Recurrent Large‐Scale Solar Proton Events Before the Onset of the Wolf Grand Solar Minimum

• Published in: Geophysical research letters 2022-03, Vol.49 (5), p.n/a
• Main Authors: Miyahara, Hiroko, Tokanai, Fuyuki, Moriya, Toru, Takeyama, Mirei, Sakurai, Hirohisa, Ohyama, Motonari, Horiuchi, Kazuho, Hotta, Hideyuki
• Format: Article
• Language: English
• Subjects: Carbon; carbon‐14; extreme solar flares; grand solar minimum; Mass spectrometry; Mass spectroscopy; Protons; Solar activity; Solar cycle; solar dynamo; Solar flares; Solar minimum; solar proton events; Solar protons; Solar storms; Tree rings
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL097201

Carbon‐14 in tree rings have suggested there had been multiple extreme solar proton events (SPEs) in the past. While the largest events such as in 774–775 CE can be significantly detected by the typical precision of accelerator mass spectrometry, smaller but possibly more frequent events have been difficult to be detected. Thus, the frequency or any characteristics of such relatively smaller events are still largely unknown. In this paper, we report that large SPEs had occurred in 1261–1262, 1268–1269, and 1279–1280 CE before the onset of the Wolf minimum based on high‐precision carbon‐14 analyses. It is suggested that they had occurred at the maximum and the declining phase of solar cycles, and that they had occurred during the transition time of solar activity into a deep minimum. We propose that this episode may provide a unique opportunity to elucidate a potential interaction between the solar dynamo and extreme solar flares. Plain Language Summary The Sun is a magnetically active star and occasionally cause intense bursts that sometimes accompany the ejection of energetic protons, described as the solar proton events. In this paper, we report that there were three intense solar proton events in the thirteenth century, just before the onset of the Wolf grand minimum. We propose that these events may be related to the weakening of solar activity during that time. Key Points Multiple abrupt increases in carbon‐14 content were found during the transition time of solar activity into the grand minimum state They occurred at solar activity maximum or at the declining phase of solar cycles, suggesting that they originate from solar proton events The Wolf minimum may provide a unique opportunity to potentially deepen the understanding of the solar dynamo