Geostrophic Closure of the Zonally Averaged Atlantic Meridional Overturning Circulation

• Published in: Journal of Physical Oceanography
• Main Authors: Sevellec, F., Huck, Thierry
• Other Authors: Ocean and Earth Science Southampton, University of Southampton-National Oceanography Centre (NOC), 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)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: Atm/Ocean Structure/ Phenomena; Ocean circulation; Meridional overturning circulation; Baroclinic flows; Circulation/ Dynamics; Atlantic Ocean; Geographic location/entity; Ekman pumping; Thermohaline circulation; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Pacific; North Atlantic
• Online Access: https://hal.archives-ouvertes.fr/hal-01575298; https://doi.org/10.1175/JPO-D-14-0148.1

International audience It is typically assumed that the meridional density gradient in the North Atlantic is well and positively correlated with the Atlantic meridional overturning circulation (AMOC). In numerical “water-hosing” experiments, for example, imposing an anomalous freshwater flux in the Northern Hemisphere leads to a slowdown of the AMOC. However, on planetary scale, the first-order dynamics are linked to the geostrophic balance, relating the north–south pressure gradient to the zonal circulation. In this study, these two approaches are reconciled. At steady state and under geostrophic dynamics, an analytical expression is derived to relate the zonal and meridional pressure gradient. This solution is only valid where the meridional density gradient length scale is shorter than Earth’s curvature length scale, that is, north of 35°N. This theoretical expression links the north–south density gradient to the AMOC and can be used as a closure for zonally averaged ocean models. Assumptions and shortcomings of the approach are presented. Implications of these results for paleoclimate problems such as AMOC collapse and asymmetry in the meridional overturning circulation of the Atlantic and of the Pacific are discussed.