Analysis of a Heavy Rainstorm in Central-northern Shaanxi Province

In this study,a heavy rainstorm that occurred in central-northern Shaanxi Province on August 28,2006 was comprehensively analyzed using routine meteorological data,FNL reanalysis and FY-2C satellite nephograms.The results revealed that the confrontation of the subtropical anticyclone extending westward and the cold air mass coming from the Lake Baikal provided favorable vast-scale conditions for formation of a heavy rainstorm.A low-vortex shear,low-altitude jet flow and surface cold front were the primary factors affecting the heavy rainstorm.In addition,the vapor channel of this rainstorm originated in the South China Sea,extended along the airflow around the subtropical anticyclone,and arrived over the rainstorm area,which resulted in a congregation center of vapor flux at a mid-low altitude.A mid-altitude dry-cold air mass coming from the north invaded the warm air mass,and an unstable convection formed over the rainstorm area.Vertical distribution of vorticity,divergence,velocity and other physical quantities led to formation of the rainstorm and the divergence was then vertically distributed in a multilayer fashion.The heavy rainstorm occurred over the warm area of the surface cold front,there were four meso-β scale convective systems that affected the rainstorm area,and the meso-β scale convective systems had a direct effect on the heavy rainstorm.