Abstract
An accurate representation of ocean boundary layer (OBL) turbulent mixing is critical to a climate model. The vertical turbulent mixing parameterization in MPAS-O, K-profile parameterization (KPP), assumes that the vertical turbulent fluxes are given by a strictly specified via a cubic polynomial within the OBL. The maximum of this profile is determined by the surface forcing. Here we present results of comparisons of KPP against numerous large eddy simulation (LES) configurations. In LES the dominant eddies, which are responsible for boundary layer mixing, are explicitly resolved. The LES have widely different surface forcing and initial configuration. The strength of wind, temperature, and salinity forcing are varied as well as the initial temperature and salinity profile. Results will be presented that have been used to improve the simulation of the OBL in MPAS-O. Despite many improvements to KPP and MPAS-O, results from various configurations show that critical issues remain. For example, KPP can cause warming when the only surface forcing is cooling and can lead to negative concentrations of BGC in the presence of strong surface forcing and small OBL concentrations. Further, KPP can create negative diffusivities in the presence of large interior diffusivities near the OBL.
Given these results, we suggest a possible new representation for vertical mixing that assumes