A SEARCH FOR CHAOTIC BEHAVIOR IN SOLAR-ACTIVITY

We present an analysis of the behaviour of solar activity and look for the presence of low-dimensional deterministic chaos within it. The or iginal databases for such analysis have been the daily sunspot number (1818-1990) and daily sunspot areas(1874-1989) from which we have cons tructed twenty different data sets, raw and filtered, displaying the s olar and magnetic cycle. We have used the Grassberger-Procaccia algori thm to compute the correlation dimension which, also, has allowed us t o obtain the K-2 entropy and, for some time series, the maximum Lyapun ov exponent has also been computed. Our results show that in none of t he twenty time series considered does evidence appear of chaotic behav iour, since there is no saturation of the correlation dimension with t he embedding dimension and the K-2 entropy shows a divergent behaviour . A study of previous works which claim this kind of behaviour to be p resent in solar activity suggests that such a conclusion has been deri ved from very short scaling regions obtained using low time delays in the computations of the correlation dimension. The behaviour of solar cycle, with periods of low activity, suggests the presence of determin istic chaos and some of its features can be reproduced by means of sim ple nonlinear dynamo models. However, it seems that for an unambiguous detection of such behaviour, from solar activity data or proxy record s, we will have to wait for the availability of longer and reliable da ta sets covering the periods of reduced activity.