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Abstract Oceanic mixing, mostly driven by the breaking of internal waves at small scales in the ocean interior, is of major importance for ocean circulation and the ocean response to future climate scenarios. Understanding how internal waves transfer their energy to smaller scales from their generation to their dissipation is therefore an important step for improving the representation of ocean mixing in climate models. In this study, the processes leading to cross-scale energy fluxes in the internal wave field are quantified using an original decomposition approach in a realistic numerical simulation of the California Current. We quantify the relative contribution of eddy–internal wave interactions and wave–wave interactions to these fluxes and show that eddy–internal wave interactions are more efficient than wave–wave interactions in the formation of the internal wave continuum spectrum. Carrying out twin numerical simulations, where we successively activate or deactivate one of the main internal wave forcing, we also show that eddy–near-inertial internal wave interactions are more efficient in the cross-scale energy transfer than eddy–tidal internal wave interactions. This results in the dissipation being dominated by the near-inertial internal waves over tidal internal waves. A companion study focuses on the role of stimulated cascade on the energy and enstrophy fluxes.
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A Multiagency Experiment on Internal Wave Energy, Mixing, and Interactions and Their Representation in Global Ocean Models and Operational Forecasts
Abstract As part of a National Oceanographic Partnership Program (NOPP) project, seven teams—comprising investigators from universities, federal laboratories, and industry—are collaboratively investigating the generation, propagation, and dissipation of internal waves in the global ocean using complementary, state-of-the-art observations and model simulations. Internal waves, generated by the interaction of tides, winds, and mean flows, permeate the ocean and influence its physical state. Internal waves transport scalar and vector properties—both geographically and across scales—and contribute to irreversible mixing, modulate acoustic propagation, and complicate the identification of subinertial (e.g., geostrophic) flows in observations. For these reasons, accurately representing internal waves in global ocean forecast models is a high priority. The collaborations reported here are improving the understanding of the internal wave life cycle and enhancing model skill in simulating it. Three observational teams are collecting in situ data using 1) redeployable moored arrays that resolve internal waves from multiple directions, 2) global deployments of profiling floats that measure internal wave energy fluxes, shear, and mixing, and 3) high-resolution arrays that focus on bottom boundary layer processes. Four modeling teams are guiding the design and placement of these observation platforms and are using the collected observations to 1) improve internal wave representation and dissipation in ocean models, 2) conduct high-resolution process studies, and 3) implement data assimilation in idealized, regional, and global simulations. These efforts are further supported by high-resolution sea surface height measurements from the new Surface Water and Ocean Topography (SWOT) satellite, which provide context for in situ observations and improve ocean forecasting systems. Significance StatementA collaboration among scientists from U.S. universities, national laboratories, and industry is advancing our understanding and prediction of internal waves in the global ocean. These waves—characterized by vertical scales of tens to hundreds of meters and horizontal scales of tens to hundreds of kilometers—play a critical role in maritime commerce, naval operations, and ocean circulation. The team integrates novel observational approaches, including internal wave–resolving moored arrays, ship-of-opportunity float deployments, bottom boundary layer–distributed sensor networks, and satellite wide-swath altimetry, with cutting-edge global, regional, and process-model simulations. Together, these efforts are improving the representation of internal wave processes in ocean models and enhancing their predictive capabilities for operational forecasts.
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- Award ID(s):
- 2232796
- PAR ID:
- 10661057
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Editor(s):
- McPhaden, Michael
- Publisher / Repository:
- Americal Meteorological Society
- Date Published:
- Journal Name:
- Bulletin of the American Meteorological Society
- Volume:
- 107
- Issue:
- 1
- ISSN:
- 0003-0007
- Page Range / eLocation ID:
- E158 to E182
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Motivated by the importance of mixing arising from dissipating internal waves (IWs), vertical profiles of internal‐wave dissipation from a high‐resolution regional ocean model are compared with finestructure estimates made from observations. A horizontal viscosity scheme restricted to only act on horizontally rotational modes (such as eddies) is introduced and tested. At lower resolutions with horizontal grid spacings of 2 km, the modeled IW dissipation from numerical model agrees reasonably well with observations in some cases when the restricted form of horizontal viscosity is used. This suggests the possibility that if restricted forms of horizontal viscosity are adopted by global models with similar resolutions, they could be used to diagnose and map IW dissipation distributions. At higher resolutions with horizontal grid spacings of ∼250 m, the dissipation from vertical shear and horizontal viscosity act much more strongly resulting in dissipation overestimates; however, the vertical‐shear dissipation itself is found to agree well with observations.more » « less
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Abstract We provide a first-principles analysis of the energy fluxes in the oceanic internal wave field. The resulting formula is remarkably similar to the renowned phenomenological formula for the turbulent dissipation rate in the ocean, which is known as the finescale parameterization. The prediction is based on the wave turbulence theory of internal gravity waves and on a new methodology devised for the computation of the associated energy fluxes. In the standard spectral representation of the wave energy density, in the two-dimensional vertical wavenumber–frequency ( m – ω ) domain, the energy fluxes associated with the steady state are found to be directed downscale in both coordinates, closely matching the finescale parameterization formula in functional form and in magnitude. These energy transfers are composed of a “local” and a “scale-separated” contributions; while the former is quantified numerically, the latter is dominated by the induced diffusion process and is amenable to analytical treatment. Contrary to previous results indicating an inverse energy cascade from high frequency to low, at odds with observations, our analysis of all nonzero coefficients of the diffusion tensor predicts a direct energy cascade. Moreover, by the same analysis fundamental spectra that had been deemed “no-flux” solutions are reinstated to the status of “constant-downscale-flux” solutions. This is consequential for an understanding of energy fluxes, sources, and sinks that fits in the observational paradigm of the finescale parameterization, solving at once two long-standing paradoxes that had earned the name of “oceanic ultraviolet catastrophe.” Significance Statement The global circulation models cannot resolve the scales of the oceanic internal waves. The finescale parameterization of turbulent dissipation, a formula grounded in observations, is the standard tool by which the energy transfers due to internal waves are incorporated in the global models. Here, we provide an interpretation of this parameterization formula building on the first-principles statistical theory describing energy transfers between waves at different scales. Our result is in agreement with the finescale parameterization and points out a large contribution to the energy fluxes due to a type of wave interactions (local) usually disregarded. Moreover, the theory on which the traditional understanding of the parameterization is mainly built, a “diffusion approximation,” is known to be partly in contradiction with observations. We put forward a solution to this problem, visualized by means of “streamlines” that improve the intuition of the direction of the energy cascade.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1175/BAMS-D-24-0174.1
