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Mechanisms of Interannual Variations of the Meridional Overturning Circulation of the North Atlantic OceanThe authors investigate the nature of the interannual variability of the meridional overturning circulation (MOC) of the North Atlantic Ocean using an Estimating the Circulation and Climate of the Ocean (ECCO) assimilation product for the period of 1993-2003. The time series of the first empirical orthogonal function of the MOC is found to be correlated with the North Atlantic Oscillation (NAO) index, while the associated circulation anomalies correspond to cells extending over the full ocean depth. Model sensitivity experiments suggest that the wind is responsible for most of this interannual variability, at least south of 40(deg)N. A dynamical decomposition of the meridional streamfunction allows a further look into the mechanisms. In particular, the contributions associated with 1) the Ekman flow and its depth-independent compensation, 2) the vertical shear flow, and 3) the barotropic gyre flowing over zonally varying topography are examined. Ekman processes are found to dominate the shorter time scales (1.5-3 yr), while for longer time scales (3-10 yr) the MOC variations associated with vertical shear flow are of greater importance. The latter is primarily caused by heaving of the pycnocline in the western subtropics associated with the stronger wind forcing. Finally, how these changes in the MOC affect the meridional heat transport (MHT) is examined. It is found that overall, Ekman processes explain a larger part of interannual variability (3-10 yr) for MHT (57%) than for the MOC (33%).
Document ID
20080036107
Acquisition Source
Jet Propulsion Laboratory
Document Type
Reprint (Version printed in journal)
Authors
Cabanes, Cecile
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Lee, Tong
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Fu, Lee-Lueng
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Date Acquired
August 24, 2013
Publication Date
February 1, 2008
Publication Information
Publication: Journal of Physical Oceanography
Publisher: American Meteorological Society
Volume: 38
Issue: 2
Subject Category
Oceanography
Distribution Limits
Public
Copyright
Other
Keywords
meridional heat transport
meridional overturning circulation (MOC)
Estimating the Circulation and Climate of the Ocean (ECCO)

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