Interactions Between orographically and Thermally Forced Planetary Waves

Abstract

Abstract A comprehensive analysis has been made of the atmospheric planetary wave response to orographic and thermal forcing in midlatitudes using a simple model. Vertical heating profiles with maxima at the surface and in the mid-troposphere are considered. The model is quasi-geostrophic on a beta-plane, and has a constant zonal mean basic-state wind. With these simplifications it is possible to obtain complete analytic solutions, not only for the wave response with and without Ekman pumping, but also for the secondary effects of the waves on the zonal mean flow. The presence of diabatic heating in the waves results in significant non-zero Eliassen-Palm fluxes and violates conditions for non-acceleration of the zonal mean flow, both for propagating and trapped waves. The potential vorticity transport or, alternatively, the Eliassen-Palm flux divergence is shown to be directly related to the vertical heating profile. However, it is the interaction between orographic and thermally forced waves that is main...