The role of meridional density differences for a wind-driven overturning circulation |
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| Authors: | J Schewe A Levermann |
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| Institution: | (1) Earth System Analysis, Potsdam Institute for Climate Impact Research, Telegrafenberg A62, 14473 Potsdam, Germany;(2) Physics Institute, Potsdam University, Potsdam, Germany |
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| Abstract: | Experiments with the coupled climate model CLIMBER-3α, which contains an oceanic general circulation model, show deep upwelling in the Southern Ocean to be proportional to
the surface wind stress in the latitudinal band of Drake Passage. At the same time, the distribution of the Southern Ocean
upwelling onto the oceanic basins is controlled by buoyancy distribution; the inflow into each basin being proportional to
the respective meridional density difference. We observe approximately the same constant of proportionality for all basins,
and demonstrate that it can be directly related to the flow geometry. For increased wind stress in the Southern Ocean, the
overturning increases both in the Atlantic and the Indo-Pacific basin. For strongly reduced wind stress, the circulation enters
a regime where Atlantic overturning is maintained through Pacific upwelling, in order to satisfy the transports set by the
density differences. Previous results on surface buoyancy and wind stress forcing, obtained with different models, are reproduced
within one model in order to distill a consistent picture. We propose that both Southern Ocean upwelling and meridional density
differences set up a system of conditions that determine the global meridional overturning circulation. |
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