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, Lomnicky Stit and Huancayo/Haleakala) were analyzed by means of the wavelet transform method in the period range ~60 to ~1000 days. The contributions of the time evolution of three quasiperiodic cosmic ray signals (~150-d, ~1.3-y and ~1.7-y) to the global one are obtained. While the ~1.7-y quasiperiodicity, the most remarkable one in the studied interval, is strongly contributing to the cosmic ray intensity profile of solar cycle 21 (particularly in 1982), the ~1.3-y 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 quasiperiodicities are seen in the wavelet power spectra plots. Obtained results give a support to the claimed difference in the solar activity evolution during odd and even solar activity cycles.