中尺度西南涡、切变线对“07.7”贵州西部暴雨影响的分析与模拟

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

2007年7月30日贵州西部出现了大范围的强暴雨过程,本文分析了这次暴雨过程的云团特征和环流形势,并利用PSU/NCAR的MM5中尺度数值模式对这次暴雨过程进行了数值模拟,重点研究这次暴雨发生、发展和移向的物理机制。结果表明:这次暴雨过程与中尺度云团、中低层西南涡、切变线、南支槽和中低空急流活动密切相关,同时还与西太平洋副热带高压活动相关。位于四川东部至重庆西部的西南涡、切变线出现在中低空急流的西北侧或西侧,而贵州西部强降水发生在西南涡、切变线南侧与急流交汇处。高、低空正涡度中心在贵州西北部地区上空的叠加、耦合是该西南涡、切变线持续发展的主要物理机制,为暴雨的发生提供动力条件。垂直上升运动是中低空急流和西南涡联系的纽带,也是西南涡动力驱动的结果。西南涡、切变线和中低空急流在暴雨出现前建立,而暴雨、中低空急流和西南涡、切变线几乎同时南移减弱,预示贵州西部暴雨即将结束。

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.