A Numerical Case Study of the Impact of Submesoscales Feedback on Mesoscale Eddies

This study designs a two-way downscaled framework that controls the feedback strength of submesoscales resolved by 1km resolution simulation to the 3km resolution mesoscale-resolved simulation. A mesoscale dipole with cold-warm eddies is observed in the simulation, but the dipole structure can’t be maintained without submesoscales feedback. When submesoscales feedback is allowed, the cyclonic eddy in the dipole becomes less susceptible to stretching. Then, the underlying dynamical mechanisms are thoroughly examined from the perspectives of spectral analysis and scale kinetic energy (KE) flux in five experiments with different feedback strength. The wavenumber and frequency-wavenumber spectra of KE show a significant improvement when submesoscales feedback is permitted, confirming the significance of submesoscales feedback in sustaining mesoscale eddies. Although submesoscales are mainly concentrated within the upper ocean, their influence can extend down to 200m underwater. The frequency-wavenumber spectra of normalized vertical relative vorticity and horizontal divergence further confirm those conclusions. Regarding the scale KE flux, the inverse cascade can extend to smaller scales accompanied by increased strength as submesoscales feedback is allowed. This suggests that the mesoscale eddies can be strengthened by submesoscales to make it more coherent and not quickly be dissipated. This finding helps deepen our understanding of multiscale interactions between mesoscales and submesoscales.