A Scale-aware Parameterization of Restratification Effect of Turbulent Thermal Wind Balance

The vertical buoyancy flux (Bf) under the turbulent thermal wind (TTW) balance, BfTTW, plays an important role in restratifying the surface mixed layer in winter. So far most of the global ocean models are too coarse to resolve this process. In this paper, a scale-aware parameterization is proposed for BfTTW and implemented in a hierarchy of regional ocean simulations over the winter Kuroshio extension with horizontal resolutions ranging from 27 km to 1 km. The parameterization depends on the Coriolis parameter, model-simulated turbulent vertical viscosity, horizontal density gradient and a scaling relationship to adjust for the effects of model horizontal resolution on the simulated horizontal density gradient. It shows good skills in reconciling the difference between BfTTW in the coarse-resolution simulations (27 km, 9km and 3 km) and in the 1-km simulation where BfTTW is well resolved. Furthermore, implementation of the parameterization improves the simulated stratification in the surface mixed layer in coarse-resolution simulations.