The role of SST on the South American atmospheric circulation during January, February and March 2001 |
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Authors: | Anita Rodrigues de Moraes Drumond Tércio Ambrizzi |
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Institution: | 1. Department of Atmospheric Sciences, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of S?o Paulo, Rua do Mat?o, 1226, 05508-900, S?o Paulo, Brazil
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Abstract: | Precipitation deficits were observed over southeastern, northeastern and Central Brazil during the 2001 Austral Summer. They
contributed to the worsening of the energy crisis that was occurring in the country. A low-level anomalous anticyclonic circulation
observed over eastern Brazil enhanced the deviation of moisture transport that usually occurs from the Amazon Basin to southeastern
Brazil and inhibited the occurrence of South Atlantic Convergence Zone events in that period. However, an anomalous low-level
northerly moisture flux was observed over the La Plata Basin, and positive precipitation anomalies occurred over Bolivia,
Paraguay, northeastern Argentina and southern Brazil. Using the ensemble technique, a numerical study was carried out to investigate
the role of different sea surface temperature (SST) forcings observed over this anomalous South American atmospheric circulation.
Reynolds SST monthly means were used as boundary conditions to study the influence of South Atlantic, South Indian, South
Pacific and Equatorial Pacific oceans. The simulations were run from September 2000 to April 2001 using the Community Climate
Model version 3.6 General Circulation Model. Ten integrations using different initial conditions were done to each experiment.
Numerical experiments suggested that the combined influence of South Pacific and Equatorial Pacific oceans could be responsible
for the drought observed over Central Brazil. These experiments simulated the low-level anticyclonic anomaly observed over
eastern Brazil. However, both experiments have poorly reproduced the intensity of the anomalous low-level northerly moisture
flux observed over the La Plata Basin. Therefore, the intensity of the simulated precipitation anomalies over the subtropical
regions was much weaker than observed. |
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