University of Oulu

Uusitalo, J., Arppe, L., Hackman, T., Helama, S., Kovaltsov, G., Mielikäinen, K., Mäkinen, H., Nöjd, P., Palonen, V., Usoskin, I., Oinonen, M. (2018) Solar superstorm of AD 774 recorded subannually by Arctic tree rings. Nature Communications, 9, 3495. doi:10.1038/s41467-018-05883-1

Solar superstorm of AD 774 recorded subannually by Arctic tree rings

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Author: Uusitalo, J.1,2; Arppe, L.1; Hackman, T.2;
Organizations: 1Finnish Museum of Natural History, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland
2Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland
3Natural Resources Institute Finland, Eteläranta 55, 96300 Rovaniemi, Finland
4Ioffe Physical-Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg, Russia
5Natural Resources Institute Finland, Tietotie 2, 02150 Espoo, Finland
6Space Climate Research Unit and Sodankylä Geophysical Observatory, University of Oulu, Pentti Kaiteran katu 1, 90014 Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.2 MB)
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Language: English
Published: Springer Nature, 2018
Publish Date: 2018-08-28


Recently, a rapid increase in radiocarbon (¹⁴C) was observed in Japanese tree rings at AD 774/775. Various explanations for the anomaly have been offered, such as a supernova, a γ-ray burst, a cometary impact, or an exceptionally large Solar Particle Event (SPE). However, evidence of the origin and exact timing of the event remains incomplete. In particular, a key issue of latitudinal dependence of the ¹⁴C intensity has not been addressed yet. Here, we show that the event was most likely caused by the Sun and occurred during the spring of AD 774. Particularly, the event intensities from various locations show a strong correlation with the latitude, demonstrating a particle-induced ¹⁴C poleward increase, in accord with the solar origin of the event. Furthermore, both annual ¹⁴C data and carbon cycle modelling, and separate earlywood and latewood ¹⁴C measurements, confine the photosynthetic carbon fixation to around the midsummer.

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Series: Nature communications
ISSN: 2041-1723
ISSN-E: 2041-1723
ISSN-L: 2041-1723
Volume: 9
Article number: 3495
DOI: 10.1038/s41467-018-05883-1
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: The work has been supported by the Academy of Finland (grants 251287, 251441, 288083, 288267, 292788 and 272157/ReSoLVE Centre of Excellence).
Academy of Finland Grant Number: 272157
Detailed Information: 272157 (Academy of Finland Funding decision)
Dataset Reference: Electronic supplementary material
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