The transport of galactic cosmic rays in heliosphere: The HELMOD model compared with other commonly employed solar modulation models

HELMOD model allows one to describe how solar modulation affects the propagation of galactic cosmic rays (GCRs) through the helio-sphere by solving the Parker transport equation. HELMOD provides modulated spectra for protons and nuclei during high and low solar activity periods, in the inner and outer heliosphere, at Earth location and outside the ecliptic plane, as well as at different distances from Sun in the inner and outer heliosphere. The GCRs mainly constitute the high-energy population of the so-called space radiation envi-ronment. Modulated cosmic-ray spectra of protons and nuclei, obtained from HELMOD and other solar modulation codes were compared to the AMS-02 spectra ranging from GeV up to TeV energies. Concerning other commonly used solar modulation models, HELMOD mod-ulated spectra are available over the entire rigidity range and observation period of AMS-02 mission. A quantitative comparison among models was carried out using AO, i.e., the relative difference between the experimental and simulated fluences, and gRMS, i.e., the error -weighted root mean square of the relative difference between AMS-02 experimental data and simulated differential intensities. HELMOD was found to achieve a good agreement over the full set of experimental data with, typically, AO within +/- 2:5% and gRMSwithin 5%. Usu-ally larger or, in a few cases, much larger values for AO and gRMSwere found for the other models. (c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

Automated summary

The HELMOD model allows for the description of how solar modulation affects the propagation of galactic cosmic rays in the heliosphere. It provides modulated spectra for different periods and locations, and achieves good agreement with experimental data compared to other models.