Abstract:
We present results of the fast Fourier transform
(FFT), the MEM analysis, and the wavelet analysis (WA),
of the temporal variation of the monthly disk integrated
“CaII-K plage-area and enhanced network (EN) area” hereafter called ‘plage index’ derived by Tlatov et al. (2009),
from spectro-heliograms taken in Ca II K line at Kodaikanal
Observatory, from February 1907 to April, 1998, In the
range >3 months and < decade, the Fourier transform
power spectra reveal solar cycle periodicity ∼122 months,
its sub-harmonic ∼61 months, two short quasi-periodicities
(>2 and <4 months), and nine ‘intermediate-range’ quasiperiodicities ( 4 mo and <11 yr), in the variation of the
plage index. The quasi-periodicities include Rieger, Rieger
type and quasi-biennial. The presence of quasi-periodicities
and the mean values of the periods are confirmed by the
maximum entropy method (MEM). The temporal spans of
the quasi-periodicities during different solar cycles are determined from the complex Morlet-wavelet analyses. The
Rieger quasi-periodicity (150–160 days) appeared during
cycle 21 and cycle 22. Each of the quasi-periodicities in the
studied range lies close to one or more planetary periodicities (orbital, or spring tidal, or heliocentric conjunction frequency). We discuss possible interpretations of our results,
and those of similar results obtained earlier by other authors,
towards understanding the mechanisms of excitation of various quasi-periodicities detected in solar variability parameters.
