ATMOSPHERIC CARBON DIOXIDE AND RADIOCARBON: I 



63 



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 < 



a 



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cr 



cr 



w +20 



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+40 



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 1700 



J I I L 



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j i L 



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1750 



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1850 



1900 



DATE 



1950 



Fig. 8 Record of solar activity expressed by the sunspot numbers of 

 Schove 1 7 compared with the ' 4 C content of wood samples dated by ring 

 counts. Both records have been averaged over periods covering the intervals 

 between solar minimums. The sunspot record has been inverted. 



Furthermore, direct observations at recent solar-activity extremes indicate an 

 inverse correlation of sunspot numbers and cosmic-rav intensitv. From these 

 data Lingenfelter 1 8 and Lingenfelter and Ramaty 19 have derived a linear 

 relation between observed sunspot number and the global average 1 C 

 production in the atmosphere on the basis of an analysis of the production of 

 C by cosmic rays. We attempt to establish in this and the succeeding paper 

 how much such a modulation can interfere with estimates of the Suess effect. 



Schove observed that a fundamental 11 -year cycle in sunspot activity is 

 modulated by a slower cycle with a frequency of the order of 1/78 year -1 . A 

 power spectrum of the sunspot (Wolf) numbers for the period 1700 to 1950 

 (Fig. 9) further reveals upper and lower modulation side bands at frequencies of 

 approximately (1/11 ±1/80) year" 1 and (1/11 ±2/80) year -1 . These are a 

 general consequence of a nonlinear modulation of the higher frequency by the 

 lower (actually centered at a period of about 85 years). Since the sunspot 

 number returns to an almost constant value during years of minimum solar 

 activity, the principal features of the sunspot record since 1700 are represented 

 by the function (Fig. 10) 



S(t) = Ci + (C 2 + C 3 sin 27r/ m t)(l + sin 27r/„t) 



(1) 



