Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
doi:10.5194/cp-2017-49
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
15 May 2017
Review status
This discussion paper is under review for the journal Climate of the Past (CP).
Atlantic Multidecadal Variability from the Last Millennium Reanalysis
Hansi K. A. Singh1, Gregory J. Hakim2, Robert Tardif2, Julien Emile-Geay3, and David C. Noone4 1Pacific Northwest National Laboratory, US Department of Energy, Richland WA, USA
2Department of Atmospheric Sciences, University of Washington, Seattle WA, USA
3Department of Earth Sciences, University of Southern California, Los Angeles CA, USA
4College of Earth, Ocean, and Atmospheric Sciences, Corvallis OR, USA
Abstract. The Last Millennial Reanalysis (LMR) employs a data assimilation approach to reconstruct climate fields from annually-resolved proxy data over years 0–2000CE. We use the LMR to examine Atlantic Multidecadal Variability (AMV) over the last two millennia, and find several robust thermodynamic features associated with a positive Atlantic Multidecadal Oscillation (AMO) index that reveal a dynamically-consistent pattern of variability: the Atlantic and most continents warm; sea ice thins over the Arctic and retreats over the Greenland-Iceland-Norwegian Seas; and equatorial precipitation shifts northward. The latter is consistent with anomalous southward energy transport mediated by the atmosphere. Net downward shortwave radiation increases at both the top-of-atmosphere and surface, indicating a decrease in planetary albedo, likely due to a decrease in low clouds. Heat is absorbed by the climate system and the oceans warm. Wavelet analysis of the AMV time series shows a reddening of the frequency spectrum at the 50-to-100-year time scale, but no evidence of a distinct multidecadal or centennial spectral peak. This latter result is insensitive to both choice of prior model and calibration dataset used in the data assimilation algorithm, suggesting that the lack of a distinct multidecadal spectral peak is a robust result.

Citation: Singh, H. K. A., Hakim, G. J., Tardif, R., Emile-Geay, J., and Noone, D. C.: Atlantic Multidecadal Variability from the Last Millennium Reanalysis, Clim. Past Discuss., doi:10.5194/cp-2017-49, in review, 2017.
Hansi K. A. Singh et al.
Hansi K. A. Singh et al.
Hansi K. A. Singh et al.

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Short summary
Atlantic Multidecadal Variability (AMV) is prominent in the climate system. We study AMV over the last 2000 years using a novel proxy reanalysis product, the Last Millennial Reanalysis. We find that AMV is linked to continental warming, Arctic sea ice retreat, and an Atlantic precipitation shift. Low clouds decrease globally. We also find that there is no distinct multidecadal spectral peak in AMV over the last two millennia, suggesting that anthropogenic activities may modify AMV.
Atlantic Multidecadal Variability (AMV) is prominent in the climate system. We study AMV over...
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