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Response of the South and Tropical Atlantic to changes in the Meridional Overturning Circulation in numerical experiments with the SPEEDO (MICOM-SPEEDY) coupled model
E. Campos, R. Haarsma, W. Hazeleger, C. Severijns and S. Drijfout
University of Sao Paulo
(Abstract received 05/08/2007 for session X)
ABSTRACT
The northward ocean heat transport in the Atlantic is dominated by a basin-wide meridional overturning circulation (MOC). The inflow of MOC water into the tropical Atlantic occurs via the South Equatorial Current and the North Brazil Current. Some of that water upwells into the surface layer, potentially affecting coupled ocean-atmosphere variability. Tropical Atlantic Variability is dominated by a zonal equatorial mode and an interhemispheric mode. Climate models generally simulate that greenhouse warming induces a reduction of the MOC, resulting in a colder North Atlantic and a warmer Tropical and South Atlantic. In this work we explore the impacts of changes in the MOC due to (a) a total collapse of the Thermohaline Circulation and (b) the interruption of the Agulhas leakage into the South Atlantic. In this experiments we use the coupled SPEEDO model, which simulates realistically the equatorial thermocline and the tropical Atlantic variability. In the experiment in which the inflow of the MOC into the Atlantic basin is totally reduced (NO-THC), the well-known interhemispheric gradient in surface temperature develops and the ITCZ shifts southward. These changes are characteristic of the Atlantic Meridional Oscillation. Also, upwelling on the equator reduces and characteristics of Tropical Atlantic Variability change. In particular, a deeper equatorial thermocline causes the zonal mode of interannual variability to reduce and Benguela Nino\'s to become more pronounced. In the experiment with the no Agulhas leakage (NO-AGU), the resulting fresh and cold anomaly reaches the eastern Equatorial region in the undercurrent. There, instead of surfacing, the anomaly spread northward within the thermocline and eventually reaches the Guinea Dome. The Tropical Atlantic modes of variability are not affected in this experiment.
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2007 LOM Workshop, Bergen, Norway, August 20-22, 2007