1. Reconstruction of the solar activity in 7th-11th centuries by the carbon 14 content in tree-rings F USA M IYAKE 1, K ENTARO N AGAYA 1, K IMIAKI M ASUDA 1, T OSHIO N AKAMURA 2 1 Solar-Terrestrial Environment Laboratory, Nagoya University 2 Center for Chronological Research, Nagoya University

2. Content Motivation Measurements (AD602-1072) Periodic analysis Summary

3. Motivation Sunspot measurement since AD 1610 Sunspot number changes periodically with 11-years on average （ Schwabe cycle ） We need to know much longer solar activity Measurement of a carbon-14 content in tree rings （ 14 C ； half-life…5730yr ）

4. Correlation of 14 C content and solar activity proton energetic CR Atmospheric molecule neutron 14 N 14 C 14 CO 2 High solar magnetic activity →Low cosmic ray flux to the Earth CR collide with atmospheric molecule →various nuclides （ Nitrogen captures a neutron and 14 C is produced ） 14 C content in tree rings is retained for record of the past CR intensity and Solar activity 14 C is oxidized to form 14 CO 2 and taken by trees during the carbon cycle

5. measurement periods was mainly in the grand solar minima (Nagoya) →Solar cycle （ Schwabe cycle ） is not constant at 11-yr →14yr in Maunder minimum …Miyahara et al. （ 2004 ） Solar cycle length in the normal solar activity? ← ＩＮＴＣＡＬ （ 14 Ｃ calibration curve ） Time resolution 10yr ←STEL Nagoya Univ. Time resolution 1-2yr Previous studies Maunder -1000 010002000 -20 0 20 AD Δ14C ‰

6. Measurements ・ 2 periods was measured previously (pink lines) ・ measurement with 2-year resolution Period of normal solar activity (include weak solar min.) AD 602 to 1072 Weak solar min. KuwanaMenjo

7. Sample preparation Chemical cleaning Extract alpha-cellulose which doesn’t move between rings slice Each ring was separated by a cutter knife To CO 2 Cellulose is combusted to CO 2 at 850 ℃ purification CO 2 was purified with cold trap graphitize CO 2 is graphitized by hydrogen reduction measurement 14 C content in graphite is measured by the AMS at Nagoya University (average error; 2.6‰) neutralization sodium chlorite ＮａＯＨ ＨＣ ｌ ultrasonic cleaning Accelerator Mass Spectrometor (AMS) at Nagoya University Japanese cedar tree About 2000-yr-old Purification vacuum line We can measure 30 samples in each measurement run It takes about one month for sample preparation

8. Comparison with IntCal98 The present biennialy data were averaged to obtain the same time resolution as that of IntCal IntCal used North American and European trees →difference might be due to the regional effect

9. For periodic analysis There are gaps (increased in some years) → eliminate these effects A series after the correction

10. Fourier analysis Time structure of these two periods? Apply a wavelet transform → both time and frequency components can be obtained 11.014.3 Predominant periods of 11yr and 14yr （ >99% ） →Solar Schwabe cycle 99% 95%

11. Wavelet analysis Result of wavelet analysis → the periods of 11yr and 14yr are not continuous Various periods may appear due to the errors Wavelet transform is more susceptible to measurement errors than Fourier transform % 11yr 14yr

12. Weak solar minimum 13.1yr 10.0yr % 650750 Max Min 10 13.1 Including Max+Min AD602-770 13.6 Including Min AD650-770 10.2 Became 13 years at weak solar minimum (AD650-720)

13. Conclusion We measured 14 C content in tree rings from AD602 to 1072 IntCal and present series are almost consistent We detected predominant of 11 year & 14 year periods by Fourier analysis (>99%) These periods were not detected continuously by wavelet analysis There are possibilities of longer periods in the weak solar activity minimum (650-720AD) Wavelet transform is more susceptible to measurement errors than Fourier transform → We will measure 14 C content with higher accuracy to find clear periodicities

14. We need old trees Do you have old trees? Or do you know where old trees are? If you know about that, please tell us. We want to measure 14 C content in trees from all over the world. Contact: fmiyake@stelab.nagoya-u.ac.jp