广东两次超级单体导致不同类型强风天气对比分析

A Comparative Study on Two Different Types of Gale Events Caused by Supercell in Guangdong

2019年4月11日珠江三角洲、4月13日湛江徐闻分别发生了由超级单体引起的强雷暴大风、强龙卷灾害天气过程。利用多源观测资料对比分析两次过程的天气形势、环境条件、风暴结构、对流触发以及强风的形成机制,结果表明:强雷暴大风发生在低空切变线和地面冷锋南压的斜压锋生类天气形势下,而强龙卷发生在偏南暖湿气流强迫天气背景下。两者均发生在高能、强0~6 km深层垂直风切变、低抬升凝结高度及上干下湿的大气环境中,但11日0~1 km低空垂直风切变较小,中层干层更为显著(700~400 hPa平均温度露点差为29.2℃),更有利于产生强下沉气流从而导致强雷暴大风,而13日强的0~1 km低层垂直风切变,有利于强龙卷发生。11日强雷暴大风出现在超级单体强回波核心,低层中气旋强度较弱且水平尺度较大(6~7 km),中气旋较浅薄(伸展≤2 km),而13日强龙卷出现在钩状回波顶端,低层中气旋强度更强且尺度小(约2 km),中气旋更深厚(伸展至6 km),并伴有龙卷涡旋特征;11日强雷暴大风发生期间,中气旋垂直涡度维持在10^(-2) s^(-1)量级,而13日强龙卷触地前后,低层中气旋垂直涡度突增至10^(-1) s^(-1)量级,比强雷暴大风大一个量级;11日风暴内强下沉气流在地面形成大面积强冷池,是强雷暴大风产生的重要原因,而13日地面几乎饱和的大气湿度及不太强的下沉气流,有利于强龙卷的发生。

One supercell triggered severe thunderstorm gales in the Pearl River Delta on 11 April 2019 and another supercell induced an EF3 strong tornado in Xuwen County of Zhanjiang City on 13 April 2019.Based on multi-source observations,the synoptic situation,ambient conditions,structure of the storm,triggering characteristics of convective storm,and formation of the severe thunderstorm gale and tornado in the two events are comparatively analyzed.The results are as follows.The severe thunderstorm gales occurred under the southward shear line in the lower layers and the surface cold front,which was classified as the baroclinic frontogenesis severe convection.The strong tornado was the southerly warm advection forcing sector severe convection.The ambient conditions in both days were characterized by high energy strong 0-6 km vertical wind shear,low lifting condensation height and the stratification of dry in the upper level and wet in the lower level.But the sounding at Qingyuan Station on 11 April shows that 0-1 km vertical wind shear was small and average depression of the dew point was 29.2℃in middle levels.This condition was favorable for the formation of strong downdraft.However,the sounding at Haikou Station on 13 April shows that strong 0-1 km vertical wind shear was favorable for the tornado.On 11 April,the thunderstorm gales were located at the core of the supercell.The low-level mesocyclone was weaker and had a larger diameter of 6-7 km.The rotation depth of mesocyclone was below 2 km.On 13 April,the tornado occured at the top of the hook echo accompanied by low-level intense mesocyclone with the minimum diameter of 2 km and tornadic vortex signature.The rotation depth mesocyclone was up to 6 km.Vertical vorticity remained unchanged at the order of 10^(-2) s^(-1) before and after the thunderstorm gales.However,the tornado occurred during the magnitude of low-level mesocyclone vertical vorticity increased to be 10^(-1) s^(-1) rapidly,which was an order of magnitude larger than the vertical vorticity of strong thunderstorm gale event.The strong downdraft of the storm produced a large area of intense cold pool on the ground on 11 April,which was favorable for the formation of thunderstorm gales.The saturated atmosphere on the ground and the less strong downdraft of the storm were conducive to the occurrence of strong tornado.