Research Note: Nonlinear time series analysis of northern and southern solar hemisphere daily sunspot numbers in search of short-term chaotic behavior

¹ Physics Department, University of Connecticut, 2152 Hillside Rd U-3046, Storrs, CT 06269-3046, USA e-mail: nj@phys.uconn.edu
² Physics Department, Ursinus College, PO Box 1000, Collegeville, PA 19426-1000, USA e-mail: ccellucci@ursinus.edu

Corresponding author: J. S. Schweitzer, schweitz@phys.uconn.edu

Received: 19 April 2001
Accepted: 11 September 2001

Abstract

Daily sunspot number data for the northern and southern solar hemispheres from 22 cycle maximum to the current cycle 23 maximum are analyzed using nonlinear time series methods in an effort to identify chaotic behavior on short time scales as indicated by the recent helioseismic observations. We find that separate analyses of north and south solar hemisphere data provide more consistent results. Different behavior at maxima and minimum are observed. The maximum sections have a region that bears the marks of self-similarity whereas the minimum shows no such behavior. However, it is the minimum data that determine the results for the correlation dimension over one cycle. Thus, over many cycles, minima mask the potentially self-similar sections at maximum; access to information on whether the solar cycle is chaotic long-term is severely limited, if not precluded. To make sure the results were not affected by noise, the method of artifactual correlations was used to investigate the noise content of the data, indicating that both the north and south data sets were relatively free of additive noise.