Response of North-Atlantic Ocean circulation to atmospheric weather regimes

Type Article
Date 2014-01
Language English
Author(s) Barrier Nicolas1, Cassou Christophe2, Deshayes Julie1, Treguier Anne-Marie1
Affiliation(s) 1 : CNRS,Ifremer UBO IRD, LPO, UMR 6523, Brest, France.
2 : CNRS, Cerfacs, Toulouse, France.
Source Journal Of Physical Oceanography (0022-3670) (Amer Meteorological Soc), 2014-01 , Vol. 44 , N. 1 , P. 179-201
DOI 10.1175/JPO-D-12-0217.1
WOS© Times Cited 37
Keyword(s) Circulation, Dynamics, Meridional overturning circulation, Atm, Ocean Structure, Phenomena, Gyres, North Atlantic Oscillation, Wind, Physical Meteorology and Climatology, Climate classification, regimes, Models and modeling, Ocean models
Abstract A new framework is proposed for investigating the atmospheric forcing of North-Atlantic ocean circulation. Instead of using classical modes of variability, such as the North-Atlantic Oscillation (NAO) or the East-Atlantic Pattern, we here use the weather regimes paradigm. Using this framework we avoid problems associated with the assumptions of orthogonality and symmetry that are particular to modal analysis and known to be unsuitable for the NAO.

Using ocean-only historical and sensitivity experiments, we investigate the impacts of the four winter weather regimes on horizontal and overturning circulations. Our results suggest that the Atlantic Ridge (AR), NAO− and NAO+ regimes induce a fast (monthly to interannual timescales) adjustment of the gyres via topographic Sverdrup dynamics and of the meridional overturning circulation via anomalous Ekman transport. The wind anomalies associated with the Scandinavian Blocking regime (SBL) are ineffective in driving a fast wind-driven oceanic adjustment.

We also estimate the response of both gyre and overturning circulations to persistent regime conditions. AR causes a strong, wind-driven reduction in the strengths of the subtropical and subpolar gyres, while NAO+ causes a strengthening of the subtropical gyre via wind-stress curl anomalies and of the subpolar gyre via heat flux anomalies. NAO− induces a southward shift of the gyres due to the southward displacement of the wind-stress curl. The SBL regime is found to impact the subpolar gyre only via anomalous heat fluxes. The overturning circulation is shown to spin-up following persistent SBL and NAO+ and to spin-down following persistent AR and NAO− conditions. These responses are driven by changes in deep water formation in the Labrador Sea
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