A Study On Short-term Strong Precipitation And Forecast Index In Taiyuan Area

Short-term strong precipitationl has such characteristics as short duration,high intensity,suddenness and small predictability,and accurate forecasting and early warning of it become the key and difficult point of forecasting business.Using the hourly precipitation data in the flood season in Taiyuan from 1970 to 2016,6-hour NCEP reanalysis data,conventional surface and sounding observation data provided by MICAPS and satellite cloud images,short-term torrential rainfall events during the past 47 years have been analyzed in the way of combining synoptic meteorology and statistical methods.Favorable configuration of high an low weather conditions and meteorological environmental conditions for various kinds of short-term torrential precipitation have been researched,and distinguished the different points,and dynamic diagnosis and mesoscale analysis of each classification process have been performed to summary the characteristics of short-term heavy rainfall in Taiyuan na its dynamic,thermodynamic and unstable conditions.The results were as follows:1.According to the situation of low level field's similarity,95 cases have been divided into four categories,namely: I the eastward moving cold vortex pattern,II transversal shear line pattern,III northward moving subtropical high pressure and IV short wave pattern.2.When short-term heavy rainfall occurred,the humidity was increasing with height,and the humidity was not less than 4 g·kg-1 from the ground to 500~550 h Pa.The average surface humidity for Pattern I and IV were about 20 g·kg-1,while Pattern II 15 g·kg-1 and Pattern III 18 g·kg-1.3.The distribution of T-Td was similar to humidity features.Different types of short-time strong precipitation had different convective potential energy,and the average value of CAPE was in the range of 200 ~ 800 J·kg-1.The high energy tongue of K index were distributed in Shanxi besides Pattern III,which indicated the centerof energy accumulation.Taiyuan's K index was between 36 ~ 39 ?,which also provided energy for the occurrence of short-term strong precipitation.4.The positive vorticity distribution was wider for Pattern I and III,while Taiyuan was in the positive vorticity region.The rainstorm area of Pattern I and III occurred in the one degree eastward side by the line of two positive virticity centers.The vorticity distribution for Pattern II and IV was positive and negative alternation,while Taiyuan was in large gradient area of vorticity,and the rainstorm area was located in the 1~2 degree eastward side by the center of positive vorticity.5.The short-term strong precipitation of Pattern III demanded high levels of the whole layer humidity and energy characteristic values,while Pattern II with less humidity.From the point of the energy characteristics,Pattern I required the highest energy,and Pattern IV and II come second,which was closely related to different impact systems.