Multiple equilibria as a possible mechanism for decadal variability in the North Atlantic Ocean

• Published in: Journal of Climate
• Main Authors: Born, Andreas, Mignot, Juliette, Stocker, Thomas F.
• Other Authors: Climate and Environmental Physics Bern (CEP), Physikalisches Institut Bern, Universität Bern / University of Bern (UNIBE)-Universität Bern / University of Bern (UNIBE), Oeschger Centre for Climate Change Research (OCCR), Universität Bern / University of Bern (UNIBE), Processus de la variabilité climatique tropicale et impacts (PARVATI), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), European Project: 308378,EC:FP7:ENV,FP7-ENV-2012-two-stage,SPECS(2012), European Project: 8402271(1984)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph]; [SDU]Sciences of the Universe [physics]; North Atlantic
• Online Access: https://hal.science/hal-01496548; https://hal.science/hal-01496548/document; https://hal.science/hal-01496548/file/%5B15200442%20-%20Journal%20of%20Climate%5D%20Multiple%20Equilibria%20as%20a%20Possible%20Mechanism%20for%20Decadal%20Variability%20in%20the%20North%20Atlantic%20Ocean.pdf; https://doi.org/10.1175/JCLI-D-14-00813.1

International audience Decadal climate variability in the North Atlantic has received increased attention in recent years, because modeling results suggest predictability of heat content and circulation indices several years ahead. However, determining the applicability of these results in the real world is challenging because of an incomplete understanding of the underlying mechanisms. Here, the authors show that recent attempts to reconstruct the decadal variations in one of the dominant circulation systems of the region, the subpolar gyre (SPG), are not always consistent. A coherent picture is partly recovered by a simple conceptual model solely forced by reanalyzed surface air temperatures. This confirms that surface heat flux indeed plays a leading role for this type of variability, as has been suggested in previous studies. The results further suggest that large variations in the SPG correspond to the crossing of a bifurcation point that is predicted from idealized experiments and an analytical solution of the model used herein. Performance of this conceptual model is tested against a statistical stochastic model. Hysteresis and the existence of two stable modes of the SPG circulation shape its response to forcing by atmospheric temperatures. The identification of the essential dynamics and the reduction to a minimal model of SPG variability provide a quantifiable basis and a framework for future studies on decadal climate variability and predictability.