CATKE: a turbulent-kinetic-energy-based parameterization for ocean
microturbulence with dynamic convective adjustment
Abstract
We describe CATKE, a parameterization for ocean microturbulence with
scales between 1 and 100 meters. CATKE is a one-equation model that
predicts diffusive turbulent vertical fluxes a prognostic turbulent
kinetic energy (TKE) and a diagnostic mixing length that features a
dynamic model for convective adjustment (CA). With its convective mixing
length, CATKE predicts not just the depth range where microturbulence
acts but also the timescale over which mixing occurs, an important
aspect of turbulent convection not captured by convective adjustment
schemes. As a result, CATKE can describe the competition between
convection and other processes such as baroclinic restractification or
biogeochemical production-destruction. We estimate CATKE’s free
parameters with a posteriori calibration to
eighteen large eddy simulations of the ocean surface boundary layer, and
validate CATKE against twelve additional large eddy simulations with
stronger and weaker forcing than used during calibration. We find that a
CATKE-parameterized single column model accurately predicts the depth
structure of buoyancy and momentum at vertical resolutions between 2 and
16 meters and with time steps of 10-20 minutes. We propose directions
for future model development, and future efforts to recalibrate CATKE’s
parameters against more comprehensive and realistic datasets.