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Free Content A composite vertical current spectrum for strongly and weakly stratified seas and oceans

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An overall frequency (σ) spectrum φ w (σ, N, fh ) is composed for vertical current (w) observations from ocean areas with different stratifications represented by large, 100 m scale buoyancy frequency N. The horizontal Coriolis parameter is denoted by fh . In the open Atlantic Ocean, the relatively strong horizontal layering in density supports the φ w that is found in semiequilibrium under the degradation of the lowest internal wave mode. This φ w is not constant with frequency; however, its variance increases between σ = f and its peak near σ = (0.5 – 0.7) N >> f, where f denotes the local inertial frequency. In contrast, the φ w spectra from the weakly stratified deep Mediterranean and from the shallow North Sea peak at ∼ 1.1 f, except for a tidal peak in North Sea data, and fall off at a rate of σ–1 for 1.1 f < σ < Nm = 4fh , where Nm denotes maximum small-scale N. Background conditions are characterized by vertical instead of horizontal layering in density. Such spectra are best described by a nonequilibrium evolution of small-scale internal waves under a weak mean shear, which transfers variance to σ ≈ f. This φ w Np , p > 0, is contrary to the existing model of open-ocean equilibrium spectra that decrease with N (p < 0). A smooth transition between the two regimes is found to coincide with top-peak φ w for N/fh = 4.
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Keywords: COMPOSITE OCEAN SPECTRUM; INTERNAL WAVES; MIXING EFFECTS; VERTICAL MOTIONS; WEAK AND STRONG STRATIFICATION

Document Type: Research Article

Publication date: January 1, 2015

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  • The Journal of Marine Research, one of the oldest journals in American marine science, publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. Biological studies involving coupling between ecological and physical processes are preferred over those that report systematics. The editors strive always to serve authors and readers in the academic oceanographic community by publishing papers vital to the marine research in the long and rich tradition of the Sears Foundation for Marine Research. We welcome you to the Journal of Marine Research.
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