Numerical modeling of cosmic rays in the heliosphere: Analysis of proton data from AMS-02 and PAMELA

Abstract

Galactic cosmic rays (CRs) inside the heliosphere are affected by solar modulation. To investigate this phenomenon and its underlying physical mechanisms, we have performed a data-driven analysis of the temporal dependence of the CR proton flux over the solar cycle. We have modeled the solar modulation effect by means of stochastic simulations of cosmic particles in the heliospheric plasma. We have constrained our model using the recent time-resolved measurements of CR proton fluxes reported by AMS-02 and PAMELA experiments, on monthly basis, from mid-2006 to mid-2017. With a global statistical analysis, we have determined the key model parameters that rules the CR transport, its dependence on the particle rigidity, and its evolution over the solar cycle. Our data sample comprises epochs of solar minimum, solar maximum, as well as epochs with magnetic reversal and opposite polarities. Along with the evolution of the CR transport parameters, we study their relationship with solar activity proxies and interplanetary parameters. We find that the rigidity dependence of the parallel mean free path of CR diffusion shows a remarkable time dependence, indicating a long-term variability in the interplanetary turbulence that interchanges across different regimes over the solar cycle. The evolution of CR diffusion parameters show a delayed correlation with the sunspot number, reflecting the dynamics of the heliospheric plasma, and different dependencies for opposite states of magnetic polarity, reflecting the influence of charge-sign dependent drift in the CR modulation.

Data driven analysis of Galactic cosmic rays in the heliosphere: diffusion of cosmic protons and nuclei

“…In this work, the equation is solved using the stochastic differential equation (SDE) method in steady-state conditions (𝜕/𝜕𝑡 = 0) [8], based on a customized version of the Solarprop framework [9,10]. We implemented a 2D model of heliosphere described by radius 𝑟 and heliolatitude 𝜃 [11]. The heliosphere is modeled as a spherical cavity centered to the Sun from which the wind flows radially.…”

“…For a given epochs 𝑡, the average is calculated within a time window [𝑡 − Δ𝑇, 𝑡], with Δ𝑇 = 6 − 12 months. The window is chosen so that the BMA values of α (from WSO) and B0 (from ACE) reflect the average HMF conditions sampled by GCRs arriving Earth [11,25]. The remaining diffusion parameters 𝐾 0 , 𝑎, and 𝑏 have been determined with a global fit on the GCR proton measurements from AMS-02 and PAMELA.…”

New insights from cross-correlation studies between Solar activity and Cosmic-ray fluxes

“…In this respect, a big challenge is to establish reliable relations between the GCR modulation effect and the Sun's variability. Several physical models have been developed in order to predict the evolution of the GCR intensity in the inner heliosphere [4][5][6][7][8]. Investigating solar modulation and its underlying physical mechanisms is central in astrophysics.…”

Spatial and Temporal Variations of the Chandra ACIS Particle-Induced Background and Development of a Spectral-Model Generation Tool

“…Such a spectral variation is assumed to be due to the cosmic-ray spectral modulation in accordance with solar activity (e.g., Mizuno et al 2004;Fiandrini et al 2020), so that this is assumed to depend on a total particle-induced background rate. The spectrum becomes harder in higher solar-activity periods, and this tendency is consistent with the cosmic-ray spectral modulation (e.g., Mizuno et al 2004;Fiandrini et al 2020). Applying this model, we fit all the ACIS-stowed observation spectra simultaneously to determine the best-fit R 0 and α values for each CCD and each observation mode.…”