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| Titel |
The impact of the subtropical South Atlantic SST on South American precipitation |
| VerfasserIn |
A. S. Taschetto, I. Wainer |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 26, no. 11 ; Nr. 26, no. 11 (2008-11-10), S.3457-3476 |
| Datensatznummer |
250016286
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| Publikation (Nr.) |
 copernicus.org/angeo-26-3457-2008.pdf |
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| Zusammenfassung |
The Community Climate Model (CCM3) from the National Center for Atmospheric
Research (NCAR) is used to investigate the effect of the South Atlantic sea
surface temperature (SST) anomalies on interannual to decadal variability of
South American precipitation. Two ensembles composed of multidecadal
simulations forced with monthly SST data from the Hadley Centre for the
period 1949 to 2001 are analysed.
A statistical treatment based on signal-to-noise ratio and Empirical
Orthogonal Functions (EOF) is applied to the ensembles in order to reduce
the internal variability among the integrations. The ensemble treatment
shows a spatial and temporal dependence of reproducibility. High degree of
reproducibility is found in the tropics while the extratropics is apparently
less reproducible. Austral autumn (MAM) and spring (SON) precipitation
appears to be more reproducible over the South America-South Atlantic
region than the summer (DJF) and winter (JJA) rainfall. While the
Inter-tropical Convergence Zone (ITCZ) region is dominated by external
variance, the South Atlantic Convergence Zone (SACZ) over South America is
predominantly determined by internal variance, which makes it a difficult
phenomenon to predict. Alternatively, the SACZ over western South Atlantic
appears to be more sensitive to the subtropical SST anomalies than over the
continent.
An attempt is made to separate the atmospheric response forced by the South
Atlantic SST anomalies from that associated with the El Niño – Southern
Oscillation (ENSO). Results show that both the South Atlantic and Pacific
SSTs modulate the intensity and position of the SACZ during DJF.
Particularly, the subtropical South Atlantic SSTs are more important than
ENSO in determining the position of the SACZ over the southeast Brazilian
coast during DJF. On the other hand, the ENSO signal seems to influence the
intensity of the SACZ not only in DJF but especially its oceanic branch
during MAM. Both local and remote influences, however, are confounded by the
large internal variance in the region. During MAM and JJA, the South
Atlantic SST anomalies affect the magnitude and the meridional displacement
of the ITCZ. In JJA, the ENSO has relatively little influence on the
interannual variability of the simulated rainfall. During SON, however, the
ENSO seems to counteract the effect of the subtropical South Atlantic SST
variations on convection over South America. |
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