The chaotic solar cycle

I. Analysis of cosmogenic -data

A. Hanslmeier¹ and R. Brajša²

¹ Inst. für Physik, Geophysik Astrophysik und Meteorologie, Univ.-Platz 5, 8010 Graz, Austria e-mail: arnold.hanslmeier@uni-graz.at
² Hvar Observatory, Faculty of Geodesy, University of Zagreb, Kačićeva 26, 10000 Zagreb, Croatia e-mail: romanb@geof.hr

Received: 9 August 2009
Accepted: 18 September 2009

Abstract

Context. The study of solar activity over long time intervals using proxies.

Aims. The periodicity of the solar activity cycle is studied. The solar activity cycle is governed by a complex dynamo mechanism. Methods of nonlinear dynamics enable us to learn more about the regular and chaotic behavior of solar activity.

Methods. By applying methods of nonlinear dynamics, the solar activity cycle is studied by using solar activity proxies that have been reaching into the past for over 10 000 years. The complexity of the system is expressed by several parameters of nonlinear dynamics, such as embedding dimension or false nearest neighbors, and the method of delay coordinates is applied to the time series.

Results. The solar activity cycle is found to be on the edge of chaotic behavior. This can explain the observed intermittent period of longer lasting solar activity minima. Filtering the data by eliminating variations below a certain period (the periods 380 yr and 57 yr were used) yields a far more regular behavior of solar activity.

Conclusions. The solar time series of solar activity proxies used here clearly shows that solar activity behaves differently from random data. The unfiltered data exhibit a complex dynamics requiring an embedding dimension >15. The variations become more regular when filtering the data. The results also indicate that solar activity proxies are influenced by other than solar variations and reflect solar activity only on longer time scales.