Figures 3 and 4 show the first six EOFs and the corresponding
PCs. These functions provide, respectively, the latitudinal
dependence (EOF → φk(θ)) and the time variation (PC → Ak
(t))
in the modes, ordered according to the eigenvalue spectrum λk.
Looking at the structures of the EOFs, one can immediately note
the inherent symmetry of these EOFs. This is particularly evident
for the EOFs with k = 1, 2, which are symmetric with
respect to the equator (even-parity), thus resembling the symmetry
observed in the butterfly diagram. In contrast, the EOF with
k = 3 is antisymmetric (odd-parity) with respect to the equator.
The symmetry features are less evident with increasing k
and may take into account the so-called north-south asymmetries
(Sokoloff & Nesme-Ribes 1994). We note that, although all
of the features of the PCs seem to be characterized by a nearly
cyclic behavior resembling the solar activity cycle, they have different
intermittency degrees. We find that the kurtosis excess κ,
which indicates the deviation from Gaussianity, is κ ∼ 3 and
κ > 7 for the first two PCs and for the remainder, respectively.