Multi-decadal thermohaline variability in an ocean–atmosphere general circulation model

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Article  

  Climate Dynamics
Publisher: Springer-Verlag Heidelberg
ISSN: 0930-7575 (Paper) 1432-0894 (Online)
DOI: 10.1007/s00382-004-0400-6
Issue: Volume 22, Numbers 6-7

Date:  June 2004
Page: 573  
Multi-decadal thermohaline variability in an ocean–atmosphere general circulation model
W. Cheng1 , R. Bleck2 and C. Rooth3

(1)  School of Oceanography, University of Washington, Campus Box 355351, Seattle, WA 98195, USA
(2)  Los Alamos National Laboratory, Mail Stop B296, Los Alamos, NM 87545, USA
(3)  Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker CSWY, Miami, FL 33149, USA

Received: 6 June 2003  Accepted: 5 January 2004  Published online: 26 March 2004

Abstract    A century scale integration of a near-global atmosphere–ocean model is used to study the multi-decadal variability of the thermohaline circulation (THC) in the Atlantic. The differences between the coupled and two supplementary ocean-only experiments suggest that a significant component of this variability is controlled by either a collective behavior of the ocean and the atmosphere, particularly in the form of air-sea heat exchange, or sub-monthly random noise present in the coupled system. Possible physical mechanisms giving rise to the mode of this THC variability are discussed. The SST anomaly associated with the THC variability resembles an interdecadal SST pattern extracted from observational data, as well as a pattern associated with the 50–60 year THC variability in the GFDL coupled model. In each case, a warming throughout the subpolar North Atlantic but concentrated along the Gulf Stream and its extension is indicated when the THC is strong. Concomitantly, surface air temperature has positive anomalies over the warmer ocean, with the strongest signal located downwind of the warmest SST anomalies and intruding into the western Eurasian Continent. In addition to the thermal response, there are also changes in the atmospheric flow pattern. More specifically, an anomalous northerly wind develops over the Labrador Sea when the THC is stronger than normal, suggesting a local primacy of the atmospheric forcing in the thermohaline perturbation structure.