A COMPARISON OF VERTICAL EDDY MIXING PARAMETERIZATIONS FOR EQUATORIALOCEAN MODELS

The vertical eddy mixing formulations employed in the K-theory model o f Pacanowski and Philander and in second-moment closure models are com pared for an equatorial Pacific Ocean simulation. The Pacanowski and P hilander model is found to be mainly driven by changes in the stratifi cation rather than shear-generated instabilities, and the position and width of the mixing transition zone between high and low mixing value s is found to be sensitive to the parameters of the model. In the seco nd-moment closure models the master length scale limit effectively det ermines the threshold of the mixing zone, while the inclusion of stora ge, advection, and diffusion terms in the turbulent kinetic energy equ ation affects both the position and extent of the transition zone. Vis cous mixing is more intense than diffusive mixing in the Pacanowski an d Philander scheme, but in the second-moment closure models the revers e tends to be true. As expected, there is no simple functional relatio nship between the gradient Richardson number and the intensity of mixi ng in the second-moment closure schemes.