Roles of Shear and Convection in Driving Mixing in the Ocean.

Using field, numerical, and laboratory studies, we consider the roles of both shear and convection in driving mixing in the interior of the density‐stratified ocean. Shear mixing dominates when the Richardson number Ri < 0.25, convective mixing dominates when Ri > 1.0, and in the intermediate regime when 0.25 < Ri < 1.0 both shear and convection can contribute to mixing. For pure shear mixing the mixing efficiency Rif approaches 0.5, while for pure convective mixing the mixing efficiency Rif approaches 0.75. The diapycnal diffusivities for the two mechanisms are given by very different expressions. Despite these complexities, a simple mixing length model using the mean flow shear S provides robust estimates of diffusivity across the range 0 < Ri < 2. To account for the roles of both shear and convection over this range of Ri, we also formulate a modified version of the empirical KPP model for parameterizing ocean mixing in numerical models. Key Points: When Ri < 0.25 shear dominates ocean mixing whereas when Ri > 1.0 convective mixing dominatesIn the ocean, the maximum Rif for shear mixing approaches 0.5, while for convective mixing it approaches 0.75We propose a generalized KPP model covering the range 0 < Ri < 2 which accounts for both shear and convective mixing in the ocean [ABSTRACT FROM AUTHOR]