A New Langmuir Turbulence Parameterization for Ocean Models Developed Under Realistic Forcing Conditions.

Langmuir turbulence (LT) has been shown to significantly increase vertical mixing rates in the ocean surface boundary layer, resulting in increased momentum and heat transfer. This enhancement is usually represented in ocean models through modifications to the turbulent eddy viscosity, modeled via either turbulent closure or K-Profile Parameterization (KPP) schemes. This study presents a new parameterization based on the KPP scheme to account for the enhancement of the eddy viscosity due to LT under realistic forcing conditions. Large Eddy Simulations (LES) performed at Ocean Water Station Papa were used for the development of the parameterization. The LES model was initialized from observed temperature and salinity profiles, and forced by observed heat flux and wind. Stokes drift current is computed from observed 2D wave spectra. The parameterization presented here uses a modified Langmuir number, which uses Stokes shear instead of velocity at the surface, to account for the enhancement due to LT. A set of idealized LES experiments using a range of different wind-wave angles is used to guide the parameterization on the effect of wind-wave misalignment. Finally, the shape function is modified to account for the interaction of surface heat flux and Stokes shear. The new parameterization is implemented in the Navy Coastal Ocean Model, and 1D simulations are performed using the same initial profiles and forcing conditions as the LES experiments. Results from this model implementation are presented and compared to simulations based on the turbulence closure models by Kantha-Clayson (2004) and Harcourt (2015). The implementation is shown to be able to adequately represent eddy viscosity profiles within the mixed layer when compared to LES results.