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Several globally synchronous spikes in radiocarbon production have now been detected in known-age tree-ring archives. Such occurrences, commonly known a Miyake events, must have been prompted by enormous bursts of cosmic radiation. Extreme storms on the Sun are widely believed to be the ultimate source of this radiation. Indeed, the phenomena are expected to be akin to scaled-up versions of modern ground level enhancements (GLEs). Usoskin and Kovaltsov (2021) attempted to relate GLEs to Miyake events by way of a best-fit Weibull distribution with a sharp roll-oX, knowing that a simple power law extrapolation would not connect the two groups. Although this function appears convincing, a large gap is left between the most intense GLEs and the weakest Miyake events. This vacancy is thought to represent the region in which ‘intermediate- sized’events, currently missing from the observational record, should be positioned. One means of finding such events might be to measure the historical radiocarbon record at ever higher precision. By applying this approach to Japanese asunaro tree rings, Miyahara et al. (2022) claim to have identified three such intermediate-sized events in the 13th century CE. In this study, we attempt to replicate these findings by making similarly high precision measurements on European oak over exactly the same calendar years.
Usoskin, I. G. and Kovaltsov, G. A. 2021. Mind the gap: new precise 14C data indicate the nature of extreme solar particle events. Geophysical Research Letters 48: e2021GL094848. https://doi.org/10.1029/2021GL094848
Miyahara, H., Tokanai, F., Moriya, T., Takeyama, M., Sakurai, H., Ohyama, M., Kazuho, H., and Hideyuki H. 2022. Recurrent large-scale solar proton events before the onset of the Wolf grand solar minimum. Geophysical Research Letters 49: 2021GL097201. https://doi.org/10.1029/2021GL097201