993–994 carbon-14 spike
The 993–994 carbon-14 spike was a rapid increase in carbon-14 content from tree rings, and followed the 774–775 carbon-14 spike. This event is also confirmed by a sharp increase of beryllium-10 and hence considered as solar-origin.  It may have come from a massive solar storm as a series of auroral observations are known to be observed in late 992. 
- Miyake, F.; et al. (2013). "Another rapid event in the carbon-14 content of tree rings : Nature Communications : Nature Publishing Group". Nature Communications. 4: 1748. doi:10.1038/ncomms2783. PMID 23612289.
- Mekhaldi, F.; et al. (2015). "Multiradionuclide evidence for the solar origin of the cosmic-ray events of ᴀᴅ 774/5 and 993/4 : Nature Communications : Nature Publishing Group". Nature Communications. 6: 8611. doi:10.1038/ncomms9611. PMC 4639793. PMID 26497389.
- Hayakawa, H.; et al. (2017). "Historical Auroras in the 990s: Evidence of Great Magnetic Storms : Solar Physics : Springer". Solar Physics. 292. arXiv:1612.01106. doi:10.1007/s11207-016-1039-2.
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