Here, using the natural orthogonal composition (NOC) technique,
we investigate the emergence of spatio-temporal complexity
in the 11-year solar cycle, as monitored by the sunspot
area butterfly diagram. By applying a 2nd order complexity measure
(Shiner et al. 1999), we show that spatio-temporal and/or
dynamical complexity is an intrinsic property of the solar cycle,
and that the long-term evolution of solar cycle activity seems to
point towards a more regular (less complex) behavior.
The paper is organized as follows. Section 2 provides a brief
introduction to the NOC technique. In Sect. 3, we describe the
data set and results from the NOC analysis, the study of the
chaotic and spectral features of the principal components (PCs).
In particular, we pay attention to the first two PCs by comparing
their phase portrait with that coming from a stochastic version
of a Lotka-Volterra predator-prey model. In this section, we
also show the occurrence of dynamical complexity obtained by
the application of information theory descriptors. In Sect. 4, we
summarize our findings and draw conclusions.