Abstract:

According to daily precipitation data from 72 weather stations in the South China area during 2009 to 2013, temporal and spatial characteristics of heavy rainstorms from April to June (pre-summer flooding period) were analyzed by methods of a REOF and a component analysis. The results show that the heavy rainstorm rainfall accounts for 34.6% of total rainfall and the number of annual rainstorm days is over 170 days. By the EOF analysis, the 5 modes of rainstorm area are obtained. Two modes in Guangdong province have higher coefficients than the other modes and have abundant rainfall and stronger rainfall intensity. Using the component analysis, it is found that the rainstorm area in the north of Guangdong province is influenced by westward wind belt system, and mesoscale system of rainstorm is cyclone and deformation field frontogenesis; rainstorm area in the coast of Guangdong province is controlled by subtropical high system, and mesoscale system of rainstorm is low level jet that transfers cyclone shear wind and rotates vorticity to the area and also provide ample moisture from sea surface, so it causes stronger rainstorm in the coast than in the north. There are 14 severe rainstorm (rainfall >200mm) events during pre-summer flooding season in the recent 5 years in Guangdong province, and all of them happened in the coast. Dynamic mechanisms of heavy rainstorm in both areas are different. It is westerlies mesoscale and deformation frontogenesis in the north, while it is subtropical high warm jet system landing and clambering up the coastal land in the coast. SST of off shore provides more latent heat, higher moisture and more active thermal convection environment in the coast than in the north, while sensible heat field show that rainstorm area in the coast could absorb more thermal energy, which is favorable to maintain and strengthen unstable rainstorm process. Analysis of the continue severe rainstorm at Shangchuan island of Guangdong on June 9-12, 2010 suggests that northeast blocking high and subtropical high that extends to west and moves to north both are of similar intensity, so are water vapor flux and convergence of flux divergence. Aslo, barotropic and baroclinic moisture potential vorticity all together are favorable to vertical vorticity development. The above factors are responsible for maintaining the heavy rainstorm process at Shangchuan island of Guangdong province.

Key words: Pre-summer flooding season in the South China, Guangdong rainstorm areas, Synthetic analysis, Heavy rainstorm, Moisture dynamics characteristics