Locally and Remotely Forced Subtropical AMOC Variability: A Matter of Time Scales

Mechanisms driving the North Atlantic meridional overturning circulation (AMOC) variability at low frequency are of central interest for accurate climate predictions. Although the subpolar gyre region has been identified as a preferred place for generating climate time-scale signals, their southward...

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Bibliographic Details
Published in:Journal of Climate
Main Authors: Jamet, Quentin, Dewar, William K., Wienders, Nicolas, Deremble, Bruno, Close, Sally, Penduff, Thierry
Format: Article in Journal/Newspaper
Language:English
Published: Amer Meteorological Soc 2020
Subjects:
North Atlantic Ocean
Meridional overturning circulation
Ensembles
Ocean models
Climate variability
North Atlantic
Online Access:https://archimer.ifremer.fr/doc/00695/80736/84545.pdf
https://doi.org/10.1175/JCLI-D-19-0844.1
https://archimer.ifremer.fr/doc/00695/80736/
Description
Summary:Mechanisms driving the North Atlantic meridional overturning circulation (AMOC) variability at low frequency are of central interest for accurate climate predictions. Although the subpolar gyre region has been identified as a preferred place for generating climate time-scale signals, their southward propagation remains under consideration, complicating the interpretation of the observed time series provided by the Rapid Climate Change-Meridional Overturning Circulation and Heatflux Array-Western Boundary Time Series (RAPID-MOCHA-WBTS) program. In this study, we aim at disentangling the respective contribution of the local atmospheric forcing from signals of remote origin for the subtropical low-frequency AMOC variability. We analyze for this a set of four ensembles of a regional (20 degrees S-55 degrees N), eddy-resolving (1/12 degrees) North Atlantic oceanic configuration, where surface forcing and open boundary conditions are alternatively permuted from fully varying (realistic) to yearly repeating signals. Their analysis reveals the predominance of local, atmospherically forced signal at interannual time scales (2-10 years), whereas signals imposed by the boundaries are responsible for the decadal (10-30 years) part of the spectrum. Due to this marked time-scale separation, we show that, although the intergyre region exhibits peculiarities, most of the subtropical AMOC variability can be understood as a linear superposition of these two signals. Finally, we find that the decadal-scale, boundary-forced AMOC variability has both northern and southern origins, although the former dominates over the latter, including at the site of the RAPID array (26.5 degrees N).

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