A study of the heliospheric modulation of cosmic rays in the past solar cycles

Cosmic rays are high-energy particles originating from outside the solar system, and their flux is modulated by the heliosphere, the region of space influenced by the sun. This study investigates the heliospheric modulation of cosmic rays over five consecutive solar cycles (20-24), spanning from 1964 to 2019, focusing on the variations in cosmic ray intensity with solar activity. A long-term correlative study has been done using the values of the monthly mean of sunspot number (SSN) and cosmic ray data from ground-based Neutron Monitor Stations (Kiel, Moscow and Oulu). By analysing the cosmic ray intensity during these cycles, a significant variation in the cosmic ray flux and its modulation by the heliosphere is shown. The statistical analysis of the data depicts a very high anti-correlation association between solar activity and cosmic rays’ intensity for the period studied; which is consistent with earlier findings. The results in this study demonstrate distinct differences in the cosmic ray intensity between solar cycles and the level of statistical association between sunspot number and cosmic rays varies from cycle to cycle. Solar cycle 21 was observed to have a slightly weaker anti-correlation value as compared to other cycles; this displays a solar cycle-dependent modulation effect necessitating further research. The cut-off rigidity, which ranges from 0.80 to 8.28 GV, and the influence of cut-off rigidity on the energy spectrum of the cosmic ray was observed as the station with the lowest cut-off rigidity generated the strongest anti-correlation value. This research provides new insights into the long-term variability of cosmic rays and the heliospheric modulation processes, with important applications in space weather and radiation protection.