For many years it has been assumed that the atmospheric boundary layer over the sea behaves in a manner similar to that over land. Yet the two interfaces are fundamentally different in that the former is a dynamic boundary, responding to and coupled with the atmosphere, while the latter is essentially static. The height of the wave affected layer over the water has been estimated to be O(1m), well below typical measurement heights in the field (Makin and Mastenbroek 1996).
Here we present measurements of momentum flux (eddy correlation), velocity profiles and directional wave spectra from a research tower. In conditions of pure wind sea, there is indeed no evidence for a wave induced component of the stress at heights down to 2m (Hs = 1.4m). By contrast, in conditions of light winds propagating with strong swell, wave effects were found up to 12m above the surface (Hs = 1.2m).
We discuss the implications of these measurements with respect to the applicability of Monin-Obukhov similarity theory and the inertial dissipation method of estimating fluxes over the sea.