Climate Dynamics

, Volume 37, Issue 9–10, pp 1771–1782 | Cite as

Processes governing the predictability of the Atlantic meridional overturning circulation in a coupled GCM

  • Pablo Ortega
  • Ed Hawkins
  • Rowan Sutton


The processes that govern the predictability of decadal variations in the North Atlantic meridional overturning circulation (MOC) are investigated in a long control simulation of the ECHO-G coupled atmosphere–ocean model. We elucidate the roles of local stochastic forcing by the atmosphere, and other potential ocean processes, and use our results to build a predictive regression model. The primary influence on MOC variability is found to come from air–sea heat fluxes over the Eastern Labrador Sea. The maximum correlation between such anomalies and the variations in the MOC occurs at a lead time of 2 years, but we demonstrate that the MOC integrates the heat flux variations over a period of 10 years. The corresponding univariate regression model accounts for 74.5% of the interannual variability in the MOC (after the Ekman component has been removed). Dense anomalies to the south of the Greenland-Scotland ridge are also shown to precede the overturning variations by 4–6 years, and provide a second predictor. With the inclusion of this second predictor the resulting regression model explains 82.8% of the total variance of the MOC. This final bivariate model is also tested during large rapid decadal overturning events. The sign of the rapid change is always well represented by the bivariate model, but the magnitude is usually underestimated, suggesting that other processes are also important for these large rapid decadal changes in the MOC.


Decadal predictability Atmosphere ocean general circulation model Meridional overturning circulation 



PO is funded by the projects SPECT and SPECT-MORE of the Spanish Ministry for Science and Innovation. EH is funded by the EU THOR programme and by NCAS-Climate. RS is supported by NCAS-Climate. PO thanks NCAS-Climate for hosting his visits to Reading when this analysis was done. We thank the three anonymous reviewers whose constructive comments helped improve the manuscript. The authors are also grateful to Fidel González-Rouco and Marisa Montoya for their valuable comments on a previous version of this paper.

Supplementary material

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  1. 1.Dpto. Astrofísica y Ciencias de la Atmósfera, Facultad de Ciencias FísicasUniversidad Complutense de MadridMadridSpain
  2. 2.NCAS-Climate, Department of MeteorologyUniversity of ReadingReadingUK

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