Wave-Coherent Air–Sea Heat Flux

Abstract

Abstract Air–sea fluxes of heat and momentum play a crucial role in weather, climate, and the coupled general circulation of the oceans and atmosphere. Much progress has been made to quantify momentum transfer from the atmosphere to the ocean for a wide range of wind and wave conditions. Yet, despite the fact that global heat budgets are now at the forefront of current research in atmospheric, oceanographic, and climate problems and despite the good research progress in recent years, much remains to be done to better understand and quantify air–sea heat transfer. It is well known that ocean-surface waves may support momentum transfer from the atmosphere to the ocean, but the role of the waves in heat transfer has been ambiguous and poorly understood. Here, evidence is presented that there are surface wave–coherent components of both the sensible and the latent heat fluxes. Presented here are data from three field experiments that show modulations of temperature and humidity at the surface and at 10–14 m above the surface, which are coherent with the surface wave field. The authors show that the phase relationship between temperature and surface displacement is a function of wind speed. At a 10–12-m elevation, a wave-coherent heat transfer of O(1) W m−2 is found, dominated by the latent heat transfer, as well as wave-coherent fractional contributions to the total heat flux (the sum of latent and sensible heat fluxes) of up to 7%. For the wind speeds and wave conditions of these experiments, which encompass the range of global averages, this wave contribution to total heat flux is comparable in magnitude to the atmospheric heat fluxes commonly attributed to the effects of greenhouse gases or aerosols. By analogy with momentum transfer, the authors expect the wave-coherent heat transfer to decay with height over scales on the order of k−1, where k is the characteristic surface wavenumber; therefore, it is also expected that measurements at elevations of O(10) m may underestimate the contribution of the wave-induced heat flux to the atmosphere.