Decadal variability of the Antarctic Circumpolar Current in an idealized chaotic ocean–atmosphere coupled model

An idealized ocean-atmosphere coupled model exhibiting chaotic behaviour is developed to represent the dynamics of the Antarctic Circumpolar Current, one of the most intense ocean currents on Earth. On a meridional-depth plane, the model is driven by the competition between eddy-induced advection and wind-induced advection, where a feedback of meridional ocean temperature contrast on the wind intensity is allowed. Along the zonal direction, the lattice of individual meridional-depth dynamics are zonally coupled through zonal turbulent diffusivity. We show that ocean-atmosphere coupling is crucial to set the chaotic dynamics, whereas the zonal turbulent diffusivity is crucial for setting a realistic intensity of the Antarctic Circumpolar Current. For a value of zonal turbulent diffusivity between 200 and 10 000 m 2 s −1 the zonal mean transport is 121 Sv (1 Sv ≡ 1 0 6 m 3 s −1 ) and exhibits a main spectral signature at 8.1 years. The diffusivity coefficient controls the level of zonal synchronicity of the Antarctic Circumpolar Current going from a fully zonally-independent system to a fully synchronized lattice with no zonal variation. The realistic regime corresponds to an intermediate level of synchronicity, where the footprint length scale measured the zonal distance over which local meridional-depth dynamics are impacting each other. This zonal length scale footprint is set by the competition between the zonal turbulent diffusivity, zonally coupling the dynamics, and the extreme event ( > 82 percentile) return period ( ∼ 48.5 years), resetting the local meridional-depth dynamics.