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 Ri(f) approaches 0.5, while for pure convective mixing the mixing efficiency Ri(f) 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 Ri, we also formulate a modified version of the empirical KPP model for parameterizing ocean mixing in numerical models.