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Low-frequency variability in the Southern Ocean region in a simplified coupled model

G. Maze, F. D’Andrea and A. Colin de Verdière, 2006
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, C05010, doi:10.1029/2005JC003181, 2006

Access online at http://dx.doi.org/10.1029/2005JC003181 or download at the bottom of this page.

Abstract:
Patterns of interannual variability of the ocean-atmosphere coupled system in the Southern Hemisphere extratropics are studied with a simple dynamical model, in order to determine the basic physical processes of interaction independently of tropical forcing. The model used is an atmospheric quasi-geostrophic model coupled to a “slab” oceanic mixed layer, which includes mean geostrophic advection by the Antarctic Circumpolar Current (ACC). The ocean-atmosphere coupling occurs through surface heat fluxes and Ekman current heat advection. In a fully coupled simulation, the atmospheric part of the model, which includes high frequency transient eddies at midlatitudes, exhibits a strong Southern Annular Mode (SAM) as the first mode of variability at interannual time-scales. The SAM-related wind anomalies induce Ekman currents in the mixed layer which produce sea surface temperature anomalies. These are then advected along by the ACC. A forced mechanism where the ocean role is reduced to advect the SST appears sufficient to reproduce the main features of the variability. Nevertheless, a positive feedback of the ocean was also found. It operates through anomalous Ekman currents heat advection and contributes to the maintenance of the SST anomaly.


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G. Maze (admin),
Nov 4, 2008, 2:32 PM
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