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- Title
Nonlinear Internal Tides in a Realistically Forced Global Ocean Simulation.
- Authors
Solano, Miguel S.; Buijsman, Maarten C.; Shriver, Jay F.; Magalhaes, Jorge; da Silva, Jose; Jackson, Christopher; Arbic, Brian K.; Barkan, Roy
- Abstract
The decay of the low‐mode internal tide due to the superharmonic energy cascade is investigated in a realistically forced global Hybrid Coordinate Ocean Model simulation with 1/25° (4 km) horizontal grid spacing. Time‐mean and depth‐integrated supertidal kinetic energy is found to be largest near low‐latitude internal tide generation sites, such as the Bay of Bengal, Amazon Shelf, and Mascarene Ridge. The supertidal kinetic energy can make up to 50% of the total internal tide kinetic energy several hundred kilometers from the generation sites. As opposed to the tidal flux divergence, the supertidal flux divergence does not correlate with the barotropic to baroclinic energy conversion. Instead, the time‐mean and depth‐integrated supertidal flux divergence correlates with the nonlinear kinetic energy transfers from (sub)tidal to supertidal frequency bands as estimated with a novel coarse‐graining approach. The regular spaced banding patterns of the surface‐intensified nonlinear energy transfers are attributed to semidiurnal mode 1 and mode 2 internal waves that interfere constructively at the surface. This causes patches where both surface tidal kinetic energy and nonlinear energy transfers are elevated. The simulated internal tide off the Amazon Shelf steepens significantly near these patches, generating solitary‐like waves in good agreement with Synthetic Aperture Radar imagery. Globally, we find that regions of high supertidal energy flux also show a high correlation with observed instances of internal solitary waves. Plain Language Summary: Ocean tides generate internal waves at steep ridges and continental shelves in a stratified ocean. In some regions with strong tidal forcing, surface intensified stratification, and weak background rotation, these waves are observed to steepen into solitary‐like waves. In this process, energy is transferred from the tidal band to higher (supertidal) frequencies and wavenumbers. This study investigates "internal tide steepening" in a realistically forced global Hybrid Coordinate Ocean Model (HYCOM) simulation with a 4‐km horizontal grid spacing. In our simulation, supertidal internal wave energy accounts for about 5% of the total energy available to internal tides equatorward of ±25°. However in some regions, such as the Amazon Shelf and Bay of Bengal, this ratio can be as much as 50%. Along the internal tide beams, the supertidal energy transfers are enhanced in regular spaced "patches" where longer and faster mode 1 semidiurnal internal tides overtake the shorter and slower mode 2 internal tides. In these patches the surface velocities of these waves constructively superpose, enhancing the surface kinetic energy and nonlinear energy transfers. At the Amazon Shelf, sharp‐crested solitary‐like waves that emerge in these patches in the HYCOM simulation are in good agreement with satellite observations. Although nonlinear internal tides are simulated in our global ocean model simulation, higher resolutions are needed to better resolve the energy cascade to smaller scales. Key Points: Supertidal energy (>2.67 cycles per day [cpd]) is elevated at low latitudes, making up to 50% of total tidal energy (>0.9 cpd) in some areasSupertidal flux divergence and surface tidal energy reveal banding patterns due to the interaction between mode 1 and 2 internal tidesSupertidal flux divergence is due to energy transfers from internal tides to higher‐harmonic frequencies as computed with coarse graining
- Subjects
INTERNAL waves; KINETIC energy; WAVE energy; SYNTHETIC aperture radar; OCEAN; TIDAL power; OCEAN energy resources; FORCED migration
- Publication
Journal of Geophysical Research. Oceans, 2023, Vol 128, Issue 12, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2023JC019913