Numerical Simulation And Diagnostic Analysis Of A Low Vortex Heavy Rain In Shanxi Province

Based on conventional surface observations and radiosonde soundings and NCEPreanalysis data (spatial precision 1°×1°), by analyzing the synoptic situation and thephysics quantity fields of the low vortex heavy rain process occurred on 1-2 July2005 in Shanxi Provence. It is found that the heavy rainfall occurred in a wellweather situation with the high-level trough and subtropical high at 500hPa andmeso-scale low vortex. Moreover, It is also revealed that in the vicinity of heavy rain,the diagnostic fields such as vorticity and divergence at low levels was coordinatedto that at high levels of atmosphere, contributing to the sustaining strong updraft, oneof the favorable conditions for occurrence and persistence of the rain.The mesoscale numerical model WRF (V2.1.2) are used to simulate this processsuccessfully, Using the model output with high spatial and temporal resolution, westudy the characteristic and mechanism of the rainfall in more detail. It is found themain weather system brought the heavy rain was a mesoscale vortex at low-midlevels,whose evolution was accorded with the variations in shift and intensity of therainfall center, relations between removal entropy index and rainfall area areanalyzed, The results are as follows: the evolution of remove entropy index fromhigh to low advantage the developing of convection and lead to the heavy rainfallformation; The negative entropy change (REI＜0) corresponds with the large-scaleheavy rain, the rainfall scale is represented by the convergence of the negativeentropy change;The removal entropy index match the heavy rainfall centers quitewell. The diagnosis of moist potential vorticity (mpv) shows that there are theinstability area of MPV＜0, and the negative focus of MPV located at the focusof heavy rainfall Above the rainfall area, when heavy rainfall happening.Moreover,MPV1＜0, MPV2＞0 and |MPV1≥MPV2|are the favorable environment of heavyrainfall generating, finally, Sensitivity experiments further reveal the amplifyingeffect of terrain on the heavy rain.