Upper ocean Langmuir turbulence parameterization in the KPP model in tropical cyclone conditions

Accurate modeling of upper ocean current and temperature fields under tropical cyclones requires ocean boundary layer mixing schemes that maximize accuracy while preserving computational efficiency. First order turbulent flux closure models (such as the KPP model of Large et al. 1994) are commonly employed for this reason. Furthermore, such models are easily modified to incorporate the effects of Langmuir Turbulence that is forced by the Stokes drift of surface waves. We investigate the performance of the KPP model under tropical cyclones with physically based modifications including the use of the Lagrangian eddy viscosity profile (which includes the Stokes drift) and sea state dependent enhancement to the eddy viscosity (based on the turbulent Langmuir number). First, the evolution of the surface wave field is modeled using WAVEWATCH III at selected locations for the duration of simulated historic tropical cyclones and idealized tropical cyclones with varying storm size, intensity, and translation speed. Next, one-dimensional upper ocean simulations are performed using the modified KPP model with the simulated wave field. Finally, the results are compared to high resolution Large Eddy Simulations that include the explicit Stokes drift profile and are performed with the identical wind and wave forcing. Once validated, the modified KPP scheme can be implemented in fully coupled hurricane-wave-ocean models.