The signature of low‐frequency oceanic forcing in the Atlantic Multidecadal Oscillation

O’Reilly, Christopher H.; Huber, Markus; Woollings, Tim; Zanna, Laure

doi:10.1002/2016gl067925

Cited by 107 publications

(145 citation statements)

References 34 publications

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“…It is likely that atmosphere-ocean coupling plays a role in decadal variability in the North Atlantic sector (e.g., O'Reilly et al 2016). For example, Woollings et al (2015) found that decadal jet speed variability in a highresolution climate model was consistent with driving from subpolar gyre SST anomalies.…”

Section: Discussionmentioning

confidence: 99%

Daily to Decadal Modulation of Jet Variability

et al. 2018

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The variance of a jet's position in latitude is found to be related to its average speed: when a jet becomes stronger, its variability in latitude decreases. This relationship is shown to hold for observed midlatitude jets around the world and also across a hierarchy of numerical models. North Atlantic jet variability is shown to be modulated on decadal time scales, with decades of a strong, steady jet being interspersed with decades of a weak, variable jet. These modulations are also related to variations in the basinwide occurrence of highimpact blocking events. A picture emerges of complex multidecadal jet variability in which recent decades do not appear unusual. An underlying barotropic mechanism is proposed to explain this behavior, related to the change in refractive properties of a jet as it strengthens, and the subsequent effect on the distribution of Rossby wave breaking.

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Section: Discussionmentioning

confidence: 99%

Daily to Decadal Modulation of Jet Variability

et al. 2018

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“…Clement et al (2015) argue that stochastic forcing from the atmosphere is the main source for the AMV, without any role for changes in ocean heat transport. Their article has attracted considerable attention, leading to several studies opposing their view (e.g., O'Reilly et al 2016;Zhang et al 2016;Drews and Greatbatch 2016).…”

Section: Introductionmentioning

confidence: 99%

Evolution of the Atlantic Multidecadal Variability in a Model with an Improved North Atlantic Current

Drews

Greatbatch

2017

J. Climate

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This article investigates the dynamics and temporal evolution of the Atlantic multidecadal variability (AMV) in a coupled climate model. The model contains a correction to the North Atlantic flow field to improve the path of the North Atlantic Current, thereby alleviating the surface cold bias, a common problem with climate models, and offering a unique opportunity to study the AMV in a model. Changes in greenhouse gas forcing or aerosol loading are not considered. A striking feature of the results is the contrast between the western and eastern sides of the subpolar gyre in the model. On the western side, anomalous heat supply by the ocean plays a major role, with most of this heat being given up to the atmosphere in the warm phase, largely symmetrically about the time of the AMV maximum. By contrast, on the eastern side, the ocean anomalously gains heat from the atmosphere, with relatively little role for ocean heat supply in the years before the AMV maximum. Thereafter, the balance changes with heat now being anomalously removed from the eastern side by the ocean, leading to a reduced ocean heat content, behavior associated with the establishment of an intergyre gyre at the time of the AMV maximum. In the warm phase, melting sea ice leads to a freshening of surface waters northeast of Greenland that travel southward into the Irminger and Labrador Seas, shutting down convection and terminating the AMV warm phase.

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“…Variability in the Atlantic meridional overturning circulation (AMOC) has been linked to variability in Atlantic sea surface temperatures and associated climate impacts (Kushnir 1994;Delworth and Mann 2000;Knight et al 2005;O'Reilly et al 2016). There has been a significant number of studies aimed at understanding model-simulated AMOC variability in preindustrial or current climate conditions (Delworth et al 1993;Greatbatch and Zhang 1995;Yeager and Danabasoglu 2012); see also the recent review by Buckley and Marshall (2016).…”

Section: Introductionmentioning

confidence: 99%

Suppression of Atlantic Meridional Overturning Circulation Variability at Increased CO2

2016

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Multidecadal variability in the Atlantic meridional overturning circulation (AMOC) is shown to differ significantly between the 4 3 CO 2 and preindustrial control simulations of the GFDL Earth System Model, version 2M (ESM2M) general circulation model (GCM). In the preindustrial simulation, this model has a peak in the power spectrum of both AMOC and northward heat transport at latitudes between 268 and 508N. In the 4 3 CO 2 simulation, the only significant spectral peak is near 608N. Understanding these differences is important for understanding the effect of future climate change on climate variability, as well as for providing insight into the physics underlying AMOC variability. Transfer function analysis demonstrates that the shift is predominantly due to a shift in the internal ocean dynamics rather than a change in stochastic atmospheric forcing. Specifically, the reduction in variance from 268 to 458N is due to an increased stratification east of Newfoundland that results from the shallower and weaker mean overturning. The reduced AMOC variance that accompanies the reduced mean value of the AMOC at 4 3 CO 2 differs from predictions of simple box models that predict a weaker circulation to be closer to a stability bifurcation point and, therefore, be accompanied by amplified variability. The high-latitude variability in the 4 3 CO 2 simulation is related to the advection of anomalies by the subpolar gyre, distinct from the variability mechanism in the control simulation at lower latitudes. The 4 3 CO 2 variability has only a small effect on midlatitude meridional heat transport, but does significantly affect sea ice in the northern North Atlantic.

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The signature of low‐frequency oceanic forcing in the Atlantic Multidecadal Oscillation

Cited by 107 publications

References 34 publications

Daily to Decadal Modulation of Jet Variability

Daily to Decadal Modulation of Jet Variability

Evolution of the Atlantic Multidecadal Variability in a Model with an Improved North Atlantic Current

Suppression of Atlantic Meridional Overturning Circulation Variability at Increased CO2

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