A diagnostic analysis of a rare heavy rainfall process in Jiuquan,Gansu province

Based on data of conventional high-altitude,surface data,intensive surface rain gauge data,,the satellite cloud and 1*1 NCEP reanalysis data every 6 hours,synoptic diagnosis method was used to investigate the characteristics of precipitation which led to a heavy rainstorm process in Jiuquan on June 5,2012,circulation background,including the circulation background,the impact on the system,physical characteristics,and satellite cloud.The results indicated that the heavy rainfall occurred because of the very advantageous large-scale weather situation.The higher levels and lower levels all belonged to high in the east and low in the west with flow field configuration.The presence of a crooked neck ridge resulted in the long time of upstream low value system in western Hexi.Chaidam vortex moved slowly,forming a flow field situation similar to north-trough with south-vortex.The upper-level of the sky diverged and the low-level converged when rainfall occurred,producing a strongly suction effect;the strongly upper motion in the troposphere and the configuration in low-level flow field were beneficial to the transport and aggregation of vapor.Heavy rainfall always happened in the combined area with convection instability and baroclinic instability and the downstream or the moving front of the center of CAPE.During the rainfall,there were several mesoscale cloud clusters on the upper sky of Jiuquan,indicating that mesoscale and small scale convective systems obviously existed.