Artificial Retardation of Barotropic Waves in Layered Ocean Models

Abstract

The effect of reducing the barotropic gravity wave speed in a layered ocean model in order to gain computational speed is explored. In theory the error in the propagation of baroclinic gravity waves typically is less than 3% for a reduction of the external gravity speed by one order of magnitude. This is confirmed in a numerical experiment. For baroclinic Rossby waves, the phase speed error is even less. The barotropic response is limited to the reduced radius of deformation. The method, which we will refer to as gravity wave retardation, is therefore applicable only for oceanic flows where the barotropic mode is of minor importance. It is demonstrated that the method gives very good results for the baroclinic flow of an equatorial jet, spinup of a midlatitude ocean and flow over a midoceanic ridge. The method can be considered as an alternative to multilayer reduced gravity models, and has the advantage that bottom topography can be included.