MODELING WAVE-ENHANCED TURBULENCE IN THE OCEAN SURFACE-LAYER

Until recently, measurements below the ocean surface have tended to co nfirm ''law of the wall'' behavior, in which the velocity profile is l ogarithmic, and energy dissipation decays inversely with depth. Recent measurements, however, show a sublayer, within meter; of the surface, in which turbulence is enhanced by the action of surface waves. In th is layer, dissipation appears to decay with inverse depth raised to a power estimated between 3 and 4.6. The present study shows that a conv entional model, employing a ''level 21/2'' turbulence closure scheme, predicts near-surface dissipation decaying as inverse depth to the pow er 3.4. The model shows agreement in detail with measured profiles of dissipation. This is despite the Bet that empirical constants in the m odel are determined for situations very different from this near-surfa ce application. The action of breaking waves is modeled by a turbulent kinetic energy input at the surface. In the wave-enhanced layer, the downward nux of turbulent kinetic energy balances its dissipation. The model produces analytic descriptions for the depth of the layer, and for profiles of velocity, turbulent kinetic energy, and dissipation. T he surface roughness length (in the water) is a critical parameter in the solutions. There are indications of a relationship between the rou ghness length and surface wave parameters, such as the amplitude or in verse wavenumber. Roughness lengths at least up to 1 m appear to be fe asible.