2014年春季华南地区两次强对流天气过程对比分析

Comparative Analysis of Two Severe Convective Weather Processes in Southern China Area

基于常规观测、气象卫星和雷达等资料,利用WRF模式对2014年3月31日和5月17日发生在华南地区的两次强对流天气过程的水汽条件、不稳定层结、抬升触发机制、垂直风切变,以及分别造成不同程度灾害性天气的机制进行了对比分析。结果表明:1)两次强对流天气过程,均是在充足的水汽和不稳定层结条件下,由850 hPa切变线与地面锋面共同抬升触发而成。在移动过程中强对流前部和后部低层都存在有组织的上升和下沉运动,配合大气环境中有利的垂直风切变,有利于强对流系统内部不断触发新的对流单体生成,从而维持了两次强对流过程完整的回波形态和较长的生命史。2)在低层0—3km高度,两次强对流均存在风随高度顺时针旋转、垂直风切变,但3月31日过程的风随高度顺时针旋转更显著,风速增大更明显,垂直风切变更大。在移动过程中强回波后部均有冷池结构形成,但3月31日过程的冷池强度、分布范围和厚度都明显强于5月17日过程。这种显著差异,使得前者更有利于出现大风、冰雹等灾害性天气。归纳出的基于"配料法"的预报思路:在水汽条件充足、K指数大于38°C、CAPE大于1 400 J/kg、SI指数小于-2,有锋面、切变线等抬升触发条件存在的情况下,在华南地区需要考虑对流天气发生的可能;当低层0—3 km高度出现风向强烈顺时针旋转、风速增大、垂直风切变增强,并出现强冷池中心时,还需要考虑有组织的强对流天气生成,这有利于提前做好冰雹、大风预警预报。

Based on the conventional observation data,meteorological satellite data and Doppler weather radar data,the WRF model is used to analyze the water vapor condition,stratification stability,lifting mechanism,and vertical wind shear for two different severe convective weathers in southern China.The results show that:1)The two processes is triggered by the combined lifting of surface front and the 850 hPa shear line under the conditions of unstable stratification and sufficient water vapor.The organized ascending and descending movements in the front and rear of lower layer of the moving severe convection,with the favorable vertical wind shear,continuously trigger new convective cells hap inside of the moving severe convective system,thereby maintain the unbroken radar echo and a long life history for the two severe convective weather process.2)During the two processes,the wind direction rotates clockwise with height and vertical wind shears between 0-3 km above the Baiyun Airport.And the process is more intense in the process A.The cold pool exists at the back of strong radar echo during the two severe convective moving processes,which is much significantly stronger in the process A.Those differences make the process A more conducive to the emergence of gust,hail and other disastrous weather.3)Through these analysis,the forecasting ideascould sum up based on the ingredients-based methodology:under the condition of sufficient water vapor,when K index >38℃,CAPE >1 400 J/Kg,SI index<-2,and with the existence of cold front and shear line or other trigger conditions,the convective weather may happen in southern China area.When the wind direction rotates strongly clockwise,wind speed increases with strong vertical wind shear and the emergence of a strong cold pool center,the forecaster may need to consider the formation of organized severe convective weather,which is conducive to ahead of hail and gale warning.