The Multi‐Scale Response of the Eddy Kinetic Energy and Transport to Strengthened Westerlies in an Idealized Antarctic Circumpolar Current.

The Southern Ocean's eddy response to changing climate remains unclear, with observations suggesting non‐monotonic changes in eddy kinetic energy (EKE) across scales. Here simulations reappear that smaller‐mesoscale EKE is suppressed while larger‐mesoscale EKE increases with strengthened winds. This change was linked to scale‐wise changes in the kinetic energy cycle, where a sensitive balance between the dominant mesoscale energy sinks—inverse KE cascade, and source—baroclinic energization. Such balance induced a strong (weak) mesoscale suppression in the flat (ridge) channel. Mechanistically, this mesoscale suppression is attributed to stronger zonal jets weakening smaller mesoscale eddies and promoting larger‐scale waves. These EKE multiscale changes lead to multiscale changes in meridional and vertical eddy transport, which can be parameterized using a scale‐dependent diffusivity linked to the EKE spectrum. This multiscale eddy response may have significant implications for understanding and modeling the Southern Ocean eddy activity and transport under a changing climate. Plain Language Summary: The response of eddies in the Southern Ocean to climate change is not well understood. In this study, we used a channel model that simulates the effects of wind on eddies. We found that smaller eddies have less kinetic energy (KE) when the winds are stronger. On the other hand, larger‐scale eddies have more KE with stronger winds. Similar phenomena are also observed in the observations. By analyzing the eddy's KE budget, the interaction between different scales of eddies and the interaction between the eddies and mean flow are strengthened when the winds get stronger. This leads to a reduction of eddy KE at smaller mesoscale scales and an increase at larger scales. From the observational view, stronger winds weaken smaller eddies and promote larger waves. This change in eddy KE also affects how eddies meridionally transport materials and how eddy diffusivity varies at different scales. Smaller eddies transport materials less when their KE is weakened, while larger eddies become stronger in transporting materials. These findings determine how eddy diffusivity responds to the changed eddy KE at different scales. The multi‐scale response of eddies to wind has important implications for understanding the behavior of Southern Ocean eddies in a changing climate. Key Points: Larger eddies got stronger and smaller eddies got weaker as Southern Ocean westerlies strengthenedBoth flat and ridge channel simulations suggest that these changes may be linked to changes in the inverse energy cascadeThe corresponding changes in scale‐wise meridional and vertical transport are also non‐monotonic [ABSTRACT FROM AUTHOR]