Wave effects on subsurface turbulence: a comparison between observations and large eddy simulations

Langmuir circulation (LC) and breaking waves are turbulent processes driven by wind and surface waves that influence mixing dynamics of the oceanic surface boundary layer. Utilizing turbulence measurements and numerical models combined with recent understanding of wind-wave coupling, we systematically compare observations and simulations of the wave-influenced surface boundary layer. The numerical model is based on a large eddy simulation (LES) that explicitly incorporates turbulent processes due to LC, buoyancy, shear, and breaking waves. To investigate the interaction between LC and breaking waves, the LES is combined with a coupled wind and wave model, which includes the effect of breaking waves, while satisfying the conservation of momentum and energy. To gain insights into wave effects on subsurface turbulence, simulations are run with and without wave forcing. Data sets obtained from a previous field experiment in the eastern North Pacific (Surface Waves Process Program) provide unique subsurface turbulence observations. Model results of the temporal velocity spectrum evolution as well as surface cross-wind root mean square velocities agree significantly better with observations, if wave effects are included in the simulations. Observed blobs of denser and lighter fluid suspended within the mixed layer are only captured by LES with LC effect. Model results provide evidence for the critical role of wave-current interactions in mixed layer dynamics.