On steady quasi-geostrophic flow component formation over undulating bottom topography .2. A two-layer low-order model of the open ocean

An equilibrium quasi-linear regime consisting of forced topographic waves and a steady flow component correlated with bottom relief is analysed using the low-order spectral model of quasi-geostrophic ocean dynamics. Two functions - a correlation C between potential vorticity and the topography and a topographic stress force D - are employed to study the qualitative structure of the steady flow component. Both a negative and positive C appear in the model. This function is defined mostly by topographically induced energy fluxes among barotropic and/or among baroclinic modes when the horizontal scale of the bottom undulations is smaller than the internal Rossbi radius. Over the large-scale topographic features, the interface displacements, controlled by the energy transfer between barotropic and baroclinic components, dominate in C. The beta-effect tries to develop negative homogeneous C. D is derected oppositively to the phase velocity of the incident wave for motions on anf-plane. The beta-effect induces a westward mean zonal component of D when a barotropic flow component is directly forced or in the case of a wind-stress forcing. When a baroclinic wave is derectly forced, both negative (over a small-scale topography) and positive (over a large-scale topography) zonal components of D may appear. The analysis of the vertical structure of the steady flow component, and the linear stability analysis of the equilibrium dynamical regime are fulfilled.