An assessment of Southern Ocean water masses and sea ice during 1988–2007 in a suite of interannual CORE-II simulationsстатья
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Аннотация:In the framework of the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II), we
present an analysis of the representation of the Antarctic Circumpolar Current (ACC) and Southern Ocean Meridional Overturning Circulation (MOC) in a suite of sixteen global ocean-sea ice models. We focus on the mean, variability and trends of both the ACC and MOC over the 1958–2007 period, and discuss their relationship with the surface forcing. Most models show weak ACC sensitivity to changes in forcing during the past five decades, and they can be considered to be in an eddy saturated regime. Larger contrasts arise when considering MOC trends, with a majority of models exhibiting significant strengthening of the MOC. Only a few models show a reduced sensitivity to forcing changes, responding with an intensified eddy-induced circulation and providing some degree of eddy compensation, although still manifesting considerable decadal trends. Both ACC and MOC interannual variability are largely controlled by the Southern Annular Mode (SAM). Based on these results, models are clustered into two groups. Models with constant or two-dimensional specification of the eddy-induced advection coecient show larger ocean interior decadal trends, higher correlation with the SAM, larger ACC decadal trends and no eddycompensation in the MOC. Eddy-permitting or models with a three-dimensional time varying show lower correlation with the SAM, smaller changes in isopycnal slopes and associated ACC trends and signs of eddy compensation. As previously argued, a constant in time or space is responsible for a poor representation of mesoscale eddy eects and cannot properly simulate the sensitivity of the ACC and MOC to changing surface forcing. Evidence is given for a larger sensitivity of the MOC as compared to the ACC, even when approaching eddy saturation. Surface forcing changes experienced during years 1948–2007 are weaker than what was previously used for testing ocean models and their mesoscale parameterizations with idealised forcing anomalies. Future process studies designed for disentangling the role of momentum and buoyancy forcing in driving the ACC and MOC are proposed.