Diagnostic Analyses of an Abrupt Torrential Rain at Jianghan Plain

An abrupt torrential rain occurred at the south of Jianghan Plain at the night of 24th May* 2006.Using NCEP analyzed data and automatic meteorological station data* a research is conducted.The results are reached as follows: before the heavy rain* the south border of upper level jet(ULJ) stream retreated from Hubei province to the north* with the occurring and weakening of the rain* the border came back to the upper level over Hubei province again;before the heavy rain* the core of the ULJ moved from the west to the east within the zone from 35°~40°N* and when the heavy rain began* it was at the northeast of Hubei province already.The occurrence of the torrential rain coincided with the strengthening of a meso-scale zone with positive vorticity at boundary layer;water vapor was transported from northwestern South China Sea to Central China at low levels;during the rain there were decrease of inertial stability at high level and maintaining of potential instability at low levels;before the heavy rain* large positive moisture helicity divergence appeared at 950 hPa level.