Analysis of Synoptic Cause of a Heavy Rainfall Event in Autumn

Based on the conventional meteorological data and WSR-98D radar data of Jinan, Shandong province, the upper air circulation, physics diagnostic field, the evolution of hourly precipitation with time, the base velocity and composite reflectivity, and so on are analyzed. The conclusions are as follows:(1) The stable upper air circulation at 500 hPa is the essential factor. (2) The convergence of vapor flux in the boundary layer is the source of water vapor. (3) The strong ascending motion is caused by “pumping” which is formed by strong convergence occurs in the north of the meso-scale cyclone and upper air divergence at high levels, (4) The meeting of two low-level jets makes the first hourly precipitation peak and the development intensively of meso-scale cyclone which makes the other hourly precipitation peak of Cangzhou station.

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