A Modification of the Garrett–Munk Internal Wave Spectrum

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Abstract
The Garrett–Munk (GM) spectrum continues to be a useful description of the oceanic internal wave field. However, there are several inconsistencies and ambiguities that make it difficult to use in comparing internal wave fields at different latitudes, stratifications, and water depths. A modified spectral formulation is presented that treats three problems with the Garrett–Munk formulation: the normalization of the energy spectrum as a function of frequency bandwidth, the energy distribution at frequencies below the semidiurnal tide, and the treatment of vertical boundaries and turning points. Addressing these problems leads to a substitution of the GM parameters E (nondimensional energy), b (vertical length scale), and N0 (buoyancy frequency scale) with two new dimensional scales: Eref, the energy per unit mass, and D(ω), the Wentzel–Kramers–Brillouin (WKB)-scaled thickness of the vertical waveguide. The advantages of the modified spectrum are illustrated by comparing with observations from the equator and the continental shelf.

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