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

Using conventional observation data, automatic weather stations data, Satellite data, Doppler radar data, and variational Doppler radar analysis system(VDRAS) data, the structure and evolution characteristic of meso-scale convective system 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, warm shear line at 850-700hPa. 2) The strong rainfall was formed in process of meso-β scale convective cloud cluster which from the southwest moving to northeast, constantly merging and strengthening, forming the oval and then band meso-α convective cloud. 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 adverse wind area, middle-level Jet stream strentching to low-level,low-level and super low-level jet forming and strengening, was the important cause of precipitation strengened .4)The maintenance of meso-scale surface shear line, the meso-scale depression trough moving to the east and strengening to meso-scale cyclone, was two meso-scale system which leading the convective cell developing and then forming band meso-β convective system.5)The wind shear near the ground was the cause of suface wind shear forming, the south outflow in front of convective cell was strengening 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 was forming the meso-sclae shear line, which was the cause of the forming of surface meso-scale cyclone.