The numerical studies of the formation processes of the universal internal wave spectrum in the deep ocean

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As a basic study for an accurate parameterization of turbulent diffusivity in the deep ocean, the formation processes of the universal ocean internal wave spectrum are investigated using a fine-grid numerical model forced with both the tidal- and windforcings. It is found that, only when both the tidal- and wind- forcings are applied, the universal Garrett-Munk (GM) spectrum as observed in the real ocean can be successfully reproduced independent of the ratio of each forcing. Especially, it is shown that the cascade of internal wave energy is enhanced around the latitude of 30° through nonlinear resonant triad interaction mechanism called parametric subharmonic instability. It is also indicated that low-vertical mode internal tides can propagate a long distance more than 10000km across the open ocean, suggesting that they play important roles in maintaining the universal energy level of the GM spectrum.