On the effect of ocean surface waves on air-sea interactions: results from in-situ and remote measurements in the Gulf of Mexico.

Ocean surface wave full directional spectrum is estimated directly from measurements obtained with a spar buoy and from synthetic aperture radar images of the sea surface. These two techniques complement each other to provide us with a rather comprehensive view of the dynamical behaviour of surface waves. We focus our study in sea state conditions under varying winds, when frequently mixed sea and swell systems are encountered. These conditions are characterized by non-equilibrium wind-wave systems. Direct measurements of ocean-atmosphere momentum fluxes obtained from dedicated air-sea interaction spar buoy are also analyzed. The aim is to better understand the ocean-atmosphere momentum transfer behaviour and uppermost ocean currents under rapidly varying wind field. Atmospheric cold front passage through the measuring buoy imposed a unique wind-wave system information, especially under the occurrence of cases when swell propagation opposes locally generated wind-waves. Of particular importance is the analysis of the wave field making use of synthetic aperture radar images of the sea surface. The wave and wind fields to both sides of the atmospheric front are analyzed. From the buoy measurements fetch-limited wind sea growth is also determined, where slanting fetch is to be considered as very relevant. In particular, wind acceleration effect on wave growth is addressed, during specific cases when wind direction prevailed relatively constant. Wind-wave growth rate is somewhat greater than stationary conditions, as it can be observed also in some laboratory experiments at least for the early stages of the growth process.