FY 1976

A general model of the ocean mixed layer using a two-component turbulent kinetic energy budget with mean turbulent field closure

Garwood, Jr., R.W.

NOAA Tech. Report ERL 384-PMEL 27, NTIS: PB-265434/1, 81 pp (1976)

A non-stationary, one-dimensional bulk model of a mixed layer bounded by a free surface above and a stable nonturbulent region below is derived. The vertical and horizontal components of turbulent kinetic energy are determined implicitly, along with layer depth, mean momentum, and mean buoyancy. Both layer growth by entrainment and layer retreat in the event of a collapse of the vertical motions due to buoyant damping and dissipation are predicted. Specific features of the turbulent energy budget include mean turbulent field modeling of the dissipation term, the energy redistribution terms, and the term for the convergence of buoyancy flux at the stable interface (making possible entrainment). An entrainment hypothesis dependent upon the relative distribution of turbulent energy between horizontal and vertical components permits a more general application of the model and presents a plausible mechanism for layer retreat with increasing stability. A limiting dissipation time scale in conjunction with this entrainment equation results in a realistic cyclical steady-state for annual evolution of the upper-ocean density field. Several hypothetical examples are solved, and a real case is approximated to demonstrate this response. Of particular significance is the modulation of longer-period trends by the diurnal-period heating/cooling cycle.