Diagnostic analysis of moist potential vorticity for a rainstorm in North China

Based on the conventional ground observational data and regional intensive precipitation data from weather station as well as the NCEP reanalysis data(horizontal resolution with 1°×1°,time interval with 6 h),moist potential vorticity(MPV) of a rainstorm process on June 8,2009 in North China was analyzed.The results indicate that the distribution characteristics of MPV are indicative of occurrence and falling area of rainstorm.The vertical overlapping of the positive and negative MPV1 areas is favorable to the generation and development of rainstorm.The rainstorm area is located near the transition zone of positive value and negative value of MPV,MPV1 and MPV2 at 850 hPa.This zone is also the conjoint area of convective instability and baroclinic instability.The region in which isentropes of θse is nearly linear is favorable to the increase of vertical vorticity and occurrence of rainstorm.