Analysis and Numerical Simulation of Effect of the Mesoscale Southwest Vortex Shear on Rainstorm of Western Guizhou in July 2007

A heavy rainstorm on the large scale occurred in the western Guizhou on 30 July 2007.The feature of cloud cluster and circulation pattern of the heavy rainstorm are analyzed and it is simulated based on MM5 mesoscale numerical model of PSU/NCAR.The physical mechanism of occurrence,development and moving of rainstorm are mainly studied.The result shows that the rainstorm process is not only closely related to mesoscale cloud cluster,southwest vortex and shear and in the midand low-jets,southern trough,but also related to the moving of west Pacific subtropical high.The southwest vortex and shear located from eastern Sichuan to western Chongqing appears on the northwest and the west sides of midand low-jets,and the heavy rainstorm appears the southwest vortex and shear line on the southeast side of junction with the jet.The superposing and coupling of positive vorticity center of upper and low levels in the northwest Guizhou is the main physical mechanism of sustainable development of the southwest vortex and shear,which supplies dynamic support.The vertical ascending motion is the line of the midand low-jets and the southwest vortex.It is also power-driven by southwest vortex.The southwest vortex and shear and the the midand low-jets appear before the rainstorm,and they all move south and then weaken.That means the end of rainstorm in the western Guizhou.