Measurements of Breaking Waves
The frequency of whitecapping has been measured with a surface “jump-meter” in wind speeds up to 14 m/s. At this wind speed the proportion of steep or breaking waves was of order 0.05, which is consistent with visual observations of whitecap coverage. Owing to the dispersive property of gravity waves, whitecaps occur intermittently. It is argued that this intermittency, together with the tendency of the air flow to separate preferentially over the steeper waves, causes the horizontal stress exerted by the wind to be both intermittent and patchy. Calculations of the time-dependent flow over steep waves combined with the observed whitecapping frequency suggest that the contribution of intermittent flow separation to the total wind stress is significant.
KeywordsWind Speed Wind Stress Gravity Wave Breaking Wave Horizontal Stress
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