Diagnostic analysis of a southwest vortex producing heavy rainfall in Guangxi Province in June 2008

Based on NCEP 1° ×1° re-analysis data,hourly precipitation data and LAPS 0. 045° ×0. 045° re-analysis data,a severe heavy rain event that occurred in Guangxi Province at 20: 00 on June 11,2008 to 20: 00 on the 13th was analyzed. The high and low level jet,the southwest vortex and the shear line extending from the vortex center were the main systems of the rainfall. The heavy rain event mainly occurred in the right-rear area of the high-level jet,on the left side of the low-level jet,at the bottom to the rear of the vortex and near the shear line. The heavy rainfall center moved toward the east with the eastward shifting of the systems. Precipitation increased with the strengthening of the southwest vortex. During the heavy rainfall the southwest vortex had the warm core at 700 hPa. The positive vorticity region extended vertically upward,and the entire troposphere took on positive vorticity. The lower-level convergence and upper-level divergence were favorable for the development of convection. The upward motion was strong over the strong precipitation center. In the vorticity budget equation,the horizontal vorticity advection was playing a role opposite to the horizontal vorticity diversion which had the direct function and made positive contributions in the total vorticity field in the lower troposphere. The vertical advection and the twisting term played the main role in the middle and upper troposphere.