteristics of this wet downburst was analyzed.The results show as follow:(1)the major synoptic system is shear line made up of southwest and southeast winds located to the east of upper-level cold vortex transformed by north-moving tropical cyclone.The mechanisms of convective initiation are surface convergence line and low-level jet.Coupling upper-level divergence enhances initial connection development.The convection system moved westward and landed on the frontal zone between the ground cold pool and the east warm air,and the convergence lifting effect increased,promoting higher organization and more severe of the convection system.(2)The highly warm and moist surrounding air and the instability are favorable conditions for convection.Before convection occurred,the sounding shows dry air overlapping moist air and"V"pattern.The lifting condensation level decreases distinctly.During the wet downburst,radar radial velocity shows mid-altitude radial convergence(MARC),low-level divergence.Before and after the gale,high and low elevations all exhibits more than 45 dBZ reflectivity notch.The high reflectivity notch at high elevation appears prior to that at low elevation.Monitoring the changes of the high elevation reflectivity contributes to the early warning of wet downburst.