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Southern Boundaries in Global Ocean Models: Can We Do Better?

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Schodlok, M. , Losch, M. and Wenzel, M. (2006): Southern Boundaries in Global Ocean Models: Can We Do Better? , AGU Fall Meeting, San Francisco, USA, Dec 11-15 .
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Abstract:

Dense water masses form on the continental shelves around Antarctica, sink,and spread as a ma jor contributor to the overturning circulation into theglobal abyss. Global ocean circulation models often do not adequately re-solve high latitude processes due to, for example, a poor representation ofthe continental shelves and an insufficient spatial resolution. Without theseprocesses which are important for the lower part of the global overturningcirculation, the characteristics and flow of deep and bottom waters often re-main unrealistic in these models. We present two approaches to treat thesouthern boundary in global ocean models and in turn improve the hydrog-raphy of the Southern Ocean, the Antarctic Circumpolar Current and theglobal circulation in those models. First, a modified Large Scale GeostrophicModel (LSG) with global data assimilation and an integration time scaleof 13 years is constrained further by hydrographic sections in the Ross andWeddell seas. These sections are obtained from an accurate regional model.Secondly, in a long (3000 years) forward integration, a global 2 degree general cir-culation model takes into account high latitude processes by restoring thesouthern boundaries at 76S in the Ross and Weddell seas to hydrographyand velocity values from the same regional model. Sensitivity experimentswith both model configurations shed light on the influence of the additionaldata in the individual basins (Ross and Weddell Sea) on a regional andglobal scale. The Weddell Sea circulation significantly affects the course ofthe Antarctic Circumpolar Current with consequences for Southern Oceanwater mass characteristics and the spreading of deep and bottom waters inthe South Atlantic. Regional changes in the Pacific sector of the SouthernOcean can be attributed to the additional data in the Ross Sea. In spiteof different physics, time scales of integration, and methods of incorporatingthe regional model data between the two global models, the effects of theadditional information are consistent in both global models.

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