Intrinsic Variability of the Atlantic Meridional Overturning Circulation at Interannual-to-Multidecadal Time Scales

• Published in: Journal of Physical Oceanography
• Main Authors: Grégorio, Sandy, Penduff, Thierry, Sérazin, Guillaume, Molines, Jean-Marc, Barnier, Bernard, Hirschi, Joel
• Other Authors: Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), P.P. Shirshov Institute of Oceanology (SIO), Russian Academy of Sciences Moscow (RAS), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes 2016-2019 (UGA 2016-2019 ), National Oceanography Centre Southampton (NOC), University of Southampton
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; North Atlantic; Sea ice
• Online Access: https://hal.science/hal-03003568; https://hal.science/hal-03003568/document; https://hal.science/hal-03003568/file/%5B15200485%20-%20Journal%20of%20Physical%20Oceanography%5D%20Intrinsic%20Variability%20of%20the%20Atlantic%20Meridional%20Overturning%20Circulation%20at%20Interannual-to-Multidecadal%20Time%20Scales-1.pdf; https://doi.org/10.1175/JPO-D-14-0163.1

International audience The low-frequency variability of the Atlantic meridional overturning circulation (AMOC) is investigated from 2, 1 /48, and 1 /128 global ocean-sea ice simulations, with a specific focus on its internally generated (i.e., ''intrinsic'') component. A 327-yr climatological 1 /48 simulation, driven by a repeated seasonal cycle (i.e., a forcing devoid of interannual time scales), is shown to spontaneously generate a significant fraction R of the interannual-to-decadal AMOC variance obtained in a 50-yr ''fully forced'' hindcast (with reanalyzed atmospheric forcing including interannual time scales). This intrinsic variance fraction R slightly depends on whether AMOCs are computed in geopotential or density coordinates, and on the period considered in the climatological simulation, but the following features are quite robust when mesoscale eddies are simulated (at both 1 /48 and 1 /128 resolutions); R barely exceeds 5%-10% in the subpolar gyre but reaches 30%-50% at 348S, up to 20%-40% near 258N, and 40%-60% near the Gulf Stream. About 25% of the meridional heat transport interannual variability is attributed to intrinsic processes at 348S and near the Gulf Stream. Fourier and wavelet spectra, built from the 327-yr 1 /48 climatological simulation, further indicate that spectral peaks of intrinsic AMOC variability (i) are found at specific frequencies ranging from interannual to multidecadal, (ii) often extend over the whole meridional scale of gyres, (iii) stochastically change throughout these 327 yr, and (iv) sometimes match the spectral peaks found in the fully forced hindcast in the North Atlantic. Intrinsic AMOC variability is also detected at multidecadal time scales, with a marked meridional coherence between 358S and 258N (15-30 yr periods) and throughout the whole basin (50-90-yr periods).