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Gulf Stream Variability in Five Oceanic General Circulation Models

Gaëlle de Coëtlogon Centre d’Etude Terrestre et Planétaire, IUT de Vélizy, Vélizy, France

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Claude Frankignoul Laboratoire d’Océanographie Dynamique et de Climatologie, Université Pierre et Marie Curie, Paris, France

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Mats Bentsen Nansen Environmental and Remote Sensing Center, Bergen, Norway

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Claire Delon Laboratoire d’Aérologie, Observatoire Midi Pyrénées, Toulouse, France

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Helmuth Haak Max Planck Institute for Meteorology, Hamburg, Germany

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Simona Masina Istituto Nazionale di Geofisica et Vulcanologia, Bologna, Italy

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Anne Pardaens Hadley Centre for Climate Prediction and Research, Met Office, Exeter, United Kingdom

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Print Publication:
01 Nov 2006
DOI:
https://doi.org/10.1175/JPO2963.1
Page(s):
2119–2135
Restricted access

Abstract

Five non-eddy-resolving oceanic general circulation models driven by atmospheric fluxes derived from the NCEP reanalysis are used to investigate the link between the Gulf Stream (GS) variability, the atmospheric circulation, and the Atlantic meridional overturning circulation (AMOC). Despite the limited model resolution, the temperature at the 200-m depth along the mean GS axis behaves similarly in most models to that observed, and it is also well correlated with the North Atlantic Oscillation (NAO), indicating that a northward (southward) GS shift lags a positive (negative) NAO phase by 0–2 yr. The northward shift is accompanied by an increase in the GS transport, and conversely the southward shift with a decrease in the GS transport. Two dominant time scales appear in the response of the GS transport to the NAO forcing: a fast time scale (less than 1 month) for the barotropic component, and a slower one (about 2 yr) for the baroclinic component. In addition, the two components are weakly coupled. The GS response seems broadly consistent with a linear adjustment to the changes in the wind stress curl, and evidence for baroclinic Rossby wave propagation is found in the southern part of the subtropical gyre. However, the GS shifts are also affected by basin-scale changes in the oceanic conditions, and they are well correlated in most models with the changes in the AMOC. A larger AMOC is found when the GS is stronger and displaced northward, and a higher correlation is found when the observed changes of the GS position are used in the comparison. The relation between the GS and the AMOC could be explained by the inherent coupling between the thermohaline and the wind-driven circulation, or by the NAO variability driving them on similar time scales in the models.

Corresponding author address: Gaëlle de Coëtlogon, Centre d’Etude Terrestre et Planétaire, IUT de Vélizy, 10–12 avenue de l’Europe, 78140 Vélizy, France. Email: gdc@cetp.ipsl.fr

Abstract

Five non-eddy-resolving oceanic general circulation models driven by atmospheric fluxes derived from the NCEP reanalysis are used to investigate the link between the Gulf Stream (GS) variability, the atmospheric circulation, and the Atlantic meridional overturning circulation (AMOC). Despite the limited model resolution, the temperature at the 200-m depth along the mean GS axis behaves similarly in most models to that observed, and it is also well correlated with the North Atlantic Oscillation (NAO), indicating that a northward (southward) GS shift lags a positive (negative) NAO phase by 0–2 yr. The northward shift is accompanied by an increase in the GS transport, and conversely the southward shift with a decrease in the GS transport. Two dominant time scales appear in the response of the GS transport to the NAO forcing: a fast time scale (less than 1 month) for the barotropic component, and a slower one (about 2 yr) for the baroclinic component. In addition, the two components are weakly coupled. The GS response seems broadly consistent with a linear adjustment to the changes in the wind stress curl, and evidence for baroclinic Rossby wave propagation is found in the southern part of the subtropical gyre. However, the GS shifts are also affected by basin-scale changes in the oceanic conditions, and they are well correlated in most models with the changes in the AMOC. A larger AMOC is found when the GS is stronger and displaced northward, and a higher correlation is found when the observed changes of the GS position are used in the comparison. The relation between the GS and the AMOC could be explained by the inherent coupling between the thermohaline and the wind-driven circulation, or by the NAO variability driving them on similar time scales in the models.

Corresponding author address: Gaëlle de Coëtlogon, Centre d’Etude Terrestre et Planétaire, IUT de Vélizy, 10–12 avenue de l’Europe, 78140 Vélizy, France. Email: gdc@cetp.ipsl.fr

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