WAVE GROUP PROPERTY OF WIND WAVES FROM MODULATIONAL INSTABILITY

Hajime Mase, Yuichi Iwagaki

Abstract


This paper discusses wave grouping of wind waves from the physical viewpoint of wave modulational instability. Amplitude modulation periods obtained from the smoothed instantaneous wave energy history (SIWEH) of the observed data are compared with the predicted values by the modulational instability theory using the Zakharov equation for a finite constant water depth derived by Stiassnie and Shemer(1984). The modulation period normalized by the typical wave period corresponds to the length of total run. It is shown that the amplitude modulation periods of the observed data agree satisfactorily with the predicted values. Thus we conclude that the modulational instability is a hydrodynamical cause of grouping of high waves.

Keywords


wave group; group properties; wind waves; modulational instability

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