The Ability of Large-Scale Ocean Models to Accept Parameterizations of Boundary Mixing, and a Description of a Refined Bulk Mixed-Layer Model

There are a number of barriers to the adoption of improved parameterizations of diapycnal mixing in large-scale ocean models. Two such barriers are discussed in detail. Ocean models often exhibit levels of spurious numerical diapycnal mixing that are so large, compared with the physical values, that parameterizing additional mixing is counterproductive, even when that additional mixing is physically well motivated. In addition, model resolution can inhibit the inclusion of observationally motivated mixing parameterizations. The remedy to the spurious diapycnal mixing lies with improved numerical algorithms or with the use of isopycnic ocean models that avoid this difficulty altogether. Selectively enhancing the resolution can greatly improve the ability of an ocean model to accept parameterizations of subgridscale physical processes. This last point is illustrated by considering the representation of dense water overflows in largescale ocean models of several classes. It is also illustrated with a refined bulk mixed layer, in which added degrees of freedom within the mixed layer allow both resolved and parameterized shear-driven restratification, with a dramatic impact on the modeled mixed-layer depth. This refined bulk mixed layer in conjunction with an isopycnic interior model may prove to be a viable alternative approach to hybrid pressure-isopycnic coordinate models for the treatment of near-surface processes in large-scale ocean models, and it is described in detail.