Unfolding Drift Effects for Cosmic Rays over the Period of the Sun’s Magnetic Field Reversal

Abstract

A well-established, comprehensive 3D numerical modulation model is applied to simulate galactic protons, electrons, and positrons from 2011 May to 2015 May, including the solar magnetic polarity reversal of Solar Cycle 24. The objective is to evaluate how simulations compare with corresponding Alpha Magnetic Spectrometer observations for 1.0–3.0 GV and what underlying physics follows from this comparison to improve our understanding of how the major physical modulation processes change, especially particle drift, from a negative to a positive magnetic polarity cycle. Apart from their local interstellar spectra, electrons and positrons differ only in their drift patterns, but they differ with protons in other ways such as adiabatic energy changes at lower rigidity. In order to complete the simulations for oppositely charged particles, antiproton modeling results are also obtained. Together, observations and corresponding modeling indicate the difference in the drift pattern before and after the recent polarity reversal and clarify to a large extent the phenomenon of charge-sign dependence during this period. The effect of global particle drift became negligible during this period of no well-defined magnetic polarity. The resulting low values of particles’ mean free paths (MFPs) during the polarity reversal contrast their large values during solar minimum activity and as such expose the relative contributions and effects of the different modulation processes from solar minimum to maximum activity. We find that the drift scale starts recovering just after the polarity reversal, but the MFPs keep decreasing or remain unchanged for some time after the polarity reversal.

Galactic Cosmic Ray Intensity in Periods of the Heliospheric Magnetic Field Inversion

“…4 the calculated proton spectra with three variants of drift velocity (multiplied by 1 (dotted), -1 (dash-dotted), 0 (dashed)) are shown for three every other rotations in panel (d). The relative position of three lines shows that the particles feel the change of the HMF polarity in 1 or 2 CRs and the HMF inversion is really very fast which contradicts to [4].…”

A Numerical Study of the Effects of a Corotating Interaction Region on Cosmic-Ray Transport. II. Features of Cosmic-Ray Composition and Rigidity

“…. The essence of this latter process is that particle drift is not reduced at higher rigidity (see Figure 8 by Potgieter et al 2014 and Figure 11 by Aslam et al 2023). In the SDE model, the 6) and (7) for GCR protons (upper left panel), He-4 (upper right panel), and He-3 (lower panel).…”

“…, which means that the reduction is applied only at lower rigidity, as is usually done in global modulation studies (e.g., Ngobeni et al 2022;Aslam et al 2021Aslam et al , 2023. These reductions are all indicated in the figure legend.…”

Modulation of Cosmic-Ray Antiprotons in the Heliosphere: Simulations for a Solar Cycle

“…Combining the AMS and PAMELA proton spectra over the period 2006 July-2019 November provides us with more than 13 yr of proton spectra as the basis for our observational motivated and data-driven simulations. See also the simulations of proton, antiproton, electron, and positron spectra by Aslam et al (2023).…”

“…Aslam et al (2019),Corti et al (2019),Ngobeni et al (2020),Aslam et al (2021),Ngobeni et al (2022), andAslam et al (2023).…”