Abstract:

 Based on the observed meteorological data and the NCEP reanalysis data (2.5°×2.5°), the synoptic background, dynamical conditions, thermodynamic and water vapor conditions of three heavy rainstorms on July 9, 1991, July 21, 1998 and July 8, 2010 during the Meiyu period in Hubei province were analyzed in order to forecast accurately the similar regional rainstorm. The results show that the locations of upper and lower jet streams and the path of water vapor transport are similar for these three rainstorms. The meso-scale system affecting the three processes is the southwest vortex-shear line. The locations of the positive vorticity center at 850 hPa and water vapor flux convergent center are coincident well with the falling area of rainstorm, which indicates that the low-level wind convergence and vertical ascending motion are favorable to the heavy rain. The sum of the absolute values of moist potential vorticity (MPV) barotropic and baroclinic conditions at 700 hPa in the rainstorm area is about 0.5-0.6 PVU during the three rainstorm periods, and the humidity saturation zone of the three rainstorms are extended above 500 hPa. The locations of the southwest vortex-shear line and low-level jet stream are important factors for forecasting the falling area of rainstorm. In addition, the low-level vortex, water vapor flux divergence, high energy tongue of the pseudo-equivalent temperature and atmospheric vertical structure could provide references for forecasting the falling area of rainstorm.

Key words: Meiyu period, Rainstorm, Jet stream, Moist potential vorticity