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. [