Variation of solar activity during the Maunder Minimum deduced from radiocarbon content in tree rings(Proceedingsof the 17^<th> Symposium on Researches Using the Tandetron AMS System at Nagoya University in 2004)

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  • 樹木年輪中^<14>Cで探るマウンダー極小期の太陽活動変動(第17回名古屋大学タンデトロン加速器質量分析計シンポジウム平成16(2004)年度報告)

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Abstract

This paper presents the variation of solar activity during the Maunder Minimum (1645-1715 AD) deducted from radiocarbon content in tree-rings. Radiocarbon is produced by the galactic cosmic rays, which are modulated by the solar wind and the interplanetary magnetic field in the heliosphere. The production rate of radiocarbon, therefore, reflects the state of solar magnetic activity. Most distinct index of solar magnetic activity it the group sunspot number. The variations of sunspot number have shown clear cyclicity since the 18^<th> century with average length being about eleven years. The sunspots, however, have once almost disappeared during the period of 1645-1715 AD due to extraordinary weakening of solar activity. This period has been called as the Maunder Minimum. There is no remarkable cyclicity in the sunspot variations. We, therefore, investigated the cyclicity of radiocarbon content in tree rings from the Maunder Minimum in order to clarify the characteristics of solar activity during this period. We compared two radiocarbon records obtained newly by our group and by Stuiver et al. The results of frequency analyses have shown that solar magnetic reversals had maintained through the Maunder Minimum and that the length of the "eleven-year" cycle was stretched to 13-15 years.

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