2013年8月河南三次西南气流型强对流天气分析

Analysis on Three Severe Convective Weather Events of Southwest Flow Type in Henan August 2013

利用常规气象观测、区域加密自动站、NCEP/NCAR逐6 h 1°×1°再分析资料和多普勒雷达探测资料,对2013年8月河南三次西南气流型强对流天气的环境条件、回波特征和成因进行了分析,结果表明:(1)三次强对流天气均发生在中纬度低槽和副热带高压相互作用,河南高、中、低层受一致西南气流影响的环流背景下,地面存在温度和露点温度梯度及辐合线,大范围强对流天气是在高空槽动力作用和地面辐合线的触发作用下,使得不稳定能量释放而引起。(2)三次强对流天气对流层中下层有比较深厚的暖湿层结,热力和水汽条件充分,对流层中上层有明显干层,从而形成了低层暖湿、上层比较干冷的对流不稳定大气层结。强的垂直风切变位于对流层中下层,对流有效位能非常大,配合一定的动力抬升条件,有利于超级单体和飑线的发生和发展。综合来看,8月1日不稳定、水汽、垂直切变和动力条件最强,1 1日次之,7日相对较弱。强对流形成条件的强弱对对流系统的组织结构有一定影响。(3)雷达和自动站加密观测资料显示,强天气过程初始阶段,主要表现为多单体回波结构,初始对流都在河南西南部和西部到山西南部的辐合线、干线附近生成,随后逐渐加强,形成多单体回波群(其中部分发展成为非典型超级单体)。成熟阶段,都发展成为线状对流系统,8月7日在河南北部形成由强对流单体组成的不连续的东北西南向线状对流回波,8月1和¨日在河南黄淮平原和华北平原高温高湿环境中形成了有组织的飑线。飑线东移过程中其前侧不断有暖湿空气辐合上升、后侧冷空气下沉辐散,互为对峙的上升和下沉气流相互作用是飑线得以发展和维持的主要原因。(4)对流层中低层相对深厚的暖湿层结及其以上的干层是盛夏西南气流形势下河南强对流天气预报值得关注的内容,CAPE、△θ_(se(850-500))、△T_(850-500)、K指数、对流层中低层垂直风切变等对西南气流超级单体、飑线等强风暴的形成具有很好的指示意义。

Using conventional meteorological observations,regional dense automatic weather station data,NCEP/NCAR 1°× 1° reanalysis data with 6 h interval and Doppler radar data,this paper analyzed environmental conditions,echo characteristics and causes of three severe convective weather processes of southwest flow type in Henan in August 2013.The results show that：（1） Three severe convections all occur in the interactions between mid-latitude trough and subtropical high.Under the effect of southwest flows from low to high levels,there are temperature and dew-point gradients and convergence line on the surface.The dynamic effect of high-level trough and the trigger of convergence line on the surface lead to the convective weather.（2） There are unstable stratifications which are warm and wet in high level and dry and cold in low level.Strong vertical wind shear in the lower troposphere,and the large CAPE and lifting conditions are conducive to occurrence and development of squall lines and super cells.The conditions for the three events are the best on 1 August,better on 11 August and the worst on 7 August.There is a relationship between structure of convective system and the strength of convection forming condition.（3） Monitoring data from radar and dense automatic weather station show that in the initial stage multi-cell echo structures are dominant,and then gradually strengthen and form multi-cell echo groups.In the mature stage,they all develop into linear convective systems and even form organized squall lines.The interaction of updraft and downdraft is the main cause for the development and maintenance of squall lines.（4） The deep warm and moist stratification in the lower and the dry layer above that is important to the forecast of severe convective weather in summer in Henan.The indexes such as CAPE,Δθse（850-500）,ΔT850-500,K index,and vertical wind shear in the lower troposphere have good indication for southwest flow super cell,squall lines and other severe storms to develop and form.