The Response of the Southern Ocean to Sudden and Persistent Extreme SAM Forcing

One of the most obvious trends in Earth's changing climate is the steady increase in the Southern Annular Mode (SAM) index over the past few decades. Associated with this SAM increase is a strengthening and poleward shift of the prevailing westerlies blowing over the Southern Ocean. The Southern Ocean is known to be sensitive to changes in the overlying winds, however our understanding of the specific dynamics that couple the Southern Ocean and wind forcing is far from complete. Here we investigate the response of the Southern Ocean to sudden and persistent extreme SAM forcing conditions. We employ a global ocean-sea ice model, ACCESS-OM2, at a range of horizontal resolutions; 1, 1/4 and 1/10 degree. The coarser resolution simulations provide insight into the sensitivities of the response to the control and perturbation forcings, as well as the timescales of adjustment and magnitudes and locations of the responses; these simulations demonstrate the response is robust to control and perturbation forcing conditions. The high-resolution simulations are used to examine the eddy response to wind changes, including its timescale of adjustment, and the Southern Ocean heat and momentum uptake.