are identifiable for k below and above k = 3. In particular, the
first eigenvalue is larger by 4 times than the second, and 5 times
than the third. The other eigenvalues monotonically decrease for
increasing k, exhibiting a cut-off for k > 18. Because this spectrum
can be considered as the equivalent of an energy spectrum,
and is associated with the variance of the various components,
we can assume that most of the variability observed in the solar
cycle can be explained in terms of a very small number of
components (n ≤ 3).