Field Investigation of Transformation of the Wind Wave Frequency Spectrum with Fetch and the Stage of Development

Abstract

The variability of frequency spectra of waves is considered; for example, the dependencies of integral and spectral parameters of waves on wave-development factors and the interrelationships of the parameters are examined. Also studied is the transformation of the frequency spectrum shape in the course of its development, as well as the transition from the spectrum of developing waves to the spectrum of fully developed waves. Data were obtained in situ with common methods during a long-term program in the Black Sea. The variability of the spectrum of developing waves, as a function of the stage of wave development, is described on the basis of field data using estimates of parameters for the spectrum form of the JONSWAP type. A novel approximation of the equilibrium interval level dependence on the dimensionless peak frequency f?m is obtained, which includes periods of stable and changeable behavior of the spectrum level. Transformation of the spectrum of wind-generated waves related to the development of the wave field in terms of the JONSWAP spectrum form is obtained. Continuous transition to the Pierson?Moskowitz spectrum is described. An approximation of the dependence of the enhancement coeffiecient ? on wave development stage f?m is suggested, which describes continuous variation of the coefficient ? for all wave ages. Self-similarity of the spectrum of developing waves is not observed.