Abstract
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 seventeen 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. We aim to quantify the degree of eddy saturation and eddy compensation in the models participating in CORE-II, and compare our results with available observations, previous fine-resolution numerical studies and theoretical constraints. Most models show weak ACC transport 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 during the late 20th and early 21st century. Only a few models show a relatively small sensitivity to forcing changes, responding with an intensified eddy-induced circulation that provides some degree of eddy compensation, while still showing considerable decadal trends. Both ACC and MOC interannual variabilities 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 (horizontal) specification of the eddy-induced advection coefficient κ show larger ocean interior decadal trends, larger ACC transport decadal trends and no eddy compensation in the MOC. Eddy-permitting models or models with a three-dimensional time varying κ show smaller changes in isopycnal slopes and associated ACC trends, and partial eddy compensation. As previously argued, a constant in time or space κ is responsible for a poor representation of mesoscale eddy effects 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 transport, even when approaching eddy saturation. Future process studies designed for disentangling the role of momentum and buoyancy forcing in driving the ACC and MOC are proposed.
Original language | English |
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Pages (from-to) | 84-120 |
Number of pages | 37 |
Journal | Ocean Modelling |
Volume | 93 |
DOIs | |
Publication status | Published - 14 Sept 2015 |
Externally published | Yes |
Bibliographical note
Publisher Copyright:© 2015 Elsevier Ltd.
Funding
The ACCESS model is supported by the Australian Government Department of the Environment, the Bureau of Meteorology and CSIRO through the Australian Climate Change Science Programme. S. M. Downes was supported by the ARC Centre of Excellence for Climate System Science (grant CE110001028). AWI is a member of the Helmholtz Association of German Research Centers. Q. Wang and D. Sidorenko are funded by the Helmholtz Climate Initiative REKLIM (Regional Climate Change) project. The BERGEN contribution is supported by the Research Council of Norway through the EarthClim (207711/E10) and NOTUR/NorStore projects, as well as the Centre for Climate Dynamics at the Bjerknes Centre for Climate Research. The CMCC contribution received funding from the Italian Ministry of Education, University, and Research and the Italian Ministry of Environment, Land, and Sea under the GEMINA project. NCAR is sponsored by the U. S. National Science Foundation (NSF). The GEOMAR experiments were performed at the North-German Supercomputing Alliance (HLRN). L. Patara was financially supported by the Cluster of Excellence ‘The Future Ocean’ funded within the framework of the Excellence Initiative by the DFG. The INMOM model was sponsored by the Russian Science Foundation (project number 14-27-00126). S. G. Yeager was supported by the NOAA Climate Program Office under Climate Variability and Predictability Program Grant NA09OAR4310163 and NA130AR4310138 and by the NSF Collaborative Research EaSM2 grant OCE-1243015. We thank Carolina Dufour, Adele Morrison and Ivy Frenger for comments on earlier drafts. The authors would also like to thank the three anonymous reviewers for their insightful and constructive comments and suggestions on the manuscript.
Funders | Funder number |
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ARC Centre of Excellence for Climate System Science | CE110001028 |
Bureau of Meteorology | |
Helmholtz Climate Initiative REKLIM | |
Italian Ministry of Environment, Land | |
NOTUR | |
NorStore | |
National Science Foundation | |
National Oceanic and Atmospheric Administration | OCE-1243015, NA09OAR4310163, NA130AR4310138 |
Natural Environment Research Council | noc010010 |
Commonwealth Scientific and Industrial Research Organisation | |
Deutsche Forschungsgemeinschaft | |
Ministero dell’Istruzione, dell’Università e della Ricerca | |
Department of the Environment, Australian Government | |
Norges Forskningsråd | 207711/E10 |
Russian Science Foundation | 14-27-00126 |
Keywords
- Antarctic Circumpolar Current
- Global ocean-sea ice modeling
- Model comparisons
- Southern Ocean dynamics
- Southern Ocean meridional overturning circulation