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| Titel |
Links between the Southern Annular Mode and the Atlantic Meridional Overturning in a climate model |
| VerfasserIn |
Camille Marini, Claude Frankignoul, Juliette Mignot |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033538
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| Zusammenfassung |
| The links between the atmospheric Southern Annular Mode (SAM), the Southern Ocean
and the Atlantic Meridional Overturning Circulation (AMOC) at interannual to
multidecadal timescales are investigated in a 500-years control integration of the
IPSL-CM4 climate model. The Antarctic Circumpolar Current is well correlated with the
SAM at the yearly timescale, reflecting that an intensification of the Westerlies
south of 45-S leads to its intensification. At the same time, the global Meridional
Overturning Circulation is modified locally, primarily reflecting a forced barotropic
response.
In the model, a positive SAM phase is found to precede an AMOC acceleration by about
8 years. This is due to an atmospheric teleconnection between the SAM and the northern
North Atlantic, which results from a hemispherically symmetric influence of El Niño
Southern Oscillation (ENSO). A SLP low centered near the tip of Greenland and a positive
SAM phase are indeed found during La Niña conditions, leading to anomalous salinity
advection toward the main area of deep convection in the model. This leads to a progressive
erosion of the vertical stratification, which enhances the deep convection and then
accelerates the AMOC. The observations also suggest interhemispheric links related to
ENSO, albeit less pronounced in the northern North Atlantic, and even though no
significant correlations are found between the SAM and the North Atlantic SLP in the
reanalysis.
A more direct but slower oceanic link between the SAM and the AMOC is found at
multidecadal time scale. Salinity anomalies generated by the SAM both in the Pacific and in
the Indian basins enter the South Atlantic and propagate northward. They eventually reach the
northern North Atlantic about 70 years after a positive SAM, where they similarly affect the
vertical stratification and thus the AMOC. A deceleration of the AMOC is found 20 years
later. This phase reversal is due to the same mechanism as negative salinity anomalies coming
from the Indian and Pacific basin enter in the Atlantic basin about 20 years after a positive
SAM phase. This freshening is generated earlier by SAM-driven anomalous advection
in the Pacific and the Indian basins, and is then advected into the Atlantic basin. |
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