Time evolution of low-frequency periodicities in cosmic ray intensity

The long-time series of daily means of cosmic-ray intensity observed by
four neutron monitors at different cutoff rigidities (Calgary, Climax,
Lomnický Štít and Huancayo/Haleakala) were analyzed by means of the
wavelet transform method in the period range about 60 to about 1000 days.
The contributions of the time evolution of three quasi-periodic cosmic-ray
signals (about 150 d, about 1.3 yr and about 1.7 yr) to the global one are
obtained. While the about 1.7-yr quasi-periodicity, the most remarkable
one in the studied interval, strongly contributes to the cosmic ray
intensity profile of solar cycle 21 (particularly in 1982), the about 1.3-
yr one, which is better correlated with the same periodicity of the
interplanetary magnetic field strength, is present as a characteristic
feature for the decreasing phases of the cycles 20 and 22. Transitions
between these quasi-periodicities are seen in the wavelet power spectra
plots. Obtained results support the claimed difference in the solar
activity evolution during odd and even solar activity cycles.