The Equilibrium Ranges in Wind—Wave Spectra

Abstract

A review is given of the present ideas on the structure of the equilibrium range in the spectrum of wind-generated gravity waves in deep and shoaling water. It is also shown that an exact analog of Kolmogoroff’s spectrum in a random field of weakly nonlinear surface gravity waves gives a spectral form for frequency spectra S(ω)~ω-4 in close agreement with the results of recent observational studies. A suggestion is made for the description of a “transitional” range of wavenumbers (frequencies), where the deviation from Kolmogoroff’s equilibrium is due to gravitational instability (wavebreaking). Because of this it is suggested that one of the possible equilibrium forms for the spectrum of wind generated waves has two asymptotic regimes: Kolmogoroff’s and Phillips’ type of equilibrium with a relatively rapid transition from the first to the second at high frequencies.