Journal Article

Long-term evolution of cosmic ray modulation: a comprehensive analysis of solar and heliospheric influences (1964–2024)

Bouchachi, Dallel, Sedrati, Rafik

2025

Overview

This study provides a comprehensive analysis of galactic cosmic ray (GCR) modulation over six decades (1964–2024), covering Solar Cycles 20 through 25. Using an extensive data set of ground-based neutron monitor measurements, we examine the long-term evolution of GCR intensity about key solar and heliospheric parameters. The analysis includes an expanded set of variables, such as sunspot numbers as a proxy for solar activity, solar wind velocity, and interplanetary magnetic field strength. We apply advanced statistical methods, including the running cross-correlations method, phase-specific analyses (with and without time lag), and linear regression, to model the relationship between the dependent and independent variables. Our findings reveal clear modulation patterns across different solar cycles, emphasizing the significant impact of varying solar activities and interplanetary medium conditions on cosmic ray propagation. The study identifies notable temporal variations in cosmic ray transport mechanisms, particularly during the anomalous Solar Cycle 24 and the onset of Cycle 25. Statistical analysis shows that Pearson’s correlation between cosmic ray flux and sunspot numbers gradually decreased from Cycle 20 to Cycle 24, suggesting a weakening in solar modulation efficiency. Additionally, we detect a significant positive trend in the baseline CR intensity, increasing by approximately 0.1% per year, potentially linked to long-term changes in the heliospheric environment. The anomalously high cosmic ray flux during Solar Cycle 24’s minimum (2009–2010) is also examined in detail, revealing a unique combination of reduced solar magnetic field strength and altered heliospheric conditions. These results offer crucial insights into the long-term behavior of cosmic ray modulation and contribute to our understanding of space weather dynamics, which may inform future models for predicting cosmic ray flux variations.

• Publisher: IOP Publishing
• Subject: Cosmic ray propagation / Cosmic rays / Cross correlation / Field strength / Galactic cosmic rays / Heliosphere / heliospheric parameters / Independent variables / Interplanetary magnetic field / Interplanetary medium / long-term variability / Magnetic fields / Modulation / Solar activity / Solar cycle / solar cycle modulation / Solar magnetic field / Solar wind / Solar wind velocity / Statistical analysis / Statistical methods / Sunspot cycle / Sunspots / Time lag / Wind speed