Simulated Variability of the Circulation in the North Atlantic from 1953 to 2003

Abstract

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Mechanisms for decadal scale variability in a simulated Atlantic meridional overturning circulation

“…So far the results are in agreement with the traditional view that NAO is responsible for the deep water formation, and hence AMOC (e.g., Dickson et al 1996;Curry et al 1998;Häkkinen 1999;Eden and Willebrand 2001;Bentsen et al 2004;Deshayes and Frankignoul 2008), where in this model there is a correlation of 0.4 between NAO and AMOC. However, there is one important difference in this study: For the Nordic Seas the convection does not determine the water mass exchange across the GRS but is rather a result of it.…”

“…Previously suggested candidates for AMOC variability are oceanic response to aggregated atmospheric white noise forcing at high northern latitudes where dense water is produced (e.g., Dickson et al 1996;Häkkinen 1999;Delworth and Greatbatch 2000;Eden and Willebrand 2001;Deshayes and Frankignoul 2008), a pure oceanic mode associated with advection of density anomalies (e.g., Delworth et al 1993;Jungclaus et al 2005), or a coupled atmosphere-ocean mode which in some models includes sea ice variability (e.g., Holland et al 2001;Bentsen et al 2004;Biastoch et al 2008).…”

Oceanic control of multidecadal variability in an idealized coupled GCM

“…By increasing the horizontal resolution up to 1°, the intrinsic atmospheric variability is enhanced and becomes significantly correlated to the MOC variability in cs96, with the NAM that leads by 2 years the MOC variability. This feature is common to many other numerical studies (Eden and Jung 2001;Deshayes and Frankignoul 2008;Gastineau and Frankignoul 2012), with a positive phase of the NAO that leads a maximum of MOC by few years. They describe the MOC variability in the North Atlantic as an oceanic response to stochastic atmospheric forcing.…”

“…A similar conclusion has been reached by Hodson and Sutton (2012) The atmospheric pattern correlated to the low-frequency oceanic variability is much more significant at higher resolution. Such a correlation is a robust feature of many high resolution realistic models (Eden and Willebrand 2001;Deshayes and Frankignoul 2008;Gastineau and Frankignoul 2012), with a positive phase of the NAO that occurs few years prior a MOC maximum. These studies describe the MOC variability in the Atlantic as an oceanic Fig.…”

An abrupt weakening of the subpolar gyre as trigger of Little Ice Age-type episodes

“…This hypothesis, however, found no support in a recent reconstruction of the AMOC strength (Rahmstorf et al 2015). Other studies suggested that the cold North Atlantic could have been associated with a shift in the phase of the North Atlantic Oscillation (NAO) (Trouet et al 2009;Copard et al 2012), as it is well known that the NAO influences the SPG variability through wind forcing and surface buoyancy fluxes (e.g., Eden and Willebrand 2001;Deshayes and Frankignoul 2008). The NAO reconstruction of Trouet et al 2009 was nevertheless contested in a later study Lehner et al (2012), and Ortega et al (2015) presented an alternative NAO reconstruction in which no phase shift was found between the MCA and LIA.…”