The Linear Response of a Hemispheric Two–Level Primitive Equation Model to Forcing by Topography

Abstract

A hemispheric solution is obtained for the topographically forced stationary linear perturbations in a two-layer primitive equation model of the atmosphere. Results are discussed for January conditions. Additionally, the linear theory of stationary perturbations in a quasi-geostrophic two-layer model with ?-plane approximation is presented which shows that three types of standing waves may be excited by the topography. The structure of these waves and the conditions under which they appear are discussed. Furthermore, the influence of the surface friction and the vertical shear stress on these waves is studied. This quasi-geostrophic theory is applied to the January case. It turns out that the topography induces so-called ultralong waves without a horizontal node in the frictionless model atmosphere. Cold troughs develop at both levels over the major mountain chains such as the Himalayas and the Rocky Mountains. The standing waves in northern latitudes seem to be forced by the orography in middle and southern latitudes. The incorporation of surface friction and vertical shear stress into the model causes a strong eastward displacement of the standing waves and weak transports of heat and momentum.