Improving simulations of the upper ocean by inclusion of surface waves in the Mellor-Yamada turbulence scheme

The Mellor-Yamada turbulence closure scheme, used in many ocean circulation models, is often blamed for overly high simulated surface temperature and overly low simulated subsurface temperature in summer due to insufficient vertical mixing. Surface waves can enhance turbulence kinetic energy and mixing of the upper ocean via wave breaking and nonbreaking-wave-turbulence interaction. The influences of wave breaking and wave-turbulence interaction on the Mellor-Yamada scheme and upper ocean thermal structure are examined and compared with each other using one-dimensional and three-dimensional ocean circulation models. Model results show that the wave-turbulence interaction can effectively amend the problem of insufficient mixing in the classic Mellor-Yamada scheme. The behaviors of the Mellor-Yamada scheme, as well as the simulated upper ocean thermal structure, are significantly improved by adding a turbulence kinetic energy production term associated with wave-turbulence interaction. In contrast, mixing associated with wave breaking alone seems insufficient to improve significantly the simulations as its effect is limited to the very near-surface layers. Therefore, the effects of wave-turbulence interaction on the upper ocean are much more important than those of wave breaking.