A REGRESSION-MODEL DERIVED FROM PROXY DATA FOR THE 11-YEAR SOLAR-CYCLE

Ring-width time series obtained from Engelmann Spruce trees growing at high altitude sites in the Rocky Mountains, Colorado, exhibit dominan t 11-year spectral periodicities. A significant linear cross-correlati on also exists between these series and the Zurich series of annual su nspot numbers. A regression model based on these proxy data has been d eveloped for the annual variation of the 11-year solar cycle. It is es tablished that over the calibration period a very high percentage of t he variance (40%) in growth patterns, contributed by a single source, can be explained by solar variation. The model correlates with the Zur ich series of sunspot numbers at the 99% significance level post 1870 AD. However, over the total period 1700-1870 AD the comparison was fou nd to be not statistically significant at lag 0. Some possible reasons for this are considered.