A Study of Variation of the 11-yr Solar Cycle before the onset of the Spoerer Minimum based on Annually measured 14C Content in tree Rings

Proxy-based observations of solar activity in the past have revealed long-term variations, such as the Gleissberg cycle (~88 yr), de Vries cycle (~200 yr), and the Hallstatt cycle (~2000 yr). Such long-term variations of solar activity sometimes cause the disappearance of sunspots for several decade...

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Bibliographic Details
Published in:Radiocarbon 2019-12, Vol.61 (6), p.1749-1754
Main Authors: Moriya, Toru, Miyahara, Hiroko, Ohyama, Motonari, Hakozaki, Masataka, Takeyama, Mirei, Sakurai, Hirohisa, Tokanai, Fuyuki
Format: Article
Language:eng ; jpn
Subjects:
Cellulose
Cosmic rays
Graphite
Solar activity
Solar cycle
Solar physics
Sunspots
Tree rings
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Summary:Proxy-based observations of solar activity in the past have revealed long-term variations, such as the Gleissberg cycle (~88 yr), de Vries cycle (~200 yr), and the Hallstatt cycle (~2000 yr). Such long-term variations of solar activity sometimes cause the disappearance of sunspots for several decades. Currently, solar activity is becoming weaker, and there is a possibility that another long-term sunspot minimum could occur. However, the detailed mechanism of the weakening in solar activity is unknown, and the prediction of solar activity is ambiguous. In this study, we investigate the transitions of solar cycle length before the onset of the Spoerer Minimum, the longest grand minimum in the past 2000 yr. We measured the 14C content in an asunaro tree (Thujopsis dolabrata) excavated at Shimokita Peninsula from 1368–1420 CE using the compact AMS system at Yamagata University. It is found that the solar cycle lengthened to be 14–16 yr from 2 cycles before the onset of the Spoerer Minimum.
ISSN:0033-8222
1945-5755
DOI:10.1017/RDC.2019.123