The application of second order potential vorticity in the forecast of rainstorm

The second order potential vorticity was introduced and derived in this paper. Using NCEP/NCAR 0.5°× 0.5°GFS 24 h forecastdata, the vertical integration of the absolute value of the second order potential vorticity from 500 hPa to 850 hPa was calculated for rainstormsassociated northeast cold vortices, fronts, cold shear lines and typhoons. The calculated results were compared with the corresponding observed24 h accumulative ground precipitation. The results show that the second order potential vorticity and the precipitation areas are closelyrelated, and the second order potential vorticity is a good indicator to forecast precipitation. The ETS grades were further calculated for caseswith 6 h accumulative precipitation higher than 10 mm in the 24 h forecast in south-China area (20°-35°N, 105°-125°E) from June to Augustin 2013. which shows that the second order potential vorticity is a good forecast utility to the observed precipitation.