摘要
通过数值计算扰动的波谱和谱函数,对垂直非线性切变基流中横波型扰动的不稳定作了数值研究,给出了不稳定谱函数的结构,讨论了不稳定的性质。主要结论有:在基流为非线性垂直切变时,对三支波动连续谱区互不重叠的天气尺度情况,此时出现的不稳定扰动其性质是准地转涡旋波的不稳定,即Rossby波的斜压不稳定。在中α尺度中高端,虽有涡旋波和重力惯性波连续谱区的部分重叠,但这时不稳定的性质仍是涡旋波的不稳定,即准平衡的斜压不稳定。在中α尺度低端,既有准平衡涡旋波的不稳定,又有非平衡的涡旋-重力惯性混合波的不稳定(第一类混合波不稳定)。中β尺度不稳定的性质则是非平衡的涡旋-重力惯性混合波的不稳定,包括第一类混合波不稳定和第二类混合波不稳定。上述情况与线性垂直切变基流的结论相一致,但这里因基流垂直分布较复杂,垂直方向会出现散涡比以1为界的多段交替分布。综上,对于横波型扰动,只要基流不是常数,且层结稳定,虽此时存在纯重力惯性波连续谱区,但均无纯重力惯性波的不稳定,只有涡旋-重力惯性混合波的不稳定。
The characteristics and structures of the instability of adiabatic transversal wave disturbance are studied in this paper by numerical calculation of the wave spectrum and spectral function of the disturbance. It is assumed that the basic flow has nonlinear vertical shear and the stratification and Coriolis parameters are constant. It can be concluded as follows. Whether the basic flow has linear perpendicular shear or not, for the synoptic scale on which the zone of continuous spectrum of three waves do not overlap each other, instability, if it appears, is the quasi-geostrophic instability of pure vortex waves, that is, the baroclinic instability of the Rossby wave. But when the basic flow has nonlinear perpendicular shear, the structure of the instability is more complex. The longwave band of the a mesoscale region has the overlapping part of vortex waves and gravitational inertia waves; it is actually the quasi-balance vortex wave instability, namely the baroclinic instability, and its characteristics and structures are similar to those on the synoptic scale. The shortwave band of the α mesoscale region has both the instability of quasi-balance ageostrophic vortex waves and the instability of mixed vortex-gravitational inertia waves, namely the first class non-equilibrium instability of mixed waves. In the β mesoscale region, if instability exists, it is the non-equilibrium mixed vortexgravitational inertia waves, including the first class and second class instability of mixed waves, that act in accordance with the conclusion of the linear perpendicular shear basic flow. However, because of the complexity of perpendicular distribution of the basic flow, alternative distributions of divergence-vorticity ratios are less than 1 or more than 1, along the perpendicular direction. In sum, for the disturbance of adiabatic transversal waves, if the basic flow is not constant and stratification is stable, there exists an area of continuous spectrum of pure gravitational inertia waves, but not with instability; instability appears only in the mixed vortex-gravitational inertia waves.
出处
《热带气象学报》
CSCD
北大核心
2010年第4期438-444,共7页
Journal of Tropical Meteorology
基金
国家自然科学基金项目(40575023)
青年科学基金项目(40705020)共同资助
关键词
大气动力学
不稳定
谱函数
非线性垂直切变基流
涡旋
重力惯性混合波
dynamics of the atmosphere
instability
spectral function
nonlinear vertical shear
mixed vortex-gravitational inertia waves
