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Published online by Cambridge University Press: 25 April 2016
Four tree ring-index site chronologies, representing standardised annual growth rates for spruce trees growing at high altitude sites in Colorado, have been employed as proxy data in a regression model for the annual variation of solar radio flux at 2800 MHz (F 10·7) and the Catania sunspot area (A c). These dendrochronological time series all exhibit significant power spectrum peaks at about 11 years and separately correlate with the annual values of R z, F 10·7 and A c, as solar activity indicators. The two models constructed give the cyclic variation of F 10·7 and A c back to AD1673.