一次超级单体雹暴的中尺度对流特征和形成条件分析

Analysis of Mesoscale Convective Characteristics and Environmental Conditions of Supercell Hailstorm

北京2014年7月16日一次超级单体风暴造成了罕见大冰雹、短时大风和局地暴雨等强天气。利用雷达、自动站、探空、基于雷达观测的四维变分同化系统(VDRAS)等资料针对中尺度对流特征和形成条件进行了分析。结果表明:1)这次超级单体风暴有穹窿回波和悬垂、中气旋、三体散射等典型大冰雹雹暴云特征。2)降雹属于西北气流型,雹区出现在低层切变线和地面辐合区(辐合线)附近,低层很好的水汽条件是这种类型下降雹的必要条件。此外,1500 J/kg以上的高CAPE以及上干下湿的不稳定层结、850 hPaθse 360 K的高能舌中心均有利于强对流的发生;“喇叭口”型探空、适宜的0℃层和-20℃层高度以及这两个特性层之间厚度变小是大冰雹出现的典型环境。3)有利的地形、雷暴下山冷池增强导致前侧辐合增强是超级单体发展并向南移动的有利条件。

A supercell storm caused unusually large hail,wind gust,and local heavy rain in Beijing on 16 July 2014.The mesoscale convective characteristics and formation conditions were analyzed with Doppler weather radar,automatic weather station(AWS)data,radio sounding,and the four-dimensional variational radar assimilation system(VDRAS).The results showed that:(1)supercell storm had three-body scattering,echo overhang,mesocyclone,and other typical large hailstorm cloud characteristics.(2)It belonged a northwest flow type.The hailstorm area appeared near the low-level shear line and the boundary layer convergence line.Favorable thermal dynamical and water vapor conditions,vertical wind shear,unstable layer("horn"type of sounding with high CAPE above 1500J/kg),and 360Kθse high-energy tongue centered at 850 hPa;Suitable 0℃layer and-20℃layer height with the thickness between the two characteristic layers reduced were conducive to the occurrence of large hail in Beijing.(3)Favorable terrain and front side convergence enhancement as a result of thunderstorm cold pool enhancement when it moved to plain promoted supercell development and its southward movement.