An energetically consistent vertical mixing parameterization in CCSM4

An energetically consistent stratification-dependent vertical mixing parameterization is implemented in the Community Climate System Model 4 and forced with energy conversion from the barotropic tides to internal waves. The structures of the resulting dissipation and diffusivity fields are compared to observations, and the fidelity of the resulting temperature fields is assessed. Compared to existing biases in the control simulation, differences in surface fields are small, showing that the surface climate state is relatively robust to the choice of mixing parameterization. The thermocline structure, however, depends greatly on the details of the vertical mixing parameterizations, where the new energetically consistent parameterization results in low thermocline diffusivities and a sharper and shallower thermocline. It is also investigated if the ocean state is more sensitive to a change in forcing if the energetically consistent scheme is used compared to a tidal mixing parameterization with fixed background diffusivity. In particular we find that the Atlantic Meridional Overturning Circulation is more sensitive to changes in the Southern Ocean wind stress with the former. However, in line with previous results, changes to Southern Ocean upwelling are still largely compensated by changes to the diabatic upwelling in the Indo-Pacific basin.