Monday, 3 May 2004: 1:45 PM
Impacts of breaking waves and Langmuir circulations on the ocean mixed layer in high winds
Le Jardin Room (Deauville Beach Resort)
The presence of breaking waves are a unique and defining feature of the ocean surface layer in high wind conditions. Wave breaking is dynamically important since it is believed to be the primary path for stress transfer between a wind-generated wave field and the underlying oceanic currents. Further, wave breaking co-exists and interacts with Langmuir circulations, which are generated by vortex forces associated with the wave Stokes drift, and together they promote vigorous mixing of momentum, energy, and scalars in the mixed layer. We examine the interactions between breaking waves, Langmuir circulations and ocean turbulence using a suite of large-eddy simulation (LES) solutions. The LES includes a stochastic model for the effects of breaking waves, developed from laboratory and field data, and adopts the Craik-Leibovich idealization as the model for Langmuir circulations. Preliminary LES results show that a small amount of active breaking significantly alters the instantaneous flow patterns as well as the ensemble statistics. Breaking waves are also found to be effective agents in energizing the surface region of ocean mixed layers and can adequately drive ocean currents in the absence of any other mechanism of momentum transfer from the winds. The interactions with Langmuir circulations and their combined impact on the growth and mixing in the ocean boundary layer are described. Analysis shows how the effective surface roughness z_o increases with wind speed and scales with the breaker field. The potential for comparison with hurricane observations will also be discussed.