Mesoscale to Submesoscale Wavenumber Spectra in Drake Passage

Abstract

This study discusses the upper-ocean (0-200 m) horizontal wavenumber spectra in the Drake Passage from 13 yr of shipboard ADCP measurements, altimeter data, and a high-resolution numerical simulation. At scales between 10 and 200 km, the ADCP kinetic energy spectra approximately follow a k 23 power law. The observed flows are more energetic at the surface, but the shape of the kinetic energy spectra is independent of depth. These characteristics resemble predictions of isotropic interior quasigeostrophic turbulence. The ratio of across-track to along-track kinetic energy spectra, however, significantly departs from the expectation of isotropic interior quasigeostrophic turbulence. The inconsistency is dramatic at scales smaller than 40 km. A Helmholtz decomposition of the ADCP spectra and analyses of synthetic and numerical model data show that horizontally divergent, ageostrophic flows account for the discrepancy between the observed spectra and predictions of isotropic interior quasigeostrophic turbulence. In Drake Passage, ageostrophic motions appear to be dominated by inertia-gravity waves and account for about half of the near-surface kinetic energy at scales between 10 and 40 km. Model results indicate that ageostrophic flows imprint on the sea surface, accounting for about half of the sea surface height variance between 10 and 40 km.

The Impact of Horizontal Resolution on Energy Transfers in Global Ocean Models

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Temporal Changes in the Antarctic Circumpolar Current: Implications for the Antarctic Continental Shelves

“…As higher-resolution measurement and modeling capabilities become more available, additional mechanisms may become evident that also contribute to crossshelf transport of heat. Studies to date have largely focused on the role of mesoscale eddies, but emerging work suggests that tides and internal waves could account for a significant fraction of highfrequency, high-wavenumber variability in the Southern Ocean (e.g., Rocha et al, 2016) and thus could potentially modulate meridional transport mechanisms in ways that have not been explored with existing models. Mechanism 1 (a southward displacement of the velocity jet structures and corresponding sloping isopycnals that define the ACC in response to a southward shift in winds) is not supported by decadal-scale altimeter observations.…”

Climate Process Team on Internal Wave–Driven Ocean Mixing

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