Comparing estimates of whitecap coverage from a spectral wave model with oceanic observations.

The fractional or percentage whitecap coverage of the ocean surface (W) is often parameterized in
terms of wind speed. Data sets of W typically show order of magnitude scatter at a given wind speed value due to
sea state variability. Here we compare modeled values of W to measured W values from the North Atlantic
Ocean. The modeled W is forced by the spectrally integrated whitecap dissipation source function in the
European Center for Medium‐Range Weather Forecasts spectral wave model, ecWAM. Without tuning, best
agreement is found for mature sea states, with an average modeled to measured W ratio of 0.87. This ratio
approaches unity with the introduction of a dissipation rate threshold value and an explicit wave‐age
dependence. The study suggests that accurate estimates of W can be routinely produced by ecWAM and opens
new opportunities to model bubble‐mediated fluxes of CO2 and sea spray aerosol with ecWAM.