Journal ArticleDOI
Natural forcing of climate during the last millennium: fingerprint of solar variability
Didier Swingedouw,Laurent Terray,Christophe Cassou,Aurore Voldoire,D. Salas-Mélia,Jérôme Servonnat +5 more
TLDR
In this paper, the authors used a state-of-the-art climate model to simulate the last millennium and found that modelled variations of surface temperature in the Northern Hemisphere are coherent with existing reconstructions.Abstract:
The variability of the climate during the last millennium is partly forced by changes in total solar irradiance (TSI). Nevertheless, the amplitude of these TSI changes is very small so that recent reconstruction data suggest that low frequency variations in the North Atlantic Oscillation (NAO) and in the thermohaline circulation may have amplified, in the North Atlantic sector and mostly in winter, the radiative changes due to TSI variations. In this study we use a state-of-the-art climate model to simulate the last millennium. We find that modelled variations of surface temperature in the Northern Hemisphere are coherent with existing reconstructions. Moreover, in the model, the low frequency variability of this mean hemispheric temperature is found to be correlated at 0.74 with the solar forcing for the period 1001–1860. Then, we focus on the regional climatic fingerprint of solar forcing in winter and find a significant relationship between the low frequency TSI forcing and the NAO with a time lag of more than 40 years for the response of the NAO. Such a lag is larger than the around 20-year lag suggested in other studies. We argue that this lag is due, in the model, to a northward shift of the tropical atmospheric convection in the Pacific Ocean, which is maximum more than four decades after the solar forcing increase. This shift then forces a positive NAO through an atmospheric wave connection related to the jet-stream wave guide. The shift of the tropical convection is due to the persistence of anomalous warm SST forcing the anomalous precipitation, associated with the advection of warm SST by the North Pacific subtropical gyre in a few decades. Finally, we analyse the response of the Atlantic meridional overturning circulation to solar forcing and find that the former is weakened when the latter increases. Changes in wind stress, notably due to the NAO, modify the barotropic streamfunction in the Atlantic 50 years after solar variations. This implies a wind-driven modification of the oceanic circulation in the Atlantic sector in response to changes in solar forcing, in addition to the variations of the thermohaline circulation.read more
Citations
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Journal ArticleDOI
External forcing as a metronome for Atlantic multidecadal variability
TL;DR: Instrumental records, proxy data and climate modelling show that multidecadal variability is a dominant feature of North Atlantic sea-surface temperature variations as discussed by the authors, and that the timing of this variability is determined mainly by external forcing, for example from volcanic eruption or solar forcing.
Journal ArticleDOI
The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability
TL;DR: In this paper, the authors presented two new multi-proxy reconstructions of the extra-tropical Northern Hemisphere (30-90° N) mean temperature: a two-millennia long reconstruction reaching back to 1 AD and a 500-yr long reconstruction reached back to 1500 AD.
Journal ArticleDOI
Bi-decadal variability excited in the coupled ocean–atmosphere system by strong tropical volcanic eruptions
Davide Zanchettin,Claudia Timmreck,H. F. Graf,Angelo Rubino,Stephan Lorenz,Katja Lohmann,Kirstin Krüger,Johann H. Jungclaus +7 more
TL;DR: In this article, the authors provide a physically consistent theoretical framework to interpret decadal Northern Hemisphere (NH) regional winter climates variability during the last millennium, particularly involving interactions between the Atlantic meridional overturning circulation and the North Atlantic gyre circulation.
Journal ArticleDOI
North Atlantic storminess and Atlantic Meridional Overturning Circulation during the last Millennium: Reconciling contradictory proxy records of NAO variability
TL;DR: In this paper, the authors review proxy evidence for two alternative hypotheses for the effects of this shift in the North Atlantic region and reconcile the two competing hypotheses based on available results from climate model simulations of the last Millennium.
Journal ArticleDOI
Small influence of solar variability on climate over the past millennium
TL;DR: In this paper, an analysis of numerical simulations and climate reconstructions suggests that the amplitude of solar forcing was small over this interval, with the main climate forcing derived from volcanic eruptions and greenhouse gas concentrations.
References
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Journal ArticleDOI
Decadal Trends in the North Atlantic Oscillation: Regional Temperatures and Precipitation
TL;DR: An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.
Book Chapter
Changes in Atmospheric Constituents and in Radiative Forcing
Piers M. Forster,Venkatachalam Ramaswamy,Paulo Artaxo,Terje Koren Berntsen,Richard Betts,David W. Fahey,Jim Haywood,Judith Lean,David C. Lowe,Gunnar Myhre,John Nganga,Ronald G. Prinn,Graciela B. Raga,Michael Schulz,Rob van Dorland,Greg Bodeker,Oliver Boucher,William D. Collins,T.J. Conway,Edward J. Dlugokencky,James W. Elkins,David Etheridge,P. Foukal,Paul J. Fraser,Marvyn Geller,Fortunat Joos,Charles D. Keeling,Stefan Kinne,K. Lassey,Ulrike Lohmann,Andrew C. Manning,S. A. Montzka,David E. Oram,K. O'Shaughnessy,S. Piper,Gian-Kasper Plattner,Michael Ponater,Navin Ramankutty,G. Reid,David Rind,Karen H. Rosenlof,Robert Sausen,D. Schwarzkopf,S.K. Solanki,Garry Stenchikov,N. Stuber,Toshihiko Takemura,Christiane Textor,R. Wang,Ray F. Weiss,T. Whorf +50 more
Journal ArticleDOI
The Arctic oscillation signature in the wintertime geopotential height and temperature fields
TL;DR: The Arctic Oscillation (AO) as mentioned in this paper is the signature of modulations in the strength of the polar vortex aloft, and it resembles the NAO in many respects; but its primary center of action covers more of the Arctic, giving it a more zonally symmetric appearance.
Journal ArticleDOI
Isopycnal mixing in ocean circulation models
TL;DR: In this paper, a subgrid-scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non-eddy-resolving ocean circulation models.
Climatological atlas of the world ocean
TL;DR: A project to objectively analyze historical ocean temperature, salinity, oxygen, and percent oxygen saturation data for the world ocean has recently been completed at the National Oceanic and Atmospheric Administration's (NOAA) Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey.