Rapid generation of high‐frequency internal waves beneath a wind and wave forced oceanic surface mixed layer

Abstract

High‐frequency internal waves generated by Langmuir motions over stratified water may be an important source of turbulent mixing below the surface mixed layer. Large eddy simulations of a developing mixed layer and inertial current are employed to investigate this phenomena. Uniform surface wind stress and parallel Stokes drift wave forcing rapidly establishes a turbulent mixed‐layer flow, which (as the inertial motion veers off the wind) generates high‐frequency internal waves in the stratified fluid below. The internal waves evolve such that their vector phase velocity matches the depth‐averaged mixed‐layer velocity that rotates as an inertial oscillation. The internal waves drain energy and momentum from the mixed layer on decay time‐scales that are comparable to those of near‐inertial oscillations. The high‐frequency waves, which are likely to be trapped in the transition layer, may significantly contribute to mixing there and thus provide a potentially important energy sink for mixed‐layer inertial motions.