A decomposition of the Atlantic Meridional Overturning Circulation into physical components using its sensitivity to vertical diffusivity

• Published in: Journal of Physical Oceanography
• Main Authors: Mignot, Juliette, Levermann, Anders, Griesel, Alexa
• Other Authors: 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), Potsdam Institute for Climate Impact Research (PIK)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2006
• Subjects: [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; Southern Ocean; Greenland; Irminger Sea; Greenland-Scotland Ridge; Nordic Seas; North Atlantic; Sea ice
• Online Access: https://hal.science/hal-00164658; https://hal.science/hal-00164658/document; https://hal.science/hal-00164658/file/%5B15200485%20-%20Journal%20of%20Physical%20Oceanography%5D%20A%20Decomposition%20of%20the%20Atlantic%20Meridional%20Overturning%20Circulation%20into%20Physical%20Components%20Using%20Its%20Sensitivity%20to%20Vertical%20Diffusivity.pdf; https://doi.org/10.1175/JPO2891.1

International audience The sensitivity of the Atlantic Ocean meridional overturning circulation to the vertical diffusion coefficient in the global coupled atmosphere–ocean–sea ice model CLIMBER-3 is investigated. An important feature of the three-dimensional ocean model is its low-diffusive tracer advection scheme. The strength Mmax of the Atlantic overturning is decomposed into three components: 1) the flow MS exported southward at 30°S, 2) the large-scale upward flow that balances vertical diffusion in the Atlantic, and 3) a winddependent upwelling flux Wbound along the Atlantic boundaries that is not due to vertical diffusion. The export of water at 30°S varies only weakly with , but is strongly correlated with the strength of the overflow over the Greenland–Scotland ridge. The location of deep convection is found to be mixing dependent such that a shift from the Nordic seas to the Irminger Sea is detected for high values of . The ratio R MS/Mmax gives a measure of the interhemispheric overturning efficiency and is found to decrease linearly with . The diffusion-induced upwelling in the Atlantic is mostly due to the uniform background value of while parameterization of enhanced mixing over rough topography and in stratified areas gives only a weak contribution to the overturning strength. It increases linearly with . This is consistent with the classic 2/3 scaling law only when taking the linear variation of the density difference to into account. The value of Wbound is roughly constant with but depends linearly on the wind stress strength in the North Atlantic. The pycnocline depth is not sensitive to changes in in the model used herein, and the results suggest that it is primarily set by the forcing of the Southern Ocean winds. The scaling of the total overturning strength with depends on the combined sensitivity of each of the terms to . In the range of background diffusivity values in which no switch in deep convection sites is detected, Mmax scales linearly with the vertical diffusivity. It is argued ...