A statistical study of the relationship between the solar cycle length andtree-ring index values

We have determined the correlation coefficient between tree-ring index valu es and the sunspot cycle length for 69 tree-ring data sets from around the world of greater than 594 years duration. A matrix of correlation coefficie nts is formed with varying delay and smoothing parameters. Similar matrices , formed from the same data, but randomly scrambled, provide a control agai nst which we can draw conclusions about the influence of the solar cycle le ngth on climate with a reasonable degree of confidence. We find that the da ta confirm an association between the sunspot cycle length and climate with a negative maximum correlation coefficient for 80% of the data sets consid ered. This implies that wider tree-rings (i.e. more optimum growth conditio ns) are associated with shorter sunspot cycles. Secondly, we find that the climatic effect of the solar cycle length is smoothed by several decades an d the degree of smoothing is dependent on the elevation and the geographica l location of the trees employed. Thirdly, we find evidence for a cyclic va riation of similar to 200 years period in either solar cycle length or tree ring index. (C) 1999 Elsevier Science Ltd. All rights reserved.