Heliospheric modulation and periodicities of galactic cosmic rays during 21-24 solar cycles

Galactic cosmic rays (GCRs) encounter an outward-moving solar wind with cyclic magnetic-field fluctuation and turbulence. This causes convection and diffusion in the heliosphere. The GCRs counts from the ground-based neutron monitor (NM) stations show intensity changes that are anti-correlated with the sunspot numbers with a lag of a few months. In this paper, we make a detailed correlative study between GCRs intensity at mid cut-off rigidity station (Lomnicky stit NM) and different solar/interplanetary parameters for cycles 21-24. We find a clear asymmetry in the cross-correlation between GCRs and solar/heliospheric activity indicators for both odd and even-numbered solar cycles. The time-lags between GCRs and solar/heliospheric parameters are found different in different solar cycles as well as in the opposite polarity states (A < 0 and A > 0) within the same solar cycle. Further, we have studied the mid-term periodicities of GCRs and found the presence of well - known Rieger type and quasi-biennial oscillations (QBOs) in the power spectrum. Possible explanations of the observed results are discussed in light of 3 D modulation models, including drift effect.