2011年4月17日广东强冰雹天气过程的成因及特征分析

ANALYSIS OF THE CAUSES AND CHARACTERISTICS OF A STRONG HAIL WEATHER PROCESS ON APRIL 17,2011 IN GUANGDONG PROVINCE

利用广州新一代多普勒雷达资料和Micaps资料,对广东省2011年4月17日强冰雹天气过程进行分析,揭示了强对流天气的环流形势和影响系统,着重分析了各种有利于大冰雹生成的因素和回波特征。研究发现:(1)过程发生在高层有急流、高空槽和切变线、地面有锋面低槽的环流形势下,属西江流域前汛期强对流天气类型的复合型。冰雹发生区域的低层垂直风切变较大,达-4.8×10-3/s。(2)当CAPE突增,SSI>200、K>35℃、Si<0℃时,预示强对流天气发生。(3)边界层辐合线为对流发展提供动力因素,同时大气不稳定和较高的CAPE造成雹暴的迅速发展。(4)本次雹暴几乎具有强烈对流风暴的所有回波特征:反射率因子图上的弓形回波、后侧入流缺口、悬垂结构、有界弱回波区、三体散射,径向速度图上的中气旋及中层径向辐合。(5)雹暴的回波顶高与最大反射率因子演变趋势基本相同,有几次跃增且同步。降雹前最大反射率因子及其高度均出现突降。VIL的跃增特性对于判断冰雹的增长非常有效。(6)本次过程具备适宜冰雹生长的0℃和-20℃层高度条件,且回波核心区高度扩展到-20℃层以上。VIL密度>4 g/m3和上干下湿的垂直分布十分利于大冰雹的产生。(7)三体散射特征可作为发布冰雹预警重要指标。

Using the data of the next-generation radar in Guangzhou and Micaps, a hail weather process on April 17, 2011 in Zhaoqing, Guangdong province was analyzed with the focus on the circulation and affecting systems, especially the factors favorite for large hail and radar echo. The results are as follows. （1） There were an upper-level jet and wind shear and though that combined with a surface front, and it was a typical situation for the annually first raining season convection in the Xijiang River basin. The low layer vertical wind shear reached -4.8×10^-3/s. （2） CAPE increased suddenly, with SSI〉200, K〉35 ℃ and Si〈0℃, indicating that there would be severe convection. （3） A boundary convergence line drove the development of convection factors, while the instable atmosphere and high CAPE result in the rapid development of the hailstorm. （4） The storm shows many significant features of severe convection, such as a bow echo, rear influx dent, suspension, BWER, three-body scatter spike（TBSS） in base reflectivity, and meso-cyclone and MARC in radical velocity. （5） The storm echo＇s top height and maximum reflectivity have basically the same trend of evolution, and experienced a few jumps in general synchronization. DBZM and DBZM HT dropped dramatically before the hail storm appeared. The characteristics of the jump of VIL was effective to confirm the growth of hail. （6） There were favorite height conditions of 0 ℃ and -20℃ layer for the hail, and the height of severe echo reached above the layer of -20 %. The densities of VIL large than 4 g/m3, and the structure of a dry upper-level associated with a wet low-level are the good conditions for this large hailstorm. （7） The feature of three-body scatter spike（TBSS） can be taken as an important index in issuing warnings.