The University of Southampton
University of Southampton Institutional Repository

On the Near-Inertial Resonance of the Atlantic Meridional Overturning Circulation

On the Near-Inertial Resonance of the Atlantic Meridional Overturning Circulation
On the Near-Inertial Resonance of the Atlantic Meridional Overturning Circulation
The Atlantic meridional overturning circulation (AMOC) is a crucial component of the global climate system. It is responsible for around a quarter of the global northward heat transport and contributes to the mild European climate. Observations and numerical models suggest a wide range of AMOC variability. Recent results from an ocean general circulation model (OGCM) in a high-resolution configuration (¼°) suggest the existence of superinertial variability of the AMOC. In this study, the validity of this result in a theoretical framework is tested. At a low Rossby number and in the presence of Rayleigh friction, it is demonstrated that, unlike a typical forced damped oscillator (which shows subinertial resonance), the AMOC undergoes both super- and subinertial resonances (except at low latitudes and for high friction). A dimensionless number Sr, measuring the ratio of ageo- to geostrophic forcing (i.e., the zonal versus meridional pressure gradients), indicates which of these resonances dominates. If Sr ? 1, the AMOC variability is mainly driven by geostrophic forcing and shows subinertial resonance. Alternatively and consistent with the recently published ¼° OGCM experiments, if Sr ? 1, the AMOC variability is mainly driven by the ageostrophic forcing and shows superinertial resonance. In both regimes, a forcing of ±1 K induces an AMOC variability of ±10 Sv (1 Sv ? 106 m3 s?1) through these near-inertial resonance phenomena. It is also shown that, as expected from numerical simulations, the spatial structure of the near-inertial AMOC variability corresponds to equatorward-propagating waves equivalent to baroclinic Poincaré waves. The long-time average of this resonance phenomenon, raising and depressing the pycnocline, could contribute to the mixing of the ocean stratification.
0022-3670
2661-2672
Sévellec, Florian
01569d6c-65b0-4270-af2a-35b0a77c9140
Hirschi, Joël J.-M.
c8a45006-a6e3-4319-b5f5-648e8ef98906
Blaker, Adam T.
94efe8b2-c744-4e90-87d7-db19ffa41200
Sévellec, Florian
01569d6c-65b0-4270-af2a-35b0a77c9140
Hirschi, Joël J.-M.
c8a45006-a6e3-4319-b5f5-648e8ef98906
Blaker, Adam T.
94efe8b2-c744-4e90-87d7-db19ffa41200

Sévellec, Florian, Hirschi, Joël J.-M. and Blaker, Adam T. (2013) On the Near-Inertial Resonance of the Atlantic Meridional Overturning Circulation. Journal of Physical Oceanography, 43 (12), 2661-2672. (doi:10.1175/JPO-D-13-092.1).

Record type: Article

Abstract

The Atlantic meridional overturning circulation (AMOC) is a crucial component of the global climate system. It is responsible for around a quarter of the global northward heat transport and contributes to the mild European climate. Observations and numerical models suggest a wide range of AMOC variability. Recent results from an ocean general circulation model (OGCM) in a high-resolution configuration (¼°) suggest the existence of superinertial variability of the AMOC. In this study, the validity of this result in a theoretical framework is tested. At a low Rossby number and in the presence of Rayleigh friction, it is demonstrated that, unlike a typical forced damped oscillator (which shows subinertial resonance), the AMOC undergoes both super- and subinertial resonances (except at low latitudes and for high friction). A dimensionless number Sr, measuring the ratio of ageo- to geostrophic forcing (i.e., the zonal versus meridional pressure gradients), indicates which of these resonances dominates. If Sr ? 1, the AMOC variability is mainly driven by geostrophic forcing and shows subinertial resonance. Alternatively and consistent with the recently published ¼° OGCM experiments, if Sr ? 1, the AMOC variability is mainly driven by the ageostrophic forcing and shows superinertial resonance. In both regimes, a forcing of ±1 K induces an AMOC variability of ±10 Sv (1 Sv ? 106 m3 s?1) through these near-inertial resonance phenomena. It is also shown that, as expected from numerical simulations, the spatial structure of the near-inertial AMOC variability corresponds to equatorward-propagating waves equivalent to baroclinic Poincaré waves. The long-time average of this resonance phenomenon, raising and depressing the pycnocline, could contribute to the mixing of the ocean stratification.

Text
jpo-d-13-092%2E1.pdf - Other
Download (5MB)

More information

Published date: December 2013
Organisations: Marine Systems Modelling, Physical Oceanography

Identifiers

Local EPrints ID: 361114
URI: http://eprints.soton.ac.uk/id/eprint/361114
ISSN: 0022-3670
PURE UUID: eca8aab5-7fe6-426c-a460-67da64487da1

Catalogue record

Date deposited: 13 Jan 2014 15:12
Last modified: 14 Mar 2024 15:46

Export record

Altmetrics

Contributors

Author: Joël J.-M. Hirschi
Author: Adam T. Blaker

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×