Analysis of Generalized Wet Potential Vorticity in Two Extreme Rainstorms in the Western Sichuan Basin

Based on the 0.25°×0.25° reanalysis data from ERA5, the conventional data from MICAPS4 and the hourly precipitation observation data from the Sichuan Automatic Stations, the generalized potential temperature( \theta ^* ) and generalized wet potential vorticity(GMPV) of the two extreme rainstorm processes occurred in the western Sichuan Basin on 11~13 and 15~18 August 2020 were diagnosed and analyzed. The results indicate that: The two rainstorm were ‘east high and west low’ in the 500hPa. The South Asia high pressure, high altitude jet, west wind trough, low-level shear line and vortex were favorable dynamic conditions for the two rainstorms. Low-level jet was a good water vapor condition in rainstorm area. There were \theta ^* gradient area and GMPV anomaly area over the two rainstorm areas, the warning height of '8.11' was 800~900hPa, and the height of '8.15' was 700~800hPa. This distribution was closely related to the low-level relative humidity(rh) content, that is, the higher the rh, the stronger the vertical gradient of \theta ^* and value of the abnormal area of GMPV. The temporal and spatial evolution of \theta ^* and GMPV had a good correspondence with the temporal evolution of heavy precipitation stations. However, there was no significant positive correlation between the GMPV intensity and hourly rainfall intensity.