Topographic Modulation of the Wind Stress Impact on Eddy Activity in the Southern Ocean.

Previous studies proposed that the increase in the eddy kinetic energy (EKE) in the Southern Ocean in recent decades is primarily caused by the strengthening of circumpolar surface westerlies. However, the spatial pattern of EKE change does not match the pattern of wind change. Here, we revisit the relationship between EKE and wind stress through an observational analysis and model experiments and show that the change in EKE is primarily determined by the mean flow. The increasing wind stress intensifies the circumpolar mean flow contributing to increasing EKE; yet strong EKE variations are generally confined downstream of major topographic features. This arises from the releasing of available potential energy as the mean flow passes through the topography. Our results indicate that the change in Southern Ocean eddy activity has a distinct localization characteristic due to the strong dynamical influence of topography. Plain Language Summary: Eddy kinetic energy has been increasing in the Southern Ocean over the past few decades. These changes in the eddy field are of great importance because they play a crucial role in modulating the ocean circulation response to surface forcing. However, the eddy kinetic energy (EKE) changes are inhomogeneous in the Southern Ocean. To understand the pattern of these changes, we analyze the satellite altimeter record over a period of 28 years since 1993 and carry out a set of idealized simulations. We find that the change of EKE is more related to the mean flow than to localized wind changes. The increasing wind stress contributes to increasing EKE by intensifying the circumpolar mean flow with local wind stress playing a minor role in the pattern of EKE changes. Strong EKE variations are generally confined downstream of major topographic features, suggesting strong modulation by topography. This study indicates the change of EKE depends on the combination of wind stress, mean flow, and topography in the Southern Ocean. Key Points: Eddy activity patterns are primarily determined by Southern Ocean topographic featuresLocal wind stress plays a minor role in modulating the pattern of eddy activityWind stress intensifies mean flow and topography sets locations of conversion to eddy activity [ABSTRACT FROM AUTHOR]