A Numerical Case Study of the Impact of Submesoscale Feedbacks on Mesoscale Eddies

Yunlong Fei, Shaoqing Zhang*, Wei Zhao*, Gang Li, Kaidi Wang and Yangyang Yu

Understanding the impact of feedback of submesoscales on mesoscale eddies is critical to clarify the multiscale interactions in the ocean, yet it remains ambiguous. This study first designs a “twin” downscaled framework with two-way nesting that can control the feedback strength of submesoscales resolved by a 1km resolution simulation to the 3km resolution mesoscale-resolved simulation. A mesoscale dipole of cold-warm eddies in the northwest Pacific Subtropical Countercurrent area appears in the two-way downscaled simulation, but the dipole structure doesn’t sustain in the absence of submesoscale feedback to mesoscale eddies. When submesoscales provide feedback to the mesoscale eddies, the cyclonic eddy in the dipole becomes less susceptible to stretching, confirming the significance of submesoscales in regulating mesoscale eddies. Then, the underlying dynamical mechanisms are thoroughly examined from the perspectives of spectral analysis and scale kinetic energy flux with different feedback strengths. The frequency-wavenumber spectra of kinetic energy (KE) reveal a remarkable enhancement when submesoscales provide feedback to the mesoscale eddies, highlighting the importance of submesoscale feedback on mesoscale eddies. Although submesoscales are mainly concentrated within the upper ocean, the frequency-wavenumber spectra of normalized vertical relative vorticity and horizontal divergence are significantly improved at a depth of 200m. In terms of scale kinetic energy flux, the inverse cascade of KE can extend to smaller scales when submesoscales provide feedback to mesoscale eddies. This indicates that mesoscale eddies can be strengthened when more submesoscales are resolved, further influencing the shape of the cyclonic eddy in this case. Nevertheless, the energy levels and scale kinetic energy fluxes are insensitive to the feedback strength; both of them with different feedback strengths exhibit nearly the same magnitudes. This finding can help us get a deep understanding of multiscale interactions between mesoscale eddies and submesoscales.

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Published on: May 22, 2026 Pages: 9-23

Full Text PDF Full Text HTML DOI: 10.17352/ams.000052
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