Study of the causes and eff ects of the Atlantic Meridional Overturning Circulationn

• Main Author: Marini, Camille
• Other Authors: Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), 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 Paris), 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), Université Pierre et Marie Curie - Paris VI, Claude Frankignoul
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2011
• Subjects: Atlantic Meridional Overturning Circulation; Atlantic Multidecadal Oscillation; El Nino Southern Oscillation; decadal and multidecadal variability; Arctic Oscillation; Southern Annular Mode; Linear Inverse Modeling; Volcanic eruptions; Circulation Méridienne de renversement Atlantique; Oscillation Multidécennale Atlantique; El Nino; Variabilité décennale; Variabilité multidécennale; Teleconnections; Oscillation Arctique; Mode Annulaire Sud; Modéle Linéaire Inverse; Eruptions volcaniques; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Arctic; Drake Passage; Pacific; Arctique*; North Atlantic
• Online Access: https://tel.archives-ouvertes.fr/tel-00994862; https://tel.archives-ouvertes.fr/tel-00994862/document; https://tel.archives-ouvertes.fr/tel-00994862/file/Thesis_Marini.pdf

In the first part of this thesis, we study the influence of the Southern Annular Mode (SAM) onto the Atlantic Meridional Overturning Circulation (AMOC) in a control simulation with the IPSLCM4 model. We show that a positive phase of the SAM, corresponding to an intensification of the Westerlies south of 45 ̊S, leads to an acceleration of the AMOC after 8 years, via an atmospheric teleconnection, which is likely to be model-dependent. We also find a link between the SAM and the AMOC at a multidecadal time scale. Positive salt anomalies, created by a positive SAM, enter the South Atlantic from the Drake Passage and, more importantly, via the Aghulas leakage; they propagate northward, eventually reaching the northern North Atlantic where they decrease the vertical stratification and thus increase the AMOC. In the second part of this thesis, we study to what extent the Atlantic Multidecadal Oscillation (AMO) reflects the AMOC fluctuations, and what are the other signals that influence it in natural climate variability conditions and with the external forcings of the 20th century. We use a dynamical filter, based on linear inverse modeling (LIM), to decompose the North Atlantic sea surface temperature (SST) field into a global trend, an El Nino Southern Oscillation-related part (ENSO), a part associated with Pacific decadal variability and a residual. In the historical simulation with the IPSLCM5 climate model, removing the global trend from the AMO with LIM yields to better correlations with the AMOC than removing a linear trend or the global mean SST. We also find that removing the ENSO-related part from the AMO with LIM leads to small changes, and even better correlations with the AMOC. Additionaly removing the signal associated to Pacific decadal variability leads to considerable changes in the AMO, which becomes much less correlated to the AMOC. The robustness of these results is demonstrated by performing the LIM decomposition in control simulations with five different climate models. Besides, the LIM filter is ...