Variability of the South Atlantic Convergence Zone Simulated by an Atmospheric General Circulation Model

Marcelo Barreiro Department of Oceanography, Texas A&M University, College Station, Texas

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Ping Chang Department of Oceanography, Texas A&M University, College Station, Texas

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R. Saravanan National Center for Atmospheric Research, Boulder, Colorado

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Abstract

Interannual and decadal variability of the South Atlantic convergence zone (SACZ) during austral summer [season January–February–March (JFM)] is investigated. An attempt is made to separate the forced variability from the internal variability. This is accomplished by applying a signal-to-noise optimization procedure to an ensemble of multidecadal integrations of the latest version of the NCAR Community Climate Model (CCM3) forced with observed SST. The result yields two dominant forced atmospheric responses: a local response to Atlantic SST anomalies with interannual-decadal timescales and a remote response to Pacific SST anomalies at interannual timescales. The former is localized within the South Atlantic Ocean with almost no signal over land, consisting of a dipolelike structure in precipitation close to the coast of South America accompanied by a clockwise anomalous circulation of surface winds. The latter manifests itself mainly in the upper-level circulation, consisting of a northeastward shift of the SACZ with associated rainfall anomalies during warm ENSO events.

Corresponding author address: Dr. R. Saravanan, NCAR, P.O.Box 3000, Boulder, CO 80307-3000. Email: svn@ncar.ucar.edu

Abstract

Interannual and decadal variability of the South Atlantic convergence zone (SACZ) during austral summer [season January–February–March (JFM)] is investigated. An attempt is made to separate the forced variability from the internal variability. This is accomplished by applying a signal-to-noise optimization procedure to an ensemble of multidecadal integrations of the latest version of the NCAR Community Climate Model (CCM3) forced with observed SST. The result yields two dominant forced atmospheric responses: a local response to Atlantic SST anomalies with interannual-decadal timescales and a remote response to Pacific SST anomalies at interannual timescales. The former is localized within the South Atlantic Ocean with almost no signal over land, consisting of a dipolelike structure in precipitation close to the coast of South America accompanied by a clockwise anomalous circulation of surface winds. The latter manifests itself mainly in the upper-level circulation, consisting of a northeastward shift of the SACZ with associated rainfall anomalies during warm ENSO events.

Corresponding author address: Dr. R. Saravanan, NCAR, P.O.Box 3000, Boulder, CO 80307-3000. Email: svn@ncar.ucar.edu

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