Laboratory measurements of ocean surface drag in extreme wind and wave conditions

Air-sea drag in hurricane wind and wave conditions remains largely unknown and difficult to measure in the field. Here we revisit the momentum budget approach to estimate the air-sea drag coefficient in extreme wind conditions in the laboratory. To bridge the gap between young windsea in the laboratory and mature sea-state in the field, we measure the drag coefficient in strong winds with and without mechanically generated background waves in the SUSTAIN wind-wave laboratory at the University of Miami. Our new drag estimates, based on momentum budget and eddy-covariance methods in wind-only conditions, agree with field measurements in low-to-moderate winds, and previous laboratory measurements in hurricane-force winds. Introducing a background wave field increases the drag coefficient beyond the previously established level of saturation, suggesting that the wind-only laboratory studies may be underestimating the drag coefficient. The drag saturation is correlated with the limit in the wave development. Our results suggest that the drag coefficient estimates in the laboratory are largely dependent on the level of wave development. We will also present new laboratory measurements of drag coefficient in major hurricane-force winds up which have not been previously studied.