Parameterizations and Algorithms for Oceanic Whitecap Coverage

Abstract

hipboard measurements of fractional whitecap coverage W and wind speed at 10-m height, obtained during the 2006 Marine Aerosol Production (MAP) campaign, have been combined with ECMWF wave model and Quick Scatterometer (QuikSCAT) satellite wind speed data for assessment of existing W parameterizations. The wind history trend found in an earlier study of the MAP data could be associated with wave development on whitecapping, as previously postulated. Whitecapping was shown to be mainly wind driven; for high wind speeds (>9 m s?1), a minor reduction in the scatter of in situ W data points could be achieved by including sea state conditions or by using parameters related to wave breaking. The W values were slightly larger for decreasing wind/developed waves than for increasing wind/developing waves, whereas cross-swell conditions (deflection angle between wind and swell waves between ±45° and ±135°) appeared to dampen whitecapping. Tabulated curve fitting results of the different parameterizations show that the errors that could not be attributed to the propagation of the standard error in U10 remained largely unexplained. It is possible that the counteracting effects of wave development and cross swell undermine the performance of the simple parameterizations in this study.