Impact of the Southern ocean winds on sea-ice - ocean interaction and its associated global ocean circulation in a warming world
Cheon, Woo Geunn
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This dissertation discusses a linkage between the Southern Ocean (SO) winds and the global ocean circulation in the framework of a coarse-resolution global ocean general circulation model coupled to a sea-ice model. In addition to reexamination of the conventional linkage that begins with northward Ekman transport and extends to the North Atlantic (NA) overturning, the author investigates a new linkage that begins with the Southern Hemisphere (SH) sea-ice ? ocean interaction perturbed by the anomalous SO winds and extends to the SH overturning, the response of the NA overturning, and the long-term baroclinic adjustment of the Antarctic Circumpolar Current (ACC). How the above two linkages will interact with each other in a warming world is also investigated. An interactive momentum flux forcing, allowing for the strength of momentum flux between atmosphere and sea ice to vary in response to the simulated sea-ice conditions, enhances wind-driven ice divergence to increase the fraction of leads and polynyas, which increases dense water formation, and thus intensifies convection. Within three experimental frameworks, this increased dense water consistently increases the Antarctic Bottom Water formation, which directly intensifies the SH overturning and indirectly weakens the NA overturning. As a result of the hemispheric change in overturning circulations, the meridional density gradient across the ACC appears to increase, ultimately increasing the baroclinic part of the ACC via an enhanced thermal wind shear. Subsequently, impacts of the poleward shifted and intensified SH subpolar westerly winds (SWWs) on the global ocean circulation are investigated in phases. When the SWWs are only shifted poleward, the effect of the anomalous winds is transmitted to the northern NA, decreasing both the NA overturning and the North Atlantic Deep Water (NADW) outflow. However, when the SWWs are shifted poleward and intensified, this effect is cut off by the intensified Deacon cell overturning, and is not transmitted to the northern NA, and instead increases the NADW outflow substantially. To sum up, with respect to the SO winds perturbed by the global warming, the SH overturning cell and the NADW outflow increase, leading to an increase in the volume transport of the ACC.
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