Behaviour of 27-Day and 13.5-Day Periodicities in Galactic Cosmic Particles as Observed by Spacecraft and Neutron Monitors During Different Solar Polarity Cycles

Abstract

An analysis has been made of the behaviour of the 27-day and 13.5-day periodicities in proton, C, and O galactic-cosmic-ray (GCR) particles at different energies as observed by the Advanced Composition Explorer (ACE) and SOHO (Solar and Heliospheric Observatory) spacecraft during both Solar Cycles 23 and 24. In addition, the behaviour of the 27-day and 13.5-day periods in the solar-wind-modulation parameter zeta = BIMF × VSW has been investigated during the same time interval to determine the existence of a possible solar-polarity dependence. Ground-based neutron-monitor (NM) observations, corresponding to different rigidity cutoff [RC] parameters, were also studied to determine the temporal behaviour of both the 27-day and 13.5-day periods during Cycles 23 and 24, revealing a statistically significant solar-polarity correlation. The Lomb–Scargle periodogram technique has been employed to extract spectral information from the above-mentioned observations for each individual year from 2001 – 2009 (Cycle 23) and 2010 – 2019 (Cycle 24). Daily mean energetic ACE and SOHO particle measurements are used to identify how both the 27-day and 13.5-day periodicities vary during each individual year during these cycles as a function of particle mean energy. This spectral analysis of proton, C, and O galactic-cosmic-particle data at different energies revealed that both the 27-day and 13.5-day periods are stronger during the minimum of Solar Cycle 24/25 when A > 0 (solar dipole pointing North) in comparison to the minimum of Cycle 23/24 when A < 0 (solar dipole pointing South) at certain energy levels. This showed a particularly strong energy-dependent behaviour for both periodicities. This article reports for the first time an annual time- and energy-dependent behaviour of both the 27-day and 13.5-day periodicities in daily-mean galactic cosmic particles observed by spacecraft and ground-based neutron monitors during consecutive Solar Cycles 23 and 24, corresponding to opposite solar-magnetic-field orientations. Periodicity behaviour in heliospheric solar-wind data corroborate these results in general.