Formation Mechanism of a Low Vortex Heavy Rain in Shanxi Province

Based on the conventional surface observations and the NCEP reanalysis data(spatial precision 1°×1°),the synoptic situation and the physics quantity fields of the low vortex heavy rain process occurred on 1-2 July 2005 in Shanxi Provence are analyzed.The heavy rainfall occurred in a well weather situation with the high-level trough,the subtropical high at 500 hPa and the meso-scale low vortex.Using the model output with the high spatial and the temporal resolution,we study the characteristics and formation mechanism of the rainfall in more detail.It is found that the main weather system brought the heavy rain is a meso-scale vortex at low-mid levels,whose evolution is accorded with the variations in shift and intensity of the rainfall center.The diagnosis of moist potential vorticity(MPV) shows that the negative MPV area is instability,and its center located at the center of heavy rainfall.when heavy rainfall happening.Moreover,|MPV1|≥|MPV2| are the favorable condition for the heavy rainfall generating.Moreover,the sensitivity experiments further reveal the impact of terrain on the heavy rain.