Moist Helicity Analysis of a Heavy Rainstorm in Sichuan Basin Induced by Plateau Vortex Moving Eastward

Using NCEP 1°×1° reanalysis data and the different height data of conventional observation,a case of heavy rainstrom in Sichuan basin caused by plateau vortex moving eastward from 30 to 31 July 2009 was analyzed by both the synoptic and dynamic methods,including the moving of the plateau vortex,distribution of rainfall,transportations of water vapor and helicity.The results showed that distribution of 500 hPa moisture helicity can give good indicator to the distribution and center of rainfall,the moisture helicity increased in the period of severe precipitation.The moisture helicity can reflect the dynamic character of weather when the rainstorm occurs,and divergence of negative vorticity on upper level cooperated with convergence of positive vorticity and vapor rotate rising on lower leve1 is a dynamic mechanism to trigger rainstorm,which has a better positive correlation with precipitation area and distribution in the next 6 h.The severe precipitation center generally appears on the side of maximum gradient value of relative spiral.The results have a certain reference value to the forecast of precipitation area and intensity distribution.