Formulation and Calibration of CATKE, a One‐Equation Parameterization for Microscale Ocean Mixing

Abstract

We describe CATKE, a parameterization for fluxes associated with small‐scale or “microscale”ocean turbulent mixing on scales between 1 and 100 m. CATKE uses a downgradient formulation that dependson a prognostic turbulent kinetic energy (TKE) variable and a diagnostic mixing length scale that includes adynamic convective adjustment (CA) component. With its dynamic convective mixing length, CATKE predictsnot just the depth spanned by convective plumes but also the characteristic convective mixing timescale, animportant aspect of turbulent convection not captured by simpler static CA schemes. As a result, CATKE candescribe the competition between convection and other processes such as shear‐driven mixing and baroclinicrestratification. To calibrate CATKE, we use Ensemble Kalman Inversion to minimize the error between 21large eddy simulations (LESs) and predictions of the LES data by CATKE‐parameterized single columnsimulations at three different vertical resolutions. We find that CATKE makes accurate predictions of bothidealized and realistic LES compared to microscale turbulence parameterizations commonly used in climatemodels.