[P-EM17] 宇宙天気・宇宙気候

[PEM17-13] ¹⁴C during the ~660 BCE solar proton event from Japanese tree rings

★Invited Papers

*櫻井 敬久¹、三宅 芙沙²、門叶 冬樹¹、堀内 一穂³、宮原 ひろ子⁴、増田 公明²、大山 幹成⁵、坂本 稔⁶、光谷 拓実⁷、森谷 透¹ (1.山形大学理学部、2.名古屋大学宇宙地球環境研究所、3.弘前大学理工学研究科、4.武蔵野美術大学、5.東北大学植物園、6.国立歴史民俗博物館、7.国立奈良文化財研究所)

キーワード：放射性炭素、紀元前660年、太陽陽子

Annual rings record the intensity of cosmic rays that had entered into the Earth’s atmosphere. Several rapid ¹⁴C increases in the past, such as the 775 CE and 994CE ¹⁴C spikes, have been reported to originate from extreme solar proton events (SPEs). Another rapid ¹⁴C increase, also known as the ca. 660 BCE event in German oak tree rings as well as increases of ¹⁰Be and ³⁶Cl in ice cores, was presumed similar to the 775 CE event; however, as the ¹⁴C increase of approximately 10‰ in 660 BCE had taken a rather longer rise time of 3–4 years as compared to that of the 775 CE event, the occurrence could not be simply associated to an extreme SPE. In this study, to elucidate the rapid increase in ¹⁴C concentrations in tree rings around 660 BCE, we have precisely measured the ¹⁴C concentrations of earlywoods and latewoods inside the annual rings of Japanese cedar for the period 669–633 BCE. Based on the feature of ¹⁴C production rate calculated from the fine measured profile of the ¹⁴C concentrations using an 11-Box model of carbon cycle, we found that the ¹⁴C rapid increase occurred within 665–663.5 BCE, and that duration of ¹⁴C production describing the event is distributed from one month to 3.4 years. The possibility of occurrence of consecutive SPEs over up to three years is offered.