高原横切变线上的波动及其与低涡的可能联系

The Waves of the Plateau Transverse Shear Line and Its Possible Connection with the Low Vortex

基于z坐标系下考虑地形的正压模式方程组,利用小参数法求得其一级近似形式,对包含地形坡度与不考虑地形坡度的切变波和涡旋波及其关系进行了理论分析。得出切变线上的波动包括切变波、惯性波和重力外波,属于双向传播的频散波。考虑地形坡度时,波动不稳定条件与波数有关,地形坡度对波动不稳定贡献大小取决于基本气流的纬向分布状况。在不考虑地形坡度时,基流存在南北切变且波长较长时,易出现切变波不稳定。涡旋波不稳定是切变波不稳定的一种特殊形式,即切变线上的波动可通过不稳定发展而形成低涡。理论分析与个例应用表明水平尺度较长的横切变线在一定条件下可诱发低涡生成及东移,从而有利于形成低涡暴雨等极端天气事件。

Based on the barotropic equations regarding terrain in the z coordinate system, obtaining the first-order approximation by using the small parameter method, and then analyzed shear wave and vortex wave and the relationship between them in theory. It was concluded that the wave caused by the wind shear includes the shear wave, the inertial wave and the gravity external wave, which belong to the two-way scattered wave. When considering terrain slope, the necessary condition of wave stability is related to the square of wave number, the contribution of terrain slope to stability fluctuation depends on the zonal distribution of the basic flow. Without considering terrain slope, the basic flow exists north-south shear and the wavelength is longer, there will be wave instability. Vortex wave instability is a special case of shear wave instability, which means the wave of the shear line develops into low vortex through the unstable development of the fluctuation, and shows that the shear line under certain conditions can induce low vortex, which is conducive to the formation of the extreme weather events.