Connecting flow-topography interactions, vorticity balance, baroclinic instability and transport in the Southern Ocean: the case of an idealized storm track

• Main Authors: Jouanno, Julien, Capet, Xavier
• Format: Text
• Language: English
• Published: 2020
• Subjects: Antarctic; Southern Ocean; The Antarctic; Antarc*; antartic*
• Online Access: https://doi.org/10.5194/os-2020-4; https://os.copernicus.org/preprints/os-2020-4/

The dynamical balance of the Antarctic circumpolar current and their implications on the functioning of the world ocean are not fully understood and poorly represented in global circulation models. In this study, the sensitivities of an idealized Southern Ocean (SO) storm track are explored with a set of eddy-rich numerical simulations. The classical partition between barotropic and baroclinic modes is sensitive to current-topography interactions in the mesoscale range 10–100 km, as comparisons between simulations with rough or smooth bathymetry reveal. Configurations with a rough bottom have weak barotropic motions, no wind-driven gyre in the lee of topographic ridges, less efficient baroclinic turbulence, and thus larger circumpolar transport rates. The difference in circumpolar transport depends on the strength with which (external) thermohaline forcings by the rest of the world ocean constrain the stratification at the northern edge of the SO. The study highlights the need for a comprehensive treatment of the Antartic Circumpolar Current (ACC) interactions with the ocean floor. It also sheds some light on the behavior of idealized storm tracks recently modelled: i) the saturation mechanism, whereby the circumpolar transport does not depend on wind intensity, is a robust and generic attribute of ACC-like circumpolar flows ii) the adjustment toward saturation can take place over widely different time scales (from months to years) depending on the possibility (or not) for barotropic Rossby waves to propagate signals of wind change and accelerate/decelerate SO wind-driven gyres. The real SO with a typical ACC saturation time scale of 2–3 years seems to lie in the “rough bottom/no wind-driven gyre” regime.