Analysis of a Torrential Rain Process in the Autumn of 2011 in Guangdong and its Characteristics of Water Vapor

Observations and NCEP reanalysis gridpoint data were used to study a torrential rain that took place across the province of Guangdong on October 12—14,2011. The results are shown as follows.( 1)This process can be divided into two stages,one being a warm-sector torrential rain on the night of October12 and the other being a frontal one on the night of October 13.( 2) The precipitation of Stage one is mainly caused by a westerly shortwave trough at 500 hPa associated with a southeasterly convergence at 850 hPa while that of Stage two results from the passage of a westerly trough at upper levels in association with the south-going surface cold air and a low-level shear.( 3) The water vapor is so rich in the province prior to the precipitation that a wet layer grows all the way upwards in large depth and about 50% of the amount of precipitation is supplied by local sources of water vapor.( 4) The southeasterly wind at the lower level of 850 or925 hPa is an important channel of transporting water vapor and the active tropical systems over the South China Sea prior to the torrential rain are greatly responsible for the southeasterly wind being transported constantly.