Quasi-periodicities in cosmic rays and time lag with the solar activity at a middle latitude neutron monitor: 1982-2017

摘要

Galactic cosmic rays (GCRs) after entering the heliosphere are continuously modulated by the change in solar wind and the associated heliosphericmagnetic field. GCRs also follow about 11 year sunspot cycle in an inverse way with some time lag of few months to years, which usually varies from cycle to cycle Badruddin etal. 2007; Kane 2014; Aslam and Badruddin 2015 (e.g. Badruddin et al. in Astron. Astrophys. 466(2):697-704, 2007; Kane in Sol. Phys. 289:2669-2675, 2014; Aslam and Badruddin in Sol. Phys. 290:2333, 2015). In this work, we have investigated solar modulation of GCRs measured at three mid cut-off rigidity neutron monitor stations for the period of 1982 to 2017, covering two complete solar cycles and a major part of the recent cycle24. We study the time lag between GCRs intensity and various solar, geomagnetic and interplanetary parameters separately during the solar cycles under investigation. Further, we have investigated the presence and temporal evolution of mid term quasi-periodicities of GCRs time series during the above mentioned phases utilizing both Morlet wavelet transform and Scargle periodogram technique. Power spectral analysis indicates the presence of several mid term quasi-periodicities including Rieger type and Quasi-biennial oscillations. We discuss the findings and compare them with results of other authors.