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Abstract In this study, we diagnose the spatial variability in the energetics of tidally generated diurnal, semidiurnal, and supertidal ( cycles per day) internal wave vertical modes (up to mode 6) in a 30‐day forward global ocean model simulation with a 4‐km grid spacing and 41 layers. The simulation is forced with realistic tides and atmospheric fields. Diurnal modes are resolved beyond mode 6, semidiurnal modes are resolved up to mode 4, and supertidal modes are resolved up to mode 2, in agreement with a canonical horizontal resolution criterion. The meridional trends in the kinetic to available potential energy ratios of these resolved modes agree with an internal wave consistency relation. The supertidal band is dominated by the higher harmonics of the diurnal and semidiurnal tides. Its higher harmonic energy projects on the internal wave dispersion curves in frequency‐wavenumber spectra and is captured mostly by the terdiurnal and quarterdiurnal mode‐1 waves. Terdiurnal modes are mostly generated in the west Pacific, where diurnal internal tides are strong. In contrast, quarterdiurnal modes occur at all longitudes near strong semidiurnal generation sites. The globally integrated energy in the supertidal band is about one order of magnitude smaller than the energy in the tidal band. The supertidal energy as a fraction of the tidal energy is elevated along semidiurnal internal wave beams in the tropics. We attribute this to near‐resonant interactions between tidal modes of the same mode number.
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Probing the Nonlinear Interactions of Supertidal Internal Waves Using a High-Resolution Regional Ocean Model
Abstract The internal wave (IW) continuum of a regional ocean model is studied in terms of the vertical spectral kinetic energy (KE) fluxes and transfers at high vertical wavenumbers. Previous work has shown that this model permits a partial representation of the IW cascade. In this work, vertical spectral KE flux is decomposed into catalyst, source, and destination vertical modes and frequency bands of nonlinear scattering, a framework that allows for the discernment of different types of nonlinear interactions involving both waves and eddies. Energy transfer within the supertidal IW continuum is found to be strongly dependent on resolution. Specifically, at a horizontal grid spacing of 1/48°, most KE in the supertidal continuum arrives there from lower-frequency modes through a single nonlinear interaction, whereas at 1/384° and with sufficient vertical resolution KE transfers within the supertidal IW continuum are comparable in size to KE transfer from lower-frequency modes. Additionally, comparisons are made with existing theoretical and observational work on energy pathways in the IW continuum. Induced diffusion (ID) is found to be associated with a weak forward frequency transfer within the supertidal IW continuum. ID is also limited to the highest vertical wavenumbers and is more sensitive to resolution relative to spectrally local interactions. At the same time, ID-like processes involving high-vertical-wavenumber near-inertial and tidal waves as well as low-vertical-wavenumber eddy fields are substantial, suggesting that the processes giving rise to a Garrett–Munk-like spectra in the present numerical simulation and perhaps the real ocean may be more varied than in idealized or wave-only frameworks.
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- PAR ID:
- 10487219
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Physical Oceanography
- Volume:
- 54
- Issue:
- 2
- ISSN:
- 0022-3670
- Format(s):
- Medium: X Size: p. 399-425
- Size(s):
- p. 399-425
- Sponsoring Org:
- National Science Foundation
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