Nonlinear studies on the effects of topography on baroclinic zonal flows

We examine the generation of transient and stationary waves when baroclinic solid body rotation zonal currents flow over topography within an inviscid two-level nonlinear quasi-geostrophic model on a sphere. The equilibrium climate states resulting from different initial conditions are obtained for wide parameter ranges. The climates are obtained, not by direct integration and taking long time averages, but instead by using methods of equilibrium statistical mechanics. The effects of topography depend strongly on where, in the (U 1 , U 3) phase space of solid body rotation components, the initial flow lies. Five regions of this phase space R 1 , R 2 , RT, RB1 and RB3 have been identified. For (U 1 , U 3)εR 1εR 2 the flow is little disturbed by the topography h and is nonlinearly stable as h≡0. In the region RT , the flow would be stable if h ≡ 0. However, even in the limit h≡0, large amplitude transients are generated through topographic instability. In the regions RB1 and RB3 large amplitude transients are generated for finite h, as h≡0 and with h≡ 0 due to baroclinic instability. The numerical studies indicate the remarkable result that irrespective of the initial solid body rotation components, their climate values (⟨U 1⟩, ⟨U 3⟩)εR 1εR 2 at least as h≡0.