Low-frequency variability in the Southern Ocean region in a simplified coupled model
[1] 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...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.565.762 http://gershwin.ens.fr/dandrea/mazetal.pdf |
| Summary: | [1] 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 timescales. 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 sea surface temperature (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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