Suppression of Stationary Planetary Waves by Internal Gravity Waves in the Mesosphere

Abstract

The suppression of stationary planetary waves by internal gravity waves in the mesosphere is treated using a quasi-geostrophic model on a midlatitude beta-plane. The drag forces due to internal gravity waves are parameterized based on the wave breaking assumption recently proposed by Lindzen. In the present model the vertical propagation of internal gravity waves is affected not only by mean zonal wind distribution but also by eastward and northward velocity perturbations associated with stationary planetary waves, viz., the total local velocity. Numerical mulls show that the drag force due to breaking internal gravity waves acts like a Rayleigh friction, and the amplitudes of stationary planetary waves in the mesosphere are much reduced by this effect. Equivalent Rayleigh friction coefficients are also presented.