Dynamics of turbulence production by attenuating interfacial gravity waves observed in air-water coupled wave-resolving simulation

Even without breaking or wind influence, ocean surface waves are observed to produceturbulence in the water, possibly influencing ocean surface dynamics and air-seainteractions. Based on the water-side free-surface simulations, recent studies suggestthat such turbulence is produced through the interaction between the waves and thenear-surface Eulerian current associated with the viscous attenuation of waves. To clarifythe dynamical role of the air-water interface in the turbulence production, the attenuatinginterfacial gravity waves weresimulateddirectly using a newly developed two-phasewave-resolving numerical model. The air-water coupling enhanced the wave energydissipation through the formation of a strong shear at the air-side viscous boundarylayer. This led to an enhancement of the wave-to-current momentum transfer and theformation of the down-wave Eulerian mean sheared current, which is favourable for theCL2 instability responsible for the production of Langmuir circulations. As a result,the water-side turbulence grew stronger comparedwith the corresponding free surface(water-only) wave-resolving simulation. The evolution of the wave-averaged field waswell reproduced with the Craik-Leibovich equation with the upper boundary conditionprovided with the virtual wave stress based on linear theory. The wave energy dissipationby air-water coupling plays a significant role in the quantitative understanding of thewave-induced turbulence at the laboratory and field scales