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Simulating the influence of the South Atlantic dipole on the South Atlantic convergence zone during neutral ENSO

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Abstract

The South Atlantic Convergence Zone (SACZ) is an intrinsic characteristic of the South American Summer Monsoon. In a recent study, we verified that the main mode of coupled variability over the South Atlantic (South Atlantic Dipole (SAD)) plays a role in modulating the position of extratropical cyclones that affect the SACZ precipitation. In this study, we perform numerical experiments to further investigate the mechanisms between SAD and the SACZ. Numerical experiments forced with prescribed SST anomalies showed that, even though the Atlantic SST affects the position of the cyclone associated with the SACZ, the atmospheric response and precipitation patterns over land are opposed to the observations. On the other hand, experiments forced with prescribed anomalous driving fields showed that the atmospheric component of SAD plays a significant role for the right position and intensity of precipitation associated with the SACZ. SAD negative anomalies provide the low-level and upper-level atmospheric support for the intensification of the cyclone at surface and for the increase in precipitation over the land portion of the SACZ. Therefore, the numerical experiments suggest that, during El Niño Southern Oscillation neutral conditions, the SACZ precipitation variability associated with SAD is largely dependent on the atmospheric variability rather than the underlying SST.

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Acknowledgment

We thank the anonymous reviewers for their valuable comments and suggestions for the improvement of this manuscript. We thank the support of NOAA Climate Program Office (NA07OAR4310211 and NA10OAR4310170). This research was conducted under the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS), sub-contract with the International Potato Center (SB120184). L. Carvalho thanks FAPESP (2008/58101-9) and CNPq [555768/2010-4]. We thank NASA for making available the MERRA reanalysis, NOAA for making available the SST data, and ANA for making available the precipitation station data. We also thank Dr. Brant Liebmann and Dr. David Allured for providing the precipitation station data. R. Bombardi thanks Dr. Saulo Freitas and Dr. Edmilson Dias de Freitas for their help with the BRAMS model.

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Correspondence to Rodrigo J. Bombardi.

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Bombardi, R.J., Carvalho, L.M.V. & Jones, C. Simulating the influence of the South Atlantic dipole on the South Atlantic convergence zone during neutral ENSO. Theor Appl Climatol 118, 251–269 (2014). https://doi.org/10.1007/s00704-013-1056-0

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  • DOI: https://doi.org/10.1007/s00704-013-1056-0

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