桂西北一次超级单体风暴过程的分析

A Case Study on Supercell Storm of Hail in the Northwest of Guangxi

本文利用常规观测资料和多普勒天气雷达资料,对2009年4月12日发生在广西西北部的大范围冰雹天气进行分析,得出以下结论:(1)导致冰雹发生的天气系统是高空低涡和低层切变线,冰雹发生前上午百色探空站有中等对流有效位能、上干下湿层结结构、强的深层垂直环境风切变,速度矢图上低层强的顺时针旋转曲率,已经具备强对流潜势发生条件。(2)超级单体右前方的低层反射率因子呈现明显的钩状回波,是超级单体风暴的典型特征之一。反射率因子垂直剖面呈现出典型的有界弱回波区、回波悬垂和回波墙。最大的回波强度出现在沿着回波墙的一个竖直的狭长区域,其值超过65 dBz。相应的中低层径向速度图呈现一个中等强度的中气旋,旋转速度达到22 m·s-;垂直累积液态水含量和密度分别超过70kg·m^(-2)和5 g·m^(-3)。(3)高空低涡正涡度区、高CAPE值、地面辐合线在右江河谷滞留以及特殊地形作用,是多个对流单体沿相似路径移动的主要原因。

Based on the routine observation data and the Doppler weather radar data,the large-scale hail in the northwest of Guangxi is analyzed.The results show that;（1） The systems csusing hail are upper-air-vortex and low-level shear line.Although the CAPE was moderate before the hail,it has necessary conditions for the severe convection potential occurrence such as the stratification of upper dry and lower wet, strong environmental wind shear and the strong clockwise curvature at low levels.（2） The low-level reflectivity on the right front of the supercell shows a typical hook echo and it is a typical feature of super-cells. Along the inflow direction and through the strongest echo,the reflectivity shows typical BWER （Boundary Weak Echo Region）,overhang echo and echo wall.The strongest echo is within a vertical narrow region along the echo wall and can be more than 65 dBz.The corresponding radial velocity in the lower atmosphere has a moderate meso-scale vortex street and its rotation speed can be 22 m？s^（-1）.Meanwhile the VIL exceeds 70 kg？m^（-2） and its density exceeds 5 g？m^（-3）.（3）The positive vorticity at upper levels, high CAPE value,convergence line on the ground stranding in the Youjiang Valley and the special terrain are the main causes for many convection cells moving along similar paths.