A ray tracing model of gravity wave propagation and breakdown in the middle atmosphere

Abstract

Gravity wave ray tracing and wave packet theory is used to parameterize wave breaking in the mesosphere. Rays are tracked by solving the group velocity equations, and the interaction with the basic state is determined by considering the evolution of the packet wave action density. The ray tracing approach has a number of advantages over the steady state parameterization of Lindzen (1981), as the effects of gravity wave focusing and refraction, local dissipation, and wave response to rapid changes in the mean flow are more realistically considered; however, if steady state conditions prevail, the method gives identical results to Lindzen (1981). The ray tracing algorithm is tested by using both interactive and noninteractive models of the basic state. In the interactive model, gravity wave interaction with the polar night jet on a β plane is considered. The algorithm produces realistic polar night jet closure for weak topographic forcing of gravity waves. Planetary‐scale waves forced by local transfer of wave action into the basic flow in turn transfer their wave action into the zonal mean flow. Highly refracted rays are also found not to contribute greatly to the climatology of the mesosphere, as their wave action is severely reduced by dissipation during their lateral travel.