Breaking Waves and Near-Surface Turbulence

Abstract

Breaking deep-water surface waves play an important role in many aspects of air–sea interaction, including transfer of momentum, gases and heat, dissipation of wave energy, and the generation of sea spray and aerosols. Of further practical importance are their dispersion of nutrients and pollutants and the generation of ambient sound. Breaking waves are most commonly associated with whitecaps. Wave breaking occurs at scales ranging from centimeters up to the dominant waves but microbreakers cause no visible air entrainment. Nonlinear wave hydrodynamics seem to form the path to wave breaking. Mean turbulence levels in a wind-driven sea are 1–2 orders of magnitude larger than would occur in an equivalent flow along a rigid boundary. The turbulence enhancement is largest close to the surface, with the depth of the wave enhanced layer reaching a few meters. Instantaneous levels of turbulence energy dissipation beneath actively breaking waves can reach more than 4 orders of magnitude enhancement, but turbulence decays rapidly. The concept of relating wave breaking dynamics to the length and propagation speed of breaking crests is suitable for remote observation techniques and may prove to be a valuable tool in solving some of the outstanding issues related to wave breaking.