Time and Charge-Sign Dependence of the Heliospheric Modulation of Cosmic Rays

TL;DR

This study models the heliospheric modulation of cosmic-ray electrons and positrons over a solar cycle, revealing how charge-sign dependent processes and particle drifts influence observed spectra during different solar activity phases.

Contribution

It introduces a comprehensive 3D modulation model that accurately reproduces observed positron/electron ratios from 2006 to 2015, highlighting the role of particle drifts and solar magnetic polarity reversal.

Findings

Reproduced observed positron/electron ratios with qualitative and quantitative accuracy.

Quantified the impact of particle drifts on charge-sign dependent modulation.

Demonstrated the evolution of modulation processes during solar activity phases.

Abstract

Simultaneous and continuous observations of galactic cosmic-ray electrons and positrons from the PAMELA and AMS02 space experiments are most suitable for numerical modeling studies of the heliospheric modulation of these particles below 50 GeV. A well-established comprehensive three-dimensional modulation model is applied to compute full spectra for electrons and positrons with the purpose of reproducing the observed ratio positrons/electrons for a period which covers the previous long and unusual deep solar minimum activity and the recent maximum activity phase including the polarity reversal of the solar magnetic field. For this purpose the very local interstellar spectra for these particles were established first. Our study is focused on how the main modulation processes, including particle drifts, and other parameters such as the three major diffusion coefficients, had evolved, and how the corresponding charge-sign dependent modulation had occurred subsequently. The end result of our effort is the detailed reproduction of positron/electrons from 2006 to 2015, displaying both qualitative and quantitative agreement with the main observed features. Particularly, we determine how much particle drifts is needed to explain the time dependence exhibited by the observed positron/electron during each solar activity phase, especially during the polarity reversal phase when no well-defined magnetic polarity was found.