天津一次局地大暴雨中尺度对流系统组织化特征与成因

Organization characteristic and causal analysis of meso-scale convective system of locally torrential rain in Tianjin

应用常规观测资料与地面加密自动站、卫星云图、多普勒雷达等多种非常规观测资料以及雷达变分同化分析系统(VDRAS)分析场资料,对2013年7月1日天津南部大暴雨中尺度对流系统的结构、演变特征及其成因进行了分析。结果表明:(1)大暴雨发生在副热带高压边缘暖湿气流、低空700—850 h Pa暖性切变线、高低空急流有利配置的背景下,属暖区暴雨。(2)大暴雨由若干β中尺度对流云团合并加强后的α中尺度对流云团造成,对应雷达,强降雨是由西南方向不断移入天津南部的γ中尺度对流单体发展加强,并先后组织成若干东—西向带状β中尺度对流系统先东北后偏东方向移动造成的,在大港南部有列车效应,具有典型的热带型降水回波特征。(3)逆风区的出现、中空急流向低层伸展,低空急流、超低空急流先后形成并加强,是降水强度加强的重要原因。(4)地面中尺度切变线的维持、加强和中尺度低压倒槽东移、发展、入海加强为中尺度气旋,是先后造成对流单体发展加强并组织成带状中尺度对流系统的两个中尺度系统。(5)近地层中尺度切变线是地面中尺度切变线形成的原因,对流单体前侧的偏南冷性水平出流的叠加,一方面增强了沿切变线的辐合,一方面也加大了低层的水汽输送;带状对流系统后侧的偏北冷性水平出流与东南气流形成的中尺度切变线是地面中尺度气旋形成的原因。

Using data from conventional observations, automatic weather stations, satellite, Doppler radar, and variational Doppler radar anal- ysis system （VDRAS）, the structure and evolution characteristic of meso-scale convective system occurred in south of Tianjin on July 1,2013 was analysed. The results indicate that： 1） The torrential rain belongs to the warm area rainstorm, which occurred in favorable conditions of warm air on the edge of subtropical high with warm shear line at 850-700 hPa. 2） The strong rainfall was formed in process of meso-β scale convective cloud clusters moving from the southwest to northeast, constantly merging and strengthening, forming oval-shaped and then band meso-α convective clouds. Meso-γ scale convective echo was suddenly strengthened in southern Tianjin, forming some east-west meso-β scale band echo and then moving to the east and northeast. The train effect was happened in southeast area of Dagang, with the typical characteristics of tropical precipitation echo. 3） The factors of adverse wind area, middle-level jet stream stretching to low-level, low-level and super low-level jet forming and strengthening were the important causes of precipitation intensification.4）The sustained meso-scale sur- face shear line and the meso-scale depression trough moving to the east and strengthening to meso-scale cyclone were two meso-scale sys- tems leading the convective cell to develop and then form band meso-13 convective system. 5） The wind shear near the ground was the cause of surface wind shear forming. The south outflow in front of convective cell strengthened the convergence along the shear line, and was in favor of the water transportation. The convergence of the north outflow behind the band convective system and southeast flow formed the meso-sclae shear line, which was the cause of the formation of surface meso-scale cyclone.