Historical surface drifter observations collected from the Southern Ocean are used to study the near-surface structure,variability,and energy characteristics of the Antarctic Circumpolar Current(ACC).A strong,nearly zonal ACC combined with complex fronts dominates the circulation system in the Southern Ocean.Standard variance ellipses indicate that both the Agulhas Return Current and the East Australian Warm Current are stable supplements of the near-surface ACC,and that the anticyclonic gyre formed by the Brazil warm current and the Malvinas cold current is stable throughout the year.During austral winter,the current velocity increases because of the enhanced westerly wind.Aroused by the meridional motion of the ACC,the meridional velocity shows greater instability characteristics than the zonal velocity does over the core current.Additionally,the ACC exhibits an eastward declining trend in the core current velocity from southern Africa.The characteristics of the ACC are also argued from the perspective of energy.The energy distribution suggests that the mean kinetic energy(MKE),eddy kinetic energy(EKE),and EKE are strong over the core currents of the ACC.However,in contrast,EKE/MKE suggests there is much less(more)eddy dissipation in regions with strong(weak)energy distribution.Both meridional and zonal energy variations are studied to illustrate additional details of the ACC energy characteristics.Generally,all the energy forms except EKE/MKE present west-east reducing trends,which coincide with the velocity statistics.Eddy dissipation has a much greater effect on MKE in the northern part of the Southern Ocean.
