Dissipation function of wind seas and wave parameterization of whitecap coverage

The whitecap coverage in the ocean is considered to be proportional to the dissipation of the wave field. The dissipation function of fetch- or duration-limited wave fields can be expressed in terms of wind and global wave parameters (wind speed, significant wave height and peak wave frequency). With the aid of the empirically established fetch-limited growth functions, the dissipation function is shown to be proportional to the product of (reference wind speed) cube, (dimensionless frequency) cube and (dimensionless energy). For a wide range of wave growth conditions the (dimensionless energy) is inversely proportional to the cube of (dimensionless frequency), and the dependence on explicit wave parameters becomes very weak. This may explain why it is so elusive to find a reliable dependence of whitecap coverage on wave parameters and that the power-law wind speed dependence with an exponent close to three remains the most robust empirical relationship describing the whitecap coverage in the ocean. The result from comparisons of the developed dissipation function with available whitecap observations with wave measurements and the closely related phenomenon of radar sea spikes is encouraging.