Quasi-periodicities in cosmic rays recorded by the KACST muon detector during 2002–2012

Abstract In this study, daily cosmic ray data obtained with the KACST muon detector for the period 2002–2012 were analyzed for quasi-periodicities. Power-spectrum analysis was carried out and several periodicities were identified. The results reveal several periodicities at different frequency scales: 817 days (∼2.19 years), 617 days (∼1.7 years), 475 days (∼1.3 years), 421 days (1.15 years), 290 days (∼0.8 years), 227 days (∼0.62 years), 185 days (∼0.52 years), 153 days, 135 days, 120 days, 93 days, 84 days, 73 days, 65 days, 53-45 days, 38 days, 31 days, 25-27 days, 21 days and 13 days. The obtained periodicities are in an agreement with those previously reported by several investigators. The identified periodicities have strong relevance to solar activity parameters such as variations in the interplanetary magnetic field. In comparison, the data from two neutron monitors (NMs), Lomnický stit and Oulu NMs, for the same period were used and their power spectra were correspondingly obtained. Similarities and differences in the position of the cosmic-ray peaks measured by the KACST muon detector and by the two NMs have been presented and discussed. While most of the periodicities reported by the muon detector are also found in the NM data, the ∼1.7-yr variation is not found. Instead, a shift of 1.6 – 1.8 years in the NM data is observed which may be due to the limited epoch considered in this study.