中层大气中重力波饱和机制的数值分析

通过对向上传播的重力波波包在中层大气中的非线性传播过程进行数值模拟,讨论中层大气中重力波的饱和机制.数值模拟结果表明,向上传播的重力波波包的扰动振幅在接近波包的本征水平相速度之前随高度单调增长,而当波振幅接近本征水平相速度时,在对流不稳定区域出现等位温面的翻转,同时波振幅的增长达到饱和（波振幅随高度不发生变化）.小尺度对流在等位温面的翻转和波饱和发生后产生,随后波包开始破碎,这些非线性过程的最终结果产生湍流.表明导致重力波饱和的关键因素是等位温面的翻转而不是诸如波破碎、湍流、波-流相互作用等其他的一些物理过程.

A NUMERICAL STUDY ON SATURATION MECHANISM OF GRAVITY WAVE IN MESOSPHERE

Saturation mechanism of gravity waves in mesosphere is discussed by simulating the nonlinear upward propagation of gravity wave in mesosphere. The simulation results show that:the amplitude of an upward propagating gravity wave packet will increase with the increasing height until the horizontal disturbance velocity is close to the horizontal intrinsic phase velocity. At the same time,the overturning occurs in a limited unstable region and then the wave is saturated. Small scale conection appears as an immediate consequence of overgurning,and breakdown is occurs as a consequence of small scale convection,while turbulence is only an end product of the wave saturation. Though wave breakdown,turbulence and wave mean flow interaction can reduce the wave associated energy,all these physical processes play secondary roles in limiting wave growth during the nonlinear propagation,the dominant mechanism of wave saturation is overturning.