The impact of topography and eddy parameterization on the simulated southern ocean circulation response to changes in surface wind stress

Abstract

It remains uncertain how the Southern Ocean circulation responds to changes in surface wind stress, and whether coarse-resolution simulations, where mesoscale eddy fluxes are parameterized, can adequately capture the response. We address this problem using two idealized model setups mimicking the Southern Ocean: A flat-bottom channel and a channel with moderately complex topography. Under each topographic configuration and varying wind stress, we compare several coarse-resolution simulations, configured with different eddy parameterizations, against an eddy-resolving simulation. We find that 1) without topography, sensitivity of the Antarctic Circumpolar Current (ACC) to wind stress is overestimated by coarse-resolution simulations, due to an underestimate of the sensitivity of the eddy diffusivity; 2) in the presence of topography, stationary eddies dominate over transient eddies in counteracting the direct response of the ACC and overturning circulation to wind stress changes; and 3) coarse-resolution simulations with parameterized eddies capture this counteracting effect reasonably well, largely due to their ability to resolve stationary eddies. Our results highlight the importance of topography in modulating the response of the Southern Ocean circulation to changes in surface wind stress. The interaction between mesoscale eddies and stationary meanders induced by topography requires more attention in future development and testing of eddy parameterizations.