Study Links Mesoscale Eddy-Internal Wave Coupling to Ocean Gyre Dynamics
A new theoretical and observational study finds that coupling between mesoscale ocean eddies and internal waves plays a dominant role in the energy budget of the Sargasso Sea and helps sustain large-scale potential vorticity gradients in ocean gyres. The work updates a 1976 theory by Müller, using a relaxation time scale approximation to balance eddy-induced wave perturbations with nonlinearity, and finds strong agreement with observational data. The findings have implications for understanding how gyre-scale ocean circulation patterns are maintained over time.
Researchers have developed and validated a prognostic formulation of triple coherence describing energy exchange between mesoscale eddies and the internal wavefield, comparing theoretical predictions against observations from the Sargasso Sea. The study builds on Müller's (1976) framework and finds remarkable agreement between the updated theory and data, supporting the hypothesis that eddy-wave coupling dominates the regional internal wave energy budget and sets the character of the internal wavefield in that region. The coupling also acts as an amplifier of tertiary energy inputs from larger vertical scales associated with internal swell. Energy extraction from eddies occurs at horizontal and vertical scales characteristic of baroclinic instability and potential vorticity fluxes. Extending the analysis to the Southern Recirculation Gyre of the Gulf Stream, the authors argue that the nonlinear relaxation mechanism provides local eddy enstrophy damping consistent with potential vorticity flux observations from the Local Dynamics Experiment. This places the end of the potential enstrophy cascade at the energy-containing scale of the internal wavefield in the spectral domain. The overarching conclusion is that mesoscale eddy–internal wave coupling is a key mechanism responsible for maintaining gyre-scale potential vorticity gradients.
What's missing
The authors acknowledge that the Southern Recirculation Gyre analysis is speculative, and it is unclear how well the Sargasso Sea findings generalize to other ocean basins or gyre systems. The degree to which the relaxation time scale approximation holds under varying oceanic conditions is not fully constrained.
What different sources said
- arXiv physicsCenter
Mesoscale Eddy -- Internal Wave Coupling. III. The End of the Enstrophy Cascade and Maintenance of Gyre Scale Potential Vorticity Gradients
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