Numerical Simulation and Diagnostic Analysis of a Heavy Rainstorm

With 1°×1° NCEP reanalysis data and AWS rain data,a heavy rainstorm occurred in Rizhao on July 23rd of 2008 was simulated by the meso-scale numerical model(WRF) and diagnostic analysis of the heavy rainstorm are made by using WRF model outputs.The results showed that this heavy rainstorm was affected directly by the Western Pacific Subtropical High(WPSH) when it interacted with westerly trough in addition to the west-south vortex and the shear line of middle and lower layer.Strong transportation and convergence of water vapor resulted in the saturation vapour becoming deeper rapidly,which was helpful for the heavy rainstorm.Moreover,the center of the convergence of water vapor was corresponding to the location of the center of rainstorm.The high-level divergence and low-level convergence were favorable to the convection development and the water vapor transformation from low-level to high-level.Strong ascending motion can provide dynamical condition for the heavy rainfall.The vertical helicity at 700 hPa was closely related with the hourly precipitation.During the heavy rainfall period,a positive vertical helicity column was formed from the low level to top of troposphere,and the appearance of the peak value of precipitation was synchronized with that of the center of positive vertical helicity.