Sea‐Surface Slope and Equilibrium Wind‐Wave Spectra

The measured mean‐square slope of the sea surface is shown to vary logarithmically with the wind velocity, and the rates of variation change with different boundary‐layer regimes of the wind. Based on mean‐square slope data, the form of a newly proposed equilibrium wind‐wave spectrum for the capillary range is verified, the spectral coefficients for both gravity and capillary ranges are determined, and the cutoff wavenumber for the slope data is shown to be much smaller than the neutrally stable wavenumber obtained from laminar model. Finally, an approximate correlation is presented between the mean‐square slope and the roughness height of the sea surface, implying that the growth of small waves is mainly due to the direct action of the wind.