Comparison of the Atlantic meridional overturning circulation between 1960 and 2007 in six ocean reanalysis products
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The mean and variability of the Atlantic meridional overturning circulation (AMOC), as represented in six ocean reanalysis products, are analyzed over the period 1960–2007. Particular focus is on multi-decadal trends and interannual variability at 26.5°N and 45°N. For four of the six reanalysis products, corresponding reference simulations obtained from the same models and forcing datasets but without the imposition of subsurface data constraints are included for comparison. An emphasis is placed on identifying general characteristics of the reanalysis representation of AMOC relative to their reference simulations without subsurface data constraints. The AMOC as simulated in these two sets are presented in the context of results from the Coordinated Ocean-ice Reference Experiments phase II (CORE-II) effort, wherein a common interannually varying atmospheric forcing data set was used to force a large and diverse set of global ocean-ice models. Relative to the reference simulations and CORE-II forced model simulations it is shown that (1) the reanalysis products tend to have greater AMOC mean strength and enhanced variance and (2) the reanalysis products are less consistent in their year-to-year AMOC changes. We also find that relative to the reference simulations (but not the CORE-II forced model simulations) the reanalysis products tend to have enhanced multi-decadal trends (from 1975–1995 to 1995–2007) in the mid to high latitudes of the northern hemisphere.
KeywordsAtlantic meridional overturning circulation (AMOC) Ocean data assimilation Ocean synthesis Ocean reanalysis Ocean reconstruction Decadal prediction
We wish to thank Keith Haines and Maria Valdivieso for early discussions and contributions. D.S. acknowledges the hospitality during a stimulating and pleasant research visit to the Climate and Global Dynamics division at NCAR. This work contributes to the Excellence Initiative “CliSAP” of the Universität Hamburg, funded through the German Science Foundation (DFG). D.M.S. was supported by the joint DECC/Defra Met Office Hadley Centre Climate Programme (GA01101) and the EU FP7 SPECS project. A.R.K. was funded through the NOAA Climate Program Office under the Climate Variability and Predictability Program grants NA09OAR4310163 and NA13OAR4310138, and by the NSF Collaborative Research EaSM2 Grant OCE-1243015. NCAR is sponsored by the National Science Foundation.
All relevant funding sources have been disclosed in the Acknowledgments. All authors of this paper provided consent to submit this work to Climate Dynamics.
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Conflict of interest
There are no potential conflicts of interest that would jeopardize the objectivity of this research.
This research did not involve any human participants or animals.
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