Spectral Analysis of Rieger Periodicity Behaviour in O and Fe Galactic Cosmic Particles Observed by ACE in Solar Cycles 23 and 24

The behaviour of the Rieger periodicity at 152 – 156 days in O and Fe galactic cosmic ray (GCR) particles, at different energies as observed by the Advanced Composition Explorer (ACE) satellite, has been studied. Energetic particle data between 2000 and 2019 have been analysed using the Lomb-Scargle periodogram and Morlet wavelet spectral analysis techniques. Daily mean energetic particle measurements are used to identify how the Rieger periodicity varies in each individual year as a function of the mean particle energy. In particular, spectral analysis of galactic cosmic particle data at different energies revealed that the Rieger period occurs exceptionally strong during Solar Cycle 23 when A < 0 (solar dipole pointing south) compared to Cycle 24 when A > 0 (solar dipole pointing north). This article reports for the first time the time-dependence of the Rieger (152 – 156 days) periodicity in O and Fe GCR particles at various energies ranging from ≈ 70 MeV/n to ≈ 471 MeV/n.