[A-CG36] Dynamics of Oceanic and Atmospheric Waves, Vortices, and Circulations

[ACG36-01] A theory of standing meanders of the Antarctic Circumpolar Current and their response to wind

★Invited Papers

*Maxim Nikurashin^1,2 (1.Institute for Marine and Antarctic Studies, University of Tasmania, 2.Australian Antarctic Program Partnership, University of Tasmania, Hobart, Tasmania)

Keywords:Antarctic Circumpolar Current, meanders, sensitivity to wind, Rossby waves

Standing meanders of the Antarctic Circumpolar Current (ACC) and associated eddy hotspots play an important role for the meridional heat flux, downward momentum transfer, ocean ventilation, and the response of the ACC to wind. Previous modelling studies show that the vorticity balance characterising standing meanders in the upper ocean is dominated by advection of relative vorticity and stretching (horizontal divergence). The adjustment of this vorticity balance has been suggested to provide a pathway for the transfer of the wind momentum input from the surface to the bottom, leading to stronger bottom flows and energy dissipation. Using a quasi-geostrophic theory combined with a regional model of the Macquarie Ridge region and an idealized channel model, we explore the dynamics and vertical structure of standing meanders of the ACC. The results show that the entire vertical structure of the meander, including its dynamics in the upper ocean, is maintained by the bottom flow interacting with topography. The strong mean shear of the ACC aloft leads to the change of the Rossby wave radiation regime within the water column and, as a result, to the dominance of advection of relative vorticity and stretching in the upper ocean. The amplitude of the meander, and hence its curvature and vorticity balance, in the upper ocean are sensitive to changes in the bottom flow. Our results suggest an important role played by the barotropic flow component for regulating the response of the Southern Ocean dynamics to changes in wind.