两次高原切变线诱发低涡活动的个例分析

Case Analysis on Two Low Vortexes Induced by Tibetan Plateau Shear Line

使用NCEP/NCAR再分析格点资料,对2007年7月4～6日切变线在高原上发展,并诱发两次高原低涡造成高原中部大雨的活动过程进行了诊断分析。通过涡度收支等物理量计算,结果表明,垂直输送项和水平辐合辐散项对两次高原低涡的发展增强都起主要作用,在低涡不同发展阶段,二者贡献各有不同;在低涡二消亡阶段,水平平流项贡献增大。视热源和视水汽汇分析表明,这次降水过程以对流性降水为主,垂直运动的负值中心与视热源、视水汽汇中心对应,变化趋势基本一致,表明在降水过程大气加热是与大气上升运动密切相关,对流层中层的加热引起对流层低层抽吸作用会促进高原涡的发展,大气热源主要是降水过程的凝结潜热释放,水汽凝结起决定性作用。

Using the NCEP/NCAR reanalysis data, the shear line over the Tibetan Plateau（hereafter Plateau） from 4 to 6 July 2007 are diagnostically analyzed, and two low vortexes induced by the shear line which cause moderate rain in central Plateau, the results show that the perpendicular transportation term and the horizontal divergence and convergence terms have played a major role in the development of the two vortex, in the different stages of the development of vortex, which have different contributions. At the same time, the contribution of horizontal advection has increased during the extinction phase. The results of apparent heat source and apparent moist sink suggest that the process of precipitation in convective precipitation, the negative center of vertical movement is corresponding to apparent heat source and apparent moist sinkrs, having same change trend, indicating that atmospheric heating is closely related to ascending motion during process of precipitation, the heating in middle troposphere causes pumping action in lower troposphere which can promote the development of plateau vortex, the condensation latent heat releasing is main heat source, moisture condensation plays a decisive role.