Cause Analysis of First Heavy Rain over Huaihe Valley during Meiyu Period in 2003
By using physical quantity fields of T213 and objective diagnose analysis system of Beijing University, a synoptic and dynamic analysis of the first heavy rain over Huaihe Valley during Meiyu period in 2003 is made. The low level shear system, which is composed of the southward downdraft branch of upper level northern jet and the ascend branch of low level jet, is the main synoptic system. The vapors mainly come from the Bengal Bay and the South China Sea, but the role of vapors convey from East China Waters shouldn't be ignored. The heavy rain region appears below the positive vorticity center of the mid low level convergence and upper level divergence and near the west side of negative vorticity. And the high value center of the wet potential vorticity coincides with the heavy rain region is instructive to the forecast of heavy rain. The trigger role of frontogenesis by the low level convergence region, vapor supplement and low-level advection is the main reason of the maintenance of heavy rain.