Estimates of wave breaking energy dissipation rate from measurements of whitecap coverage

Abstract

The easiest way to identify the occurrence, or recent occurrence of oceanic air-entraining breaking waves (whitecaps) from above the water surface is through photographic remote sensing of the sea surface. In this paper I estimate the energy dissipation rate due to breaking wave whitecaps using measurements of whitecap coverage of the sea surface. Several datasets are used that employed different methodologies for determining the whitecap coverage spanning almost 4 decades of research. The results show that, on average, the ratio of the energy dissipation rate due to whitecaps to the wind energy input rate to the upper ocean and wave field is close to unity above wind speeds of about 10 m s-1. Below 10 m s-1, this energy flux ratio decreases steadily from unity as wind speed decreases, in agreement with several recent studies. The implication is that other dissipative processes play an important role in dissipating the wind energy input to the upper ocean and wave field at low wind speeds. These results suggest that variability in this energy flux ratio may be responsible for differences in measurements and parameterisations of whitecap coverage at low wind speeds.