Stabilization of thermohaline circulation by wind-driven and vertical diffusive salt transport |
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Authors: | A Oka H Hasumi N Suginohara |
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Institution: | (1) Center for Climate System Research, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan E-mail: akira@ccsr.u-tokyo.ac.jp, JP |
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Abstract: | The stability of the thermohaline circulation is investigated using an ocean general circulation model coupled to a simple
atmospheric model. The atmospheric model is so developed that it represents the wind stress and the freshwater flux more realistically
than existing energy balance models. The coupled model can reproduce the realistic deep ocean circulation without any flux
adjustment. Effects of the wind stress and the vertical diffusion on the thermohaline circulation are studied by conducting
various experiments with the coupled model. The Ekman upwelling between 60∘N and 90∘N brings up salt to the sea surface, while the compensation flow of the Ekman transport and the wind-driven gyre circulation
between 30∘N and 60∘N carry salt horizontally to the high latitudes. By carrying out experiments where the wind stress is completely or partly
removed, it is demonstrated that either of the vertical or the horizontal salt transport prevents the halocline formation
at high latitudes and maintains the thermohaline circulation. For an experiment in which the vertical diffusivity is enhanced
at high latitudes, it is shown that the vertical diffusion at high latitudes also prevents the halocline formation and stabilizes
the thermohaline circulation. It is also shown that the value of the vertical diffusivity at high latitude affects the existence
of the multiple equilibria of the thermohaline circulation.
Received: 26 April 2000 / Accepted: 10 January 2001 |
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