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Stochastically-forced multidecadal variability in the North Atlantic: a model study

Stochastically-forced multidecadal variability in the North Atlantic: a model study
Stochastically-forced multidecadal variability in the North Atlantic: a model study
Observations show a multidecadal signal in the North Atlantic ocean, but the underlying mechanism and cause of its timescale remain unknown. Previous studies have suggested that it may be driven by the North Atlantic Oscillation (NAO), which is the dominant pattern of winter atmospheric variability. To further address this issue, the global ocean general circulation model, Nucleus for European Modelling of the Ocean (NEMO), is driven using a 2,000 years long white noise forcing associated with the NAO. Focusing on key ocean circulation patterns, we show that the Atlantic Meridional Overturning Circulation (AMOC) and Sub-polar gyre (SPG) strength both have enhanced power at low frequencies but no dominant timescale, and thus provide no evidence for a oscillatory ocean-only mode of variability. Instead, both indices respond linearly to the NAO forcing, but with different response times. The variability of the AMOC at 30°N is strongly enhanced on timescales longer than 90 years, while that of the SPG strength starts increasing at 15 years. The different response characteristics are confirmed by constructing simple statistical models that show AMOC and SPG variability can be related to the NAO variability of the previous 53 and 10 winters, respectively. Alternatively, the AMOC and the SPG strength can be reconstructed with Auto-regressive (AR) models of order seven and five, respectively. Both statistical models reconstruct interannual and multidecadal AMOC variability well, while on the other hand, the AR(5) reconstruction of the SPG strength only captures multidecadal variability. Using these methods to reconstruct ocean variables can be useful for prediction and model intercomparision.
North Atlantic, NAO, Atlantic Multidecadal Variability, Sub-polar gyre, Stochastic, OGCM
0930-7575
271-288
Mecking, J.V.
9b090069-5061-4340-b736-9690894ce203
Keenlyside, N.S.
22ae635e-b1bd-4040-9b0e-1fb315efce40
Greatbatch, R.J.
796e3a1c-20da-474b-bdef-a339f58dd7a1
Mecking, J.V.
9b090069-5061-4340-b736-9690894ce203
Keenlyside, N.S.
22ae635e-b1bd-4040-9b0e-1fb315efce40
Greatbatch, R.J.
796e3a1c-20da-474b-bdef-a339f58dd7a1

Mecking, J.V., Keenlyside, N.S. and Greatbatch, R.J. (2014) Stochastically-forced multidecadal variability in the North Atlantic: a model study. Climate Dynamics, 43 (1-2), 271-288. (doi:10.1007/s00382-013-1930-6).

Record type: Article

Abstract

Observations show a multidecadal signal in the North Atlantic ocean, but the underlying mechanism and cause of its timescale remain unknown. Previous studies have suggested that it may be driven by the North Atlantic Oscillation (NAO), which is the dominant pattern of winter atmospheric variability. To further address this issue, the global ocean general circulation model, Nucleus for European Modelling of the Ocean (NEMO), is driven using a 2,000 years long white noise forcing associated with the NAO. Focusing on key ocean circulation patterns, we show that the Atlantic Meridional Overturning Circulation (AMOC) and Sub-polar gyre (SPG) strength both have enhanced power at low frequencies but no dominant timescale, and thus provide no evidence for a oscillatory ocean-only mode of variability. Instead, both indices respond linearly to the NAO forcing, but with different response times. The variability of the AMOC at 30°N is strongly enhanced on timescales longer than 90 years, while that of the SPG strength starts increasing at 15 years. The different response characteristics are confirmed by constructing simple statistical models that show AMOC and SPG variability can be related to the NAO variability of the previous 53 and 10 winters, respectively. Alternatively, the AMOC and the SPG strength can be reconstructed with Auto-regressive (AR) models of order seven and five, respectively. Both statistical models reconstruct interannual and multidecadal AMOC variability well, while on the other hand, the AR(5) reconstruction of the SPG strength only captures multidecadal variability. Using these methods to reconstruct ocean variables can be useful for prediction and model intercomparision.

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More information

Published date: July 2014
Keywords: North Atlantic, NAO, Atlantic Multidecadal Variability, Sub-polar gyre, Stochastic, OGCM
Organisations: Physical Oceanography

Identifiers

Local EPrints ID: 378191
URI: http://eprints.soton.ac.uk/id/eprint/378191
ISSN: 0930-7575
PURE UUID: cd0be7b2-c31f-4b9a-819e-f1562d93dbd1

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Date deposited: 19 Jun 2015 12:38
Last modified: 14 Mar 2024 20:19

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Contributors

Author: J.V. Mecking
Author: N.S. Keenlyside
Author: R.J. Greatbatch

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