Diagnostic analysis on Meiyu rainstorm and its simulation based on backward trajectory analysis method during June 2009 in the south of Anhui province

Based on the conventional observation data, the NCEP (2.5°×2.5°) reanalysis data and the GBL data from NOAA, a heavy rainstorm process on June 28-30, 2009 in the south of Anhui province was analyzed. Water vapor source was simulated by backward trajectory analysis method (Hysplit_4 dispersion model). The results indicate that divergence in upper level and convergence in lower level exist simultaneously, which leads to lifting motion. It becomes the dynamic conditions of this rainstorm. The adequate water vapor sources from the Bay of Bengal and the South China Sea are the premise conditions of forming rainstorm. At the same time, the convergence in lower level comes into being shear line, which makes the high instability energy released. These conditions accelerate the forming of rainstorm.