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

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First spotted in tree rings, ice-core evidence for AD 774/775 and 993/994 cosmic-ray events points to the sun:

 

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.

 

Open Access

 

http://www.nature.com/ncomms/2015/151026/ncomms9611/full/ncomms9611.html