Abstract
We have studied long-term variations of galactic cosmic-ray (GCR) intensity in relation to the sunspot number (SSN) during the most recent solar cycles. This study analyses the time lag between the GCR intensity and SSN, and hysteresis plots of the GCR count rate against SSN for Solar Cycles 20 – 23, to validate a methodology against previous results in the literature, before applying the method to provide a timely update on the behaviour of Cycle 24. Plots of SSN versus GCR show a clear difference between the odd- and even-numbered cycles. Linear and elliptical models have been fit to the data, with the linear fit and elliptical model proving the more suitable model for even- and odd-numbered solar-activity cycles, respectively, in agreement with previous literature. Through the application of these methods for Solar Cycle 24, it has been shown that Cycle 24 experienced a lag of two to four months between the GCR intensity and SSN, and this follows the trend of the preceding activity cycles, albeit with a slightly longer lag than previous even-numbered cycles. It has been shown through the hysteresis analysis that the linear fit is a better representative model for Cycle 24, as the ellipse model does not show a significant improvement, which is also in agreement with previous even-numbered cycles.
Highlights
Galactic cosmic rays (GCRs) are charged particles and atomic nuclei with energies spanning the range from a few MeV up to approximately 1021 eV, which encroach upon the Earth from B E
The hysteresis loops between yearly averaged sunspot number (SSN) and GCR intensity for each station were first modelled with a linear regression for both odd and even solar-activity cycles, and the odd cycles were separately re-modelled by ellipse fitting to show that this provides a more representative fit, as suggested by Inceoglu et al (2014)
As CRs are modulated by the heliosphere during the 11-year solar activity cycle, and this effect has been studied for previous solar cycles, the principal aim of this study was to investigate the nature of GCRs during the current activity of Cycle 24 as it draws to a minimum
Summary
Galactic cosmic rays (GCRs) are charged particles and atomic nuclei with energies spanning the range from a few MeV up to approximately 1021 eV, which encroach upon the Earth from B E. Chaplin all directions (Giacalone, 2010) They mainly originate outside the solar system, within the Milky Way; they are expected to originate from other galaxies (Aab et al, 2017). GCRs at the top of the atmosphere are mostly composed of protons (≈ 87%) and α-particles (≈ 12%), with a smaller contribution (≈ 1%) from heavier nuclei (Dunai, 2010)
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