Modulation of Galactic Cosmic Rays in the Inner Heliosphere over Solar Cycles

TL;DR

This paper presents a numerical model that successfully reproduces the 11-year and 22-year modulation cycles of galactic cosmic rays in the inner heliosphere, incorporating magnetic field and turbulence variations over solar cycles.

Contribution

The study introduces a comprehensive numerical model that accounts for magnetic field modifications, turbulence, and solar magnetic polarity changes to simulate GCR modulation over solar cycles.

Findings

Model reproduces observed GCR modulation cycles.

Good agreement with multiple spacecraft observations.

Highlights the role of magnetic turbulence in GCR modulation.

Abstract

The 11-year and 22-year modulation of galactic cosmic rays (GCRs) in the inner heliosphere are studied using a numerical model developed by Qin and Shen in 2017. Based on the numerical solutions of Parker's transport equations, the model incorporates a modified Parker heliospheric magnetic field, a locally static time delayed heliosphere, and a time-dependent diffusion coefficients model in which an analytical expression of the variation of magnetic turbulence magnitude throughout the inner heliosphere is applied. Furthermore, during solar maximum, the solar magnetic polarity is determined randomly with the possibility of $A>0$ decided by the percentage of the north solar polar magnetic field being outward and the south solar polar magnetic field being inward. The computed results are compared with several GCR observations, e.g., IMP 8, SOHO/EPHIN, Ulysses, Voyager 1 \& 2, at various energies and show good agreement. It is shown that our model has successfully reproduced the 11-year and 22-year modulation cycles.