Search

Radiocarbon (14C) is produced in the upper atmosphere by galactic cosmic rays, which are modulated by solar magnetic activity. Its content in tree rings is retained and provides a record of past cosmic ray intensity and solar activity. We have measured the 14C content in Japanese cedar tree rings from AD 600 to 760, a time interval that includes a grand solar minimum in the 7th century, with a resolution of 2 year. Periodicity analysis of the 14C data shows that there is a component in the frequency band of the Schwabe cycle, with a period of 12-13 years continuing throughout the minimum. This is the fourth case in which an increase in the length of the Schwabe cycle has been observed in a grand solar minimum, after the Maunder Minimum, the Spörer Minimum，and the 4th century BC Minimum. In addition to the increase in the cycle length, it was also found that short frequency components appear in preceding and the beginning of the minimum. It is possible that this short component is related to the solar dynamo., 名古屋大学年代測定総合研究センターシンポジウム報告