Analysis of a local severe precipitation process on 1 September 2010 in Shanghai against the background of three typhoons’movement

Diagnostic analysis of a local severe precipitation process on 1 September 2010 in Shanghai was made by use of conventional observation data, automatic weather station observations，wind velocity profile data and Doppler radar data at Nanhui of Shanghai. The results indicate that two periods of severe precipitation of this process occurred during active period of the severe tropical storm (1006) Florita, the severe typhoon (1007) Kompasu and the tropical storm (1008) Namtheun. The two periods of severe precipitation were triggered by different synoptic systems. The former was generated by common-effect of westerly trough and typhoon inverted trough, and emerged in the west side of Kompasu, The later occurred at southwest side of Kompasu. It was a severe precipitation generated by the common-action of northwesterly wind at periphery of Kompasu and inverted troughs of Florita and Namtheun, several hours of wind shear and secondary meso-scale convective systems. The interaction between subtropical high and Kompasu made the subtropical high adjusted for a short time. Before turning Kompasu was located at the southwest side of subtropical high, which was favorable for the southeast warm and wet airflow at the west side of subtropical high to stretch to the inland between Shandong and Shanghai to meet the cold air at middle latitudes forming a long distance severe precipitation which is the first period of severe precipitation. After turning of Kompasu, the subtropical high was reinforced and stretched westwards, and its ridge moved southwards cutting off the southeast warm and wet airflow which moved northwards. The southeast warm and wet airflow turned to the area between Shanghai and northern Zhejiang and formed convergence with northwest airflow at periphery of Kompasu, which led to the instable development of atmospheric stratification in Shanghai area triggering the formation and development of meso-scale convection systems and causing the second period of severe precipitation. Analysis of Doppler radar data shows that there are different characteristics about the shape and evolution of radar echoes of rain belts between the two sections of severe precipitation because of different synoptic systems.