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

Sévellec, Florian; Hirschi, Joel J.-M.; Blaker, Adam T. ORCID: https://orcid.org/0000-0001-5454-0131. 2013 On the Near-Inertial Resonance of the Atlantic Meridional Overturning Circulation. Journal of Physical Oceanography, 43 (12). 2661-2672. 10.1175/JPO-D-13-092.1

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Official URL: http://dx.doi.org/10.1175/JPO-D-13-092.1

Abstract/Summary

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.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1175/JPO-D-13-092.1
ISSN:	0022-3670
Date made live:	13 Jan 2014 15:21 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/504488

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1175/JPO-D-13-092.1

ISSN:

0022-3670

Date made live:

13 Jan 2014 15:21 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/504488