SURFACE WAVE-TURBULENCE INTERACTIONS - SCALING EPSILON(Z) NEAR THE SEA-SURFACE

A freely rising profiler was used to collect vertical microstructure p rofiles in the upper oceanic boundary layer under various atmospheric and sea conditions. Near the sea surface, the rate of viscous dissipat ion of turbulence kinetic energy, epsilon, exhibited a range of behavi ors under different forcing conditions. Sometimes, epsilon was closely balanced by the wind stress production of turbulence kinetic energy. At other times, epsilon was greatly enhanced relative to wind stress p roduction and exhibited an exponential depth decay. In these instances , simple scaling laws predicted for turbulence near a solid surface se verely underestimate turbulent mixing near the ocean surface. Plausibl e explanations for enhanced epsilon(z) near the sea surface will have to address the effects of wave-turbulence interactions. The authors pr opose two different mechanisms to explain the behavior of epsilon near the surface, leading to two scaling schemes. The first mechanism requ ires high levels of turbulence kinetic energy, created by wave breakin g at the surface, to be transported downward away from the surface by the motion of the swell. This transport is then locally balanced by ep silon. The second mechanism requires a rotational wave field and signi ficant wave stresses that balance the turbulence Reynolds stresses. En ergy drawn from the wave field to the mean flow, via the wave stresses , is in turn drawn from the mean flow by the turbulence production ter m, which is balanced by epsilon.