# Numerical modeling of cosmic-ray transport in the heliosphere and interpretation of the proton-to-helium ratio in Solar Cycle 24

## TL;DR

This paper develops a numerical model to understand cosmic-ray transport in the heliosphere, explaining the observed proton-to-helium ratio variations during Solar Cycle 24 through diffusion properties.

## Contribution

It introduces a detailed numerical model linking cosmic-ray diffusion characteristics to the temporal evolution of the proton-to-helium ratio, incorporating analytical solutions.

## Key findings

- Long-term proton-to-helium ratio behavior explained by diffusion dependence.
- Model successfully reproduces observed temporal variations.
- Highlights importance of mass/charge dependent diffusion in CR transport.

## Abstract

Thanks to space-borne experiments of cosmic-ray (CR) detection, such as the AMS and PAMELA missions in low-Earth orbit, or the Voyager-1 spacecraft in the interstellar space, a large collection of multi-channel and time-resolved CR data has become available. Recently, the AMS experiment has released new precision data, on the proton and helium fluxes in CRs, measured on monthly basis during its first six years of mission. The AMS data reveal a remarkable long-term behavior in the temporal evolution of the proton-to-helium ratio at rigidity $R = p/Z <$ 3 GV. As we have argued in a recent work, such a behavior may reflect the transport properties of low-rigidity CRs in the inteplanetary space. In particular, it can be caused by mass/charge dependence of the CR diffusion coefficient. In this paper, we present our developments in the numerical modeling of CR transport in the Milky Way and in the heliosphere. Within our model, and with the help of approximated analytical solutions, we describe in details the relations between the properties of CR diffusion and the time-dependent evolution of the proton-to-helium ratio.