Abstract: A strong nearly zonal Antarctic Circumpolar Current (ACC), combined with complex fronts, dominates the circulation system in the Southern Ocean. In this study, historical surface drifter observations collected from the Southern Ocean were used to study the near-surface structure, variability, and energy characteristics of the ACC. Standard variance ellipses indicated that both the Agulhas Return Current and the East Australian Warm Current are stable supplements of the near-surface ACC. During austral winter, current velocity increases because of the enhanced westerly wind. Stimulated by the meridional motion of the ACC, the meridional velocity shows greater characteristics of instability than the zonal velocity does over the core current. Additionally, the ACC exhibits an eastward declining trend in core current velocity from southern Africa. The energy distribution suggests that the mean kinetic energy (MKE), eddy kinetic energy (EKE), and  are strong over the core current of the ACC. However, EKE/MKE suggests there is much less (more) eddy dissipation in regions with strong (weak) energy distribution. All energy forms other than EKE/MKE present west–east reducing trends. Furthermore, eddy dissipation has much greater effect on MKE in the northern part of the Southern Ocean.

Key words: mean structure, energy characteristics, Antarctic Circumpolar Current, sea surface drifter