Charge-sign dependent modulation of cosmic ray electrons and positrons up to extreme solar maximum conditions

Abstract

The charge-sign dependent modulation of cosmic rays is an important topic in solar modulation studies, providing insights into gradient, curvature, and current sheet drifts. Such studies, at higher levels of solar activity, have always been associated with challenges due to the limitations of numerical modulation models. We employ a three-dimensional numerical model based on stochastic differential equations and, owing to the numerical stability of this model, avoid such limitations at solar maximum conditions. We are therefore able to model results up to extreme solar maximum conditions, including the period of time over which the polarity reversal in the solar magnetic field takes place. We use our model to illustrate the effects of the tilt angle of the heliospheric current sheet that changes over the course of the solar activity cycle, and also discuss the effects when this is accompanied by a corresponding change in the magnitude of the heliospheric magnetic field. Given the results shown in this progress report, we expect our model to be able to reproduce recent data from AMS-02 and PAMELA, as well as provide us with useful predictions regarding the extent of drift effects during the next solar cycle.

A Perspective on the Solar Modulation of Cosmic Anti-Matter

“…The first robust observational evidence of charge-sign dependent solar modulation was reported in [138] and modelled in [139] using a drift model which, today, is known as a first generation drift model. These type of drift models predicted that during A > 0 polarity cycles the intensity ratio of negative to positively charged particles as a function of time should exhibit a ∧ shape profile while during A < 0 cycles it should exhibit a ∨ shape around minimum modulation periods, but when only the waviness of the HCS was changed with time [140]; for updates and new insights, see Figures 2 and 3 in [141]. It was found that when other modulation parameters were also changed with time in later generation drift models these distinctive shapes fade and are been smoothed out (e.g., [106]).…”