Implications of Ocean Bottom Reflection for Internal Wave Spectra and Mixing

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  • 1 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge. MA 02139
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Abstract

A linear internal wave model for reflection off a sloping bottom applied to a field of horizontally isotropic waves typical of the deep ocean leads to a strongly perturbed frequency-vertical wavenumber energy spectrum. The spectrum is dominated by a nonintegrable singularity at the internal wave critical frequency characteristic of the environment and bottom slope. An observational requirement that the internal wave spectrum near the bottom relax to the open deep-ocean level and shape within a few hundred meters vertically implies a flux imbalance normal to the boundary. The flux that must be redistributed over the internal wave spectrum, or lost from it, amounts to O(10−2 W m−2), larger than for most other energy transfer mechanisms estimated for internal waves. A small fraction of this flux imbalance applied to mixing can account for a basin-averaged effective vertical diffusivity of 10−4 m2 s−1. Bottom reflection represents not only a likely and powerful sink for internal wave energy, but a mechanism that may be important to the oceanic general circulation through its contribution to mixing.

Abstract

A linear internal wave model for reflection off a sloping bottom applied to a field of horizontally isotropic waves typical of the deep ocean leads to a strongly perturbed frequency-vertical wavenumber energy spectrum. The spectrum is dominated by a nonintegrable singularity at the internal wave critical frequency characteristic of the environment and bottom slope. An observational requirement that the internal wave spectrum near the bottom relax to the open deep-ocean level and shape within a few hundred meters vertically implies a flux imbalance normal to the boundary. The flux that must be redistributed over the internal wave spectrum, or lost from it, amounts to O(10−2 W m−2), larger than for most other energy transfer mechanisms estimated for internal waves. A small fraction of this flux imbalance applied to mixing can account for a basin-averaged effective vertical diffusivity of 10−4 m2 s−1. Bottom reflection represents not only a likely and powerful sink for internal wave energy, but a mechanism that may be important to the oceanic general circulation through its contribution to mixing.

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