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Intrinsic variability of the Atlantic Meridional Overturning Circulation at interannual-to-multidecadal time scales

Intrinsic variability of the Atlantic Meridional Overturning Circulation at interannual-to-multidecadal time scales
Intrinsic variability of the Atlantic Meridional Overturning Circulation at interannual-to-multidecadal time scales
The low-frequency variability of the Atlantic meridional overturning circulation (AMOC) is investigated from 2, ¼°, and ° global ocean–sea ice simulations, with a specific focus on its internally generated (i.e., “intrinsic”) component. A 327-yr climatological ¼° simulation, driven by a repeated seasonal cycle (i.e., a forcing devoid of interannual time scales), is shown to spontaneously generate a significant fraction R of the interannual-to-decadal AMOC variance obtained in a 50-yr “fully forced” hindcast (with reanalyzed atmospheric forcing including interannual time scales). This intrinsic variance fraction R slightly depends on whether AMOCs are computed in geopotential or density coordinates, and on the period considered in the climatological simulation, but the following features are quite robust when mesoscale eddies are simulated (at both ¼° and ° resolutions); R barely exceeds 5%–10% in the subpolar gyre but reaches 30%–50% at 34°S, up to 20%–40% near 25°N, and 40%–60% near the Gulf Stream. About 25% of the meridional heat transport interannual variability is attributed to intrinsic processes at 34°S and near the Gulf Stream. Fourier and wavelet spectra, built from the 327-yr ¼° climatological simulation, further indicate that spectral peaks of intrinsic AMOC variability (i) are found at specific frequencies ranging from interannual to multidecadal, (ii) often extend over the whole meridional scale of gyres, (iii) stochastically change throughout these 327 yr, and (iv) sometimes match the spectral peaks found in the fully forced hindcast in the North Atlantic. Intrinsic AMOC variability is also detected at multidecadal time scales, with a marked meridional coherence between 35°S and 25°N (15–30 yr periods) and throughout the whole basin (50–90-yr periods).
0022-3670
1929-1946
Grégorio, Sandy
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Penduff, Thierry
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Sérazin, Guillaume
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Molines, Jean-Marc
ff0e29c2-d4e8-4c72-995c-6e53801d823f
Barnier, Bernard
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Hirschi, Joël
c8a45006-a6e3-4319-b5f5-648e8ef98906
Grégorio, Sandy
fd8b1ae1-a845-46d2-bd43-e5639738e4b3
Penduff, Thierry
8b85eadc-4bb4-436a-a58a-9b2e279363bc
Sérazin, Guillaume
204a571e-3b8b-4d90-9a60-d4d0ff3d32e0
Molines, Jean-Marc
ff0e29c2-d4e8-4c72-995c-6e53801d823f
Barnier, Bernard
af67a33e-f7c3-4681-b37b-1fbebf74983a
Hirschi, Joël
c8a45006-a6e3-4319-b5f5-648e8ef98906

Grégorio, Sandy, Penduff, Thierry, Sérazin, Guillaume, Molines, Jean-Marc, Barnier, Bernard and Hirschi, Joël (2015) Intrinsic variability of the Atlantic Meridional Overturning Circulation at interannual-to-multidecadal time scales. Journal of Physical Oceanography, 45 (7), 1929-1946. (doi:10.1175/JPO-D-14-0163.1).

Record type: Article

Abstract

The low-frequency variability of the Atlantic meridional overturning circulation (AMOC) is investigated from 2, ¼°, and ° global ocean–sea ice simulations, with a specific focus on its internally generated (i.e., “intrinsic”) component. A 327-yr climatological ¼° simulation, driven by a repeated seasonal cycle (i.e., a forcing devoid of interannual time scales), is shown to spontaneously generate a significant fraction R of the interannual-to-decadal AMOC variance obtained in a 50-yr “fully forced” hindcast (with reanalyzed atmospheric forcing including interannual time scales). This intrinsic variance fraction R slightly depends on whether AMOCs are computed in geopotential or density coordinates, and on the period considered in the climatological simulation, but the following features are quite robust when mesoscale eddies are simulated (at both ¼° and ° resolutions); R barely exceeds 5%–10% in the subpolar gyre but reaches 30%–50% at 34°S, up to 20%–40% near 25°N, and 40%–60% near the Gulf Stream. About 25% of the meridional heat transport interannual variability is attributed to intrinsic processes at 34°S and near the Gulf Stream. Fourier and wavelet spectra, built from the 327-yr ¼° climatological simulation, further indicate that spectral peaks of intrinsic AMOC variability (i) are found at specific frequencies ranging from interannual to multidecadal, (ii) often extend over the whole meridional scale of gyres, (iii) stochastically change throughout these 327 yr, and (iv) sometimes match the spectral peaks found in the fully forced hindcast in the North Atlantic. Intrinsic AMOC variability is also detected at multidecadal time scales, with a marked meridional coherence between 35°S and 25°N (15–30 yr periods) and throughout the whole basin (50–90-yr periods).

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Published date: July 2015
Organisations: Marine Systems Modelling

Identifiers

Local EPrints ID: 380277
URI: http://eprints.soton.ac.uk/id/eprint/380277
ISSN: 0022-3670
PURE UUID: 9f3b63dd-333f-4ca9-bacd-752b78c20ffd

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Date deposited: 11 Aug 2015 13:16
Last modified: 14 Mar 2024 20:57

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Contributors

Author: Sandy Grégorio
Author: Thierry Penduff
Author: Guillaume Sérazin
Author: Jean-Marc Molines
Author: Bernard Barnier
Author: Joël Hirschi

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