Diagnostic Analysis of Moist Potential Vorticity for Persistant Rainstorm in the Northwest Shandong

Based on the theory of moist potential vorticity,the routine surface observational data and NCEP reanalysis data with the horizontal resolution 1° ×1°,this paper made a diagnostic analysis on a persistant rainstorm in the Northwest of Shandong Province during July 30-August 1,2012.The result showed that the persistant rainstorm mainly resulted from the low vortex at the edge of subtropical high,steady subtropical high and inverted surface trough is the advantage to the rainstorm.The rainstorm occurred in the neighbourhood of the stiff and dense section of the moist isentropes,where the convective stability was so small that it is benificial to SVD.The spatial and temporal variations of moist potential vorticity can give good indication of the development of vortex rainstorm.It is advantage to the development of vortex rainstorm that plus positive zone just over minus one.The rainstorm area is located near the transition zone of positive value and negative value of MPV1 and MPV2 at 850 hPa.