A numerical study on saturation mechanism of gravity wave in mesosphere

Saturation mechanism of gravity waves in mesosphere is discussed by simulat ing the nonlinear upward propagation of gravity wave in mesosphere. The sim ulation results show that: the amplitude of an upward propagating gravity-w ave packet will increase with the increasing height until the horizontal di sturbance 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 conseq uence of overgurning, and breakdown is occurs as a consequence of small-sca le convection, while turbulence is only an end product of the wave saturati on. Though wave breakdown, turbulence and wave-mean flow interaction can re duce the wave-associated energy, all these physical processes play secondar y roles in limiting wave growth during the nonlinear propagation, the domin ant mechanism of wave saturation is overturning.