Research and development of wave-forecasting models of the next generation

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The purpose of this research therefore was not only to develop technique for improving the wave-forecasting model, but also to study wide aspects of wind-wave phenomena associated with the wave model. Hence the principal results are classified into the two categories :(A) Technical achievements in the wave forecasting model :1. Intercomparison of the RIAM model and the well-known WAM model or others2. Development of the method for calculating nonlinear energy transfer at finite depths3. Development and test of algorithms for the radiation term of the spectral evolution(B) Wave-dynamical findings and problems :1. Statistics of wind and waves observed at the Tsuyazaki Station and in the Japan Sea2. Experimental study of wave braking especially on its role in redelivering energy3. Nonlinear dispersion relation and equilibrium spectra of wind-wave spectraResults of particular interest to be highlighted are as follows.1) A method was developed for calculating the nonlinear energy transfer among component waves at "finite depth". The method much improves the previous methods of Masuda (1980) or Komatsu and Masuda (1996, the RIAM method).the method developed here is probably is one of the most reliable with a widest applicability both in deep water and in shallow water.2) Wave breaking has so far been considered simply as an energy sink. The experiment made in this research, however, clearly indicated that braking redistributes energy among component waves just as nonlinear energy transfer does.3) The long-term data analysis revealed that the steepness of significant waves in the Japan Sea has an upper bound independent of the season of the wind speed. Also it was found that significant wave heights and significant wave periods have -5/3 power frequency spectra for periods from a few dayst to several hours. These findings suggest the presence of some deeper laws about the variability of "significant waves", which should be a consequence of some unknown dynamics.