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Predictability and decadal variability of the North Atlantic ocean state evaluated from a realistic ocean

Predictability and decadal variability of the North Atlantic ocean state evaluated from a realistic ocean
Predictability and decadal variability of the North Atlantic ocean state evaluated from a realistic ocean
This study investigates the excitation of decadal variability and predictability of the ocean climate state in the North Atlantic. Specifically, initial linear optimal perturbations (LOPs) in temperature and salinity that vary with depth, longitude, and latitude are computed, and the maximum impact on the ocean of these perturbations is evaluated in a realistic ocean general circulation model. The computations of the LOPs involve a maximization procedure based on Lagrange multipliers in a nonautonomous context. To assess the impact of these perturbations four different measures of the North Atlantic Ocean state are used: meridional volume and heat transports (MVT and MHT) and spatially averaged sea surface temperature (SST) and ocean heat content (OHC). It is shown that these metrics are dramatically different with regard to predictability. Whereas OHC and SST can be efficiently modified only by basin-scale anomalies, MVT and MHT are also strongly affected by smaller-scale perturbations. This suggests that instantaneous or even annual-mean values of MVT and MHT are less predictable than SST and OHC. Only when averaged over several decades do the former two metrics have predictability comparable to the latter two, which highlights the need for long-term observations of the Atlantic meridional overturning circulation in order to accumulate climatically relevant data. This study also suggests that initial errors in ocean temperature of a few millikelvins, encompassing both the upper and deep ocean, can lead to ~0.1-K errors in the predictions of North Atlantic sea surface temperature on interannual time scales. This transient error growth peaks for SST and OHC after about 6 and 10 years, respectively, implying a potential predictability barrier.
Meridional overturning circulation, Ocean circulation, Ocean dynamics, Climate prediction, Climate variability, General circulation models
0894-8755
477-498
Sevellec, Florian
01569d6c-65b0-4270-af2a-35b0a77c9140
Fedorov, Alexey V.
c4234650-4a09-4d65-b6fc-cebd592a788f
Sevellec, Florian
01569d6c-65b0-4270-af2a-35b0a77c9140
Fedorov, Alexey V.
c4234650-4a09-4d65-b6fc-cebd592a788f

Sevellec, Florian and Fedorov, Alexey V. (2017) Predictability and decadal variability of the North Atlantic ocean state evaluated from a realistic ocean. Journal of Climate, 30 (2), 477-498. (doi:10.1175/JCLI-D-16-0323.1).

Record type: Article

Abstract

This study investigates the excitation of decadal variability and predictability of the ocean climate state in the North Atlantic. Specifically, initial linear optimal perturbations (LOPs) in temperature and salinity that vary with depth, longitude, and latitude are computed, and the maximum impact on the ocean of these perturbations is evaluated in a realistic ocean general circulation model. The computations of the LOPs involve a maximization procedure based on Lagrange multipliers in a nonautonomous context. To assess the impact of these perturbations four different measures of the North Atlantic Ocean state are used: meridional volume and heat transports (MVT and MHT) and spatially averaged sea surface temperature (SST) and ocean heat content (OHC). It is shown that these metrics are dramatically different with regard to predictability. Whereas OHC and SST can be efficiently modified only by basin-scale anomalies, MVT and MHT are also strongly affected by smaller-scale perturbations. This suggests that instantaneous or even annual-mean values of MVT and MHT are less predictable than SST and OHC. Only when averaged over several decades do the former two metrics have predictability comparable to the latter two, which highlights the need for long-term observations of the Atlantic meridional overturning circulation in order to accumulate climatically relevant data. This study also suggests that initial errors in ocean temperature of a few millikelvins, encompassing both the upper and deep ocean, can lead to ~0.1-K errors in the predictions of North Atlantic sea surface temperature on interannual time scales. This transient error growth peaks for SST and OHC after about 6 and 10 years, respectively, implying a potential predictability barrier.

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More information

Accepted/In Press date: 12 September 2016
e-pub ahead of print date: 22 December 2016
Published date: 1 January 2017
Keywords: Meridional overturning circulation, Ocean circulation, Ocean dynamics, Climate prediction, Climate variability, General circulation models
Organisations: Physical Oceanography

Identifiers

Local EPrints ID: 405778
URI: http://eprints.soton.ac.uk/id/eprint/405778
ISSN: 0894-8755
PURE UUID: 32a28a37-41d9-4428-a010-13d1a44549a3

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Date deposited: 10 Feb 2017 12:02
Last modified: 15 Mar 2024 06:20

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Author: Alexey V. Fedorov

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