CR 68:257-276 (2016)  -  DOI: https://doi.org/10.3354/cr01354

La Niña events before and after 1979 and their impact in southeastern South America during austral summer: role of the Indian Ocean

Gabriel Cazes-Boezio1,*, Stefanie Talento1,2

1Universidad de la República, Instituto de Mecánica de los Fluidos e Ingeniería Ambiental, Facultad de Ingeniería, Julio Herrerra y Reissig 565, Montevideo, Uruguay
2Universidad de la República, Instituto de Física, Facultad de Ciencias, Iguá 4225, Montevideo, Uruguay
*Corresponding author:

ABSTRACT: In this study, we analyzed the influence of interannual variability in sea surface temperature (SST) on the climate of southeastern South America (SESA) during austral summer. We found that the correlation between the El Niño Southern Oscillation (ENSO) and rainfall over southern Brazil-northern Uruguay (SB-NU) was not statistically significant between 1949 and 1978, but it was significant between 1979 and 2009. The results show that this change in correlation was largely due to the modified rainfall response over SB-NU to La Niña events. A cluster analysis for all summers between 1949 and 2009 identified a turning point of La Niña events in 1979. We document the atmospheric circulation patterns associated with the strong correlation between ENSO and the rainfall over SB-NU after 1979 and hypothesize causes of the weaker correlation in the earlier period. In particular, numerical simulations produced using the UCLA atmospheric general circulation model showed important differences between upper tropospheric circulation patterns during ENSO cold episodes after the late 1970s relative to the earlier period. Such differences were consistent with changes in the impacts of La Niña events on SESA. The differences in Indian Ocean SST anomalies largely explained these results.


KEY WORDS: La Niña · Southeastern South America · 1970s change · SST anomalies · ENSO


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Cite this article as: Cazes-Boezio G, Talento S (2016) La Niña events before and after 1979 and their impact in southeastern South America during austral summer: role of the Indian Ocean. Clim Res 68:257-276. https://doi.org/10.3354/cr01354

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