Study Of Summer Short-duration Heavy Precipitation And Thresholds Of Key Physical Variables In Shanxi Province

Based on daily precipitation data at 1727 observation stations in Shanxi province during the summer from 2013 to 2015,typical short-duration heavy precipitation events were picked out.With the aid of conventional meteorological observation data and Doppler weather radar,satellite,microwave radiometer fine detection data,a climatology of short duration heavy rainfall was studied and the main types of synoptic system were summarized.The 12 physical parameters or factors and their thresholds were defined and a forecast model was proposed for the equation of correlation coefficients between the heavy precipitation and the parameters or factors.By using the observations in the flood season of 2016,the model was assessed.The main conclusion is as follow:The averaged number of more than 20 mm/h heavy rainfall events is 1076.9 every year and the heavy precipitation of ?50 mm/h has an obvious interannual variability.The short-duration heavy rainfall events happen more in July and less in September,and occur most in the region surrounding Taiyuan and southeast region of Changzhi and Jincheng.The heavy rainfall events have an obvious diurnal variation with low frequency during 00:00~05:00 am,high around 7:00 am,10:00 am,15:00 pm and 17:00 pm,and peak frequency around 10:00 am.The synoptic weather system having an impact on the short-duration heavy precipitation includes the low vortex groove type,the westerly trough(plateau)type,the subtropical high type,the typhoon indirect effects type,the westerly trough type/cold eddy and subtropical high type.The statistics results show that 16 physical parameters may contain some information for the heavy precipitation forecasting,i.e.depression of the dew point,K indices,SI index,CAPE(the convective available potential energy),depth of moisture layer,the lift condensation height,vertical wind shear(0-6km),?se,Sweat index,the minimum value of cloud-top brightness temperature,the strong echo center value,gradient of GPS vapor.The membership function is used to transform the16 parameters,and then a forecast model is established.Forecast verification shows that the model has some prediction skill during a summer forecasting experiment in 2016.