The effect of the Benthic Boundary Layer on the physics of intense mesoscale eddies

It is found that the decay of eddy-like flow occurs through conversion of kinetic to potential energy and through dissipation by bottom friction. The relative importance of both processes is expressed by the Rossby number and by the stratification parameter. A larger Rossby number and stratification parameter lead to a larger conversion of kinetic to potential energy, but a smaller mechanical dissipation of the same energy. Examination of the structure of the Benthic Boundary Layer indicates that a clear distinction should be made between the mixed layer, or the region neutrally stratified, and the Bottom Boundary Layer, or the region where most of the turbulent activity occurs. It is found that the structure of the Bottom Boundary Layer depends also on the magnitude of the flow above the Benthic region, but the mixed layer depends also on the sign of the mesoscale activity. Under a cyclonic flow, the mixed layer is defined by vertical advection and it is usually much thicker than the Bottom Boundary Layer. The mixed layer of an anticyclonic flow is the result of both vertical advection and near bottom turbulence, and the ambiguity between the mixed layer and Bottom Boundary Layer is notably reduced.