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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Apr 2018

Research article | 03 Apr 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Solar and volcanic forcing of North Atlantic climate inferred from a process-based reconstruction

Jesper Sjolte1, Christophe Sturm2, Florian Adolphi1,3, Bo M. Vinther4, Martin Werner5, Gerrit Lohmann5, and Raimund Muscheler1 Jesper Sjolte et al.
  • 1Department of Geology – Quaternary Science, Lund University, Sölvegatan 12, 223 62, Lund, Sweden
  • 2Department of Geological Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
  • 3Climate and Environmental Physics & Oeschger Centre for Climate Change Research, Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland
  • 4Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Oe, Denmark
  • 5Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Sciences, Postfach 12 01 61, 27515 Bremerhaven, Germany

Abstract. External forcings are known to impact atmospheric circulation. However, the analysis of the role of external forcings based on observational data is hampered due to the short observational period, and the sensitivity of atmospheric circulation to external forcings as well as persistence the effects are debated. A positive phase of the North Atlantic Oscillation (NAO) has been observed the following winter after tropical volcanic eruptions. However, past major tropical eruptions exceeding the magnitude of eruptions during the instrumental era could have more lasting effects. Decadal NAO variability has been suggested to follow the 11-year solar cycle, and linkages has been made between grand solar minima and negative NAO. However, the solar link to NAO found by modeling studies is not unequivocally supported by reconstructions, and is not consistently present in observations for the 20th century. Here we present a reconstruction of atmospheric winter circulation for the North Atlantic region covering the period 1241–1970 CE. Based on seasonally resolved Greenland ice core records and a 1200-year long simulation with an isotope enabled climate model, we reconstruct sea level pressure and temperature by matching the spatio-temporal variability of the modeled isotopic composition to that of the ice cores. This method allows us to capture the primary and secondary modes of atmospheric circulation in the North Atlantic region, while, contrary to previous reconstructions, preserving the amplitude of observed year-to-year atmospheric variability. Our results show 5 winters of positive NAO on average following major tropical volcanic eruptions, which is more persistent than previously suggested. In response to decadal minima of solar activity we find a high-pressure anomaly over Northern Europe, while a reinforced opposite response in pressure emerges with a 5-year time lag. On longer time scales we observe a similar response in circulation as for the 5-year time-lagged response. This is likely due to an increase in blocking frequency and an associated weakening of the subpolar gyre. The long-term response of temperature to solar minima shows cooling across Greenland, Iceland and Western Europe, resembling the cooling pattern during the Little Ice Age. While our results show a clear link between solar forcing and the secondary circulation patterns, we find no consistent relationship between solar forcing and NAO.

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Jesper Sjolte et al.
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Publications Copernicus
Short summary
Tropical volcanic eruptions and variations in solar activity have been suggested to influence the strength of westerly winds across the North Atlantic. We use Greenland ice core records and a climate model simulation, and find stronger westerly winds for 5 winters following tropical volcanic eruptions. We see a complex response to solar activity on different time scales. The long-term response to solar minima corresponds well to the cooling pattern during the period known as the Little Ice Age.
Tropical volcanic eruptions and variations in solar activity have been suggested to influence...