“Long-term analysis of the diurnal variability of CRs observed on low cut-off rigidity neutron monitors”

Abstract

The diurnal variability of cosmic rays (CR) carries the signature of the modulation of galactic CR in the heliosphere, and in turn, it reflects the conditions prevailing in the heliosphere, which makes the study of daily variation of cosmic ray intensity important for the study of space weather and related features. In this study, the diurnal amplitude and phase of four neutron monitors with low cut-off rigidity have been studied by analyzing approximately five and a half solar cycles. This study covers the solar cycle (SC)-20 to SC-24/25, with a focus on the transition period between SC-24 and SC-25 in the context of diurnal isotropy with solar activity and polarity changes in the magnetic field of the Sun. Significant variations in the diurnal amplitude and phase of cosmic rays (CRs) are observed at low cut-off rigidity neutron monitors during both phases of solar activity in every solar cycle. The analysis also revealed significant relationships between diurnal variability and solar features. In all four neutron monitor datasets, there was a sharp and unmatched decline in amplitude and phase from 2018 to 2022 at the beginning of the 25th solar cycle. The next solar cycle is anticipated to be cooler than its predecessor and to exhibit a lower diurnal amplitude.