General Properties of Baroclinic Modons over Topography

Abstract

The properties of solitary topographic Rossby waves (modons) in a uniformly rotating two-layer ocean over a constant slope are analyzed. The modon is described by exact, form preserving, uniformly translating, horizontally localized, nonlinear solution to the inviscid quasigeostrophic equations. Baroclinic modons over topography are found to translate steadily along contours of constant depth in both directions: either with negative speed (within the range of the phase velocities of linear topographic waves) or with positive speed (outside the range of the phase velocities of linear topographic waves). The lack of resonant wave radiation in the first case is due to the orthogonality of the flow field in the modon exterior to the linear topographic wave field propagating with the modon translation speed that is impossible for barotropic modons. Another important property of a baroclinic topographic modon is that its integral angular momentum must be zero only in the bottom layer; the total angular momentum can be non-zero unlike for the beta-plane modons over flat bottom. This feature allows for modon solutions superimposed by intense monopolar vortices in the surface layer to exist.