Investigation of an Extremely Heavy Rainstorm Event over the Southern Seacoast of Shandong Peninsula

An extremely heavy rainstorm event in Jiaonan area of Shandong Province were occurred on21 September,2012.The precipitation reached to 394.1mm within about 13 h.This extremely heavy rainstorm event was not in the range of traditional heavy rainfall weather system,because there was no typical evidence at high and low levels.In this paper,the observational data of automatic weather stations,radar data and 0.25°× 0.25°ECMWF(European Centre for Medium-Range Weather Forecasts)reanalysis data were used to investigate the various factors which triggered this rainstorm event.The result indicated that this weather system was not so deep,but at low-level the water vapor converged significantly.Atmospheric stratification appeared asstable-unstable-stable-unstablesituation from high level to low level.The dynamic tropopause which was characterized by potential vorticity folded apparently.Perhaps the condensation occurred due to the mixing of dry cold air from high level and the moist warm air from low level was the main reason of generating the heavy rainstorm event.The two components of MPV(Moist Potential Vorticity,MPV1 and MPV2)changed significantly before the rainfall.MPV2 at low levels could be regarded as a good tracer for rainfall area.There was a strong eastward vorticity advection in the isentropic surfaces at middle and low levels.Wind direction was almost vertical with the isoline of potential vorticity.It was showed that the rainstorm system moved quickly.