Constraining the Charge-, Time- and Rigidity-Dependence of Cosmic-Ray Solar Modulation with AMS-02 Observations during Solar Cycle 24

TL;DR

This study uses AMS-02 data and solar wind measurements to analyze how solar modulation affects cosmic-ray spectra based on charge, time, and rigidity during solar cycle 24, revealing complex magnetic field influences.

Contribution

It introduces an analytical model that captures the charge-, time-, and rigidity-dependent solar modulation of cosmic rays, validated with recent AMS-02 observations.

Findings

Evidence for charge- and rigidity-dependence of solar modulation during cycle 24

The model explains the large-scale time evolution of positive cosmic-ray fluxes from 1 to 10 GV

Electron fluxes are more complex due to magnetic field variability

Abstract

Our basic theoretical understanding of the sources of cosmic rays and their propagation through the interstellar medium is hindered by the Sun, that through the solar wind affects the observed cosmic-ray spectra. This effect is known as solar modulation. Recently released cosmic-ray observations from the Alpha Magnetic Spectrometer (AMS-02) and publicly available measurements of the solar wind properties from the Advanced Composition Explorer and the Wilcox observatory allow us to test the analytical modeling of the time-, charge- and rigidity-dependence of solar modulation. We rely on associating measurements on the local heliospheric magnetic field and the heliospheric current sheet's tilt angle, to model the time-dependence and amplitude of cosmic-ray solar modulation. We find evidence for the solar modulation's charge- and rigidity-dependence during the era of solar cycle 24. Our analytic prescription to model solar modulation can explain well the large-scale time-evolution of positively charged cosmic-ray fluxes in the range of rigidities from 1 to 10 GV. We also find that cosmic-ray electron fluxes measured during the first years of cycle 24 are less trivial to explain, due to the complex and rapidly evolving structure of the Heliosphere's magnetic field that they experienced as they propagated inwards.