Wet Rotation Analysis of Southwest Vortex Causing a Heavy Rain in Southern Sichuan Basin

Based on the 6-hour-interval reanalysis data with 1.0°×1.0°resolution from NCEP/ NCAR,station observational data and so on,a heavy rainfall during July 2009 are analyzed.The results show that the southwest vortex on 850hPa is more obvious,the heavy precipitation is to the southwest of the southwest vortex,and the heavy precipitation field has a good relation to the strong ascending motion.The heavy precipitation is in the negative field of moisture potential vorticity,the vertical component of wet vorticity could show the combined effect of atmospheric rotation and water vapour transport.It also has a good correspondence with rainfall and provides a new way for determining the variations of rainfall.