Multiradionuclide evidence for the solar origin of the cosmic-ray events of AD 774/5 and 993/4

Florian Mekhaldi (), Raimund Muscheler, Florian Adolphi, Ala Aldahan, Jürg Beer, Joseph R. McConnell, Göran Possnert, Michael Sigl, Anders Svensson, Hans-Arno Synal, Kees C. Welten and Thomas E. Woodruff
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Florian Mekhaldi: Lund University
Raimund Muscheler: Lund University
Florian Adolphi: Lund University
Ala Aldahan: United Arab Emirates University
Jürg Beer: Swiss Federal Institute of Aquatic Science and Technology
Joseph R. McConnell: Desert Research Institute
Göran Possnert: Tandem Laboratory, Uppsala University
Michael Sigl: Desert Research Institute
Anders Svensson: Center for Ice and Climate, Niels Bohr Institute, University of Copenhagen
Hans-Arno Synal: Laboratory of Ion Beam Physics, ETH Zürich
Kees C. Welten: Space Sciences Laboratory, University of California
Thomas E. Woodruff: PRIME Laboratory, Purdue University

Nature Communications, 2015, vol. 6, issue 1, 1-8

Abstract: Abstract The origin of two large peaks in the atmospheric radiocarbon (14C) concentration at AD 774/5 and 993/4 is still debated. There is consensus, however, that these features can only be explained by an increase in the atmospheric 14C production rate due to an extraterrestrial event. Here we provide evidence that these peaks were most likely produced by extreme solar events, based on several new annually resolved 10Be measurements from both Arctic and Antarctic ice cores. Using ice core 36Cl data in pair with 10Be, we further show that these solar events were characterized by a very hard energy spectrum with high fluxes of solar protons with energy above 100 MeV. These results imply that the larger of the two events (AD 774/5) was at least five times stronger than any instrumentally recorded solar event. Our findings highlight the importance of studying the possibility of severe solar energetic particle events.

Date: 2015
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DOI: 10.1038/ncomms9611

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