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

• Published in: Journal of Climate
• Main Authors: Jamet, Quentin, Dewar, William, Wienders, Nicolas, Deremble, Bruno, Close, Sally, Penduff, Thierry
• Other Authors: Laboratoire de physique des océans (LPO), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Florida State University Tallahassee (FSU), Department of Earth, Ocean and Atmospheric Science Tallahassee (FSU, Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Laboratoire d'Océanographie Physique et Spatiale (LOPS), Laboratoire des Écoulements Géophysiques et Industriels Grenoble (LEGI), Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; North Atlantic
• Online Access: https://hal.archives-ouvertes.fr/hal-02879821; https://hal.archives-ouvertes.fr/hal-02879821/document; https://hal.archives-ouvertes.fr/hal-02879821/file/Jamet2020.pdf; https://doi.org/10.1175/JCLI-D-19-0844.1

International audience 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 timescale 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 (208S-558N), eddy-resolving (1/128) 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 timescale 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 (26.58N).