Note on the Rate of Restratification in the Baroclinic Spindown of Fronts

Abstract

This paper revisits how the restratifying buoyancy flux w'b'generated by baroclinic mixed layer instabilities depends on environmental conditions. The frontal spindown is shown to produce buoyancy fluxes that increase significantly beyond the previously proposed and widely used scaling w'b'~fΛ2H2 (f is the Coriolis parameter, Λ is the geostrophic shear, and H is the mixed layer depth), irrespective of whether the initial front is broad or narrow. This increase occurs after the initial phase of the nonlinear evolution, when the baroclinic eddies grow in size and develop velocities significantly in excess of the scaling assumption V ~ ΛH. Implications for parameterizing the restratification caused by baroclinic mixed layer instabilities in coarse-resolution models are discussed. Keywords: Instability; Ocean dynamics; Oceanic mixed layer; Parameterization