A frictional control mechanism of circumpolar transport in barotropic reentrant channel models

Recent studies have reported that an increase in the bottom drag coefficient can enhance the volume transport of the Antarctic Circumpolar Current. Several mechanisms have been proposed to explain this frictional control, including the regulation of the geostrophic velocity by baroclinic instability and the influence of the form stress associated with standing meanders and wind-driven gyres. In this study, the role of momentum transport associated with Rossby wave radiations from disturbances is investigated as a potential frictional control mechanism. To highlight roles of the Rossby wave radiation, numerical experiments are conducted using barotropic reentrant channel models with topographic obstacles. In the high-drag regime, the circumpolar component is wind-driven, and the imbalance between the westerlies and topographic form stress sustains a net eastward transport. In contrast, in the low-drag regime, the eddy-driven westward circumpolar current is formed. In this case, the eastward flow at the center of the double gyre becomes unstable to barotropic instability. Analyses of the wave activity flux and momentum budget indicate that the Rossby wave transports westward momentum both northward and southward from the unstable region, which is responsible for the westward circumpolar current formation and maintenance. Although the direct application of the barotropic channel model to oceans requires caution, our findings imply that Rossby wave radiations from jets may play a role in the frictional control of the Antarctic Circumpolar Current.