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Multiple causes of interannual sea surface temperature variability in the equatorial Atlantic Ocean

Abstract

The eastern equatorial Atlantic Ocean is subject to interannual fluctuations of sea surface temperatures, with climatic impacts on the surrounding continents1,2,3. The dynamic mechanism underlying Atlantic temperature variability is thought to be similar to that of the El Niño/Southern Oscillation (ENSO) in the equatorial Pacific4,5, where air–sea coupling leads to a positive feedback between surface winds in the western basin, sea surface temperature in the eastern basin, and equatorial oceanic heat content. Here we use a suite of observational data, climate reanalysis products, and general circulation model simulations to reassess the factors driving the interannual variability. We show that some of the warm events can not be explained by previously identified equatorial wind stress forcing and ENSO-like dynamics. Instead, these events are driven by a mechanism in which surface wind forcing just north of the equator induces warm ocean temperature anomalies that are subsequently advected toward the equator. We find the surface wind patterns are associated with long-lived subtropical sea surface temperature anomalies and suggest they therefore reflect a link between equatorial and subtropical Atlantic variability.

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Figure 1: Correlation between equatorial boreal spring surface winds and cold tongue summer SST for four data sets.
Figure 2: Composite evolution of equatorial Atlantic warm events in the NCEP reanalysis.
Figure 3: Composite maps showing the evolution of non-canonical and canonical warm events in April and July.
Figure 4: Heat budget terms in the eastern equatorial Atlantic for the OFES hindcast, and running correlation of wind and SST anomalies in four data sets.

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Acknowledgements

The authors would like to thank S-P. Xie, A. Timmermann and F-F. Jin for their comments on this work. OFES integrations were carried out at the Earth Simulator Center, Yokohama, Japan. We acknowledge the modelling groups, the Program for Climate Model Diagnosis and Intercomparison (PCMDI) and the WCRP’s Working Group on Coupled Modelling (WGCM) for their roles in making available the WCRP CMIP3 multi-model data set. Support of this data set is provided by the Office of Science, US Department of Energy.

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I.R. conceived the central idea, carried out the analysis, and wrote the paper. H.S. performed the OFES hindcast integrations. All authors provided guidance for the analysis and commented on the manuscript.

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Correspondence to Ingo Richter.

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The authors declare no competing financial interests.

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Richter, I., Behera, S., Masumoto, Y. et al. Multiple causes of interannual sea surface temperature variability in the equatorial Atlantic Ocean. Nature Geosci 6, 43–47 (2013). https://doi.org/10.1038/ngeo1660

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