Neutron monitor counting rates measurements from 1964 to 2019 corresponding with the Solar Cycles 20-24 have been analyzed in this work.
In this work, Global Neutron Monitor (GNM) is constructed over the last five Solar Cycles and is considered as a virtual representative station to characterize solar activity. Morlet wavelet analysis was applied to the GNM in order to determine periodicities.
The 27-day period and its second subharmonic (13-day period), related to solar synodic rotation, a periodicity between 45 and 84 days, the Rieger period (~151 days) and nearly annual period have been detected in all SCs in both analyzed magnitudes. On a larger scales, 1.3-, 1.7–,11– and 22–year periods were obtained in GNM counting rates.
A temporal evolution of the periodicities obtained has been studied.
It is suggested that the same phenomenon produces the periodicities since their peaks are at similar times. This physical phenomenon could be a modulation effect related to solar rotation. We suggest the magnetic Rossby waves produce indirectly these periodicities in neutron monitor counting rates.