Propagation of Solar Energetic Particles in the Outer Heliosphere: Interplay between Scattering and Adiabatic Focusing

TL;DR

This study numerically investigates how scattering and adiabatic focusing influence solar energetic particle propagation in the outer heliosphere, revealing complex radial intensity patterns and explaining peculiar SEP phenomena.

Contribution

It introduces a detailed numerical analysis of the interplay between scattering and focusing effects on SEPs in the outer heliosphere, highlighting the limitations of simple radial intensity models.

Findings

Radial evolution of SEP intensities is complex and cannot be described by a single power law.

The interplay between scattering and focusing explains peculiar SEP phenomena in the outer heliosphere.

Radial dependence of SEP peak intensities varies with distance and is influenced by competing effects.

Abstract

The turbulence and spatial nonuniformity of the guide magnetic field cause two competitive effects, namely, the scattering effect and the adiabatic focusing effect, respectively. In this work, we numerically solve the five-dimensional Fokker-Planck transport equation to investigate the radial evolutions of these important effects undergone by the solar energetic particles (SEPs) propagating through interplanetary space. We analyze the interplay process between the scattering and adiabatic focusing effects in the context of three-dimensional propagation, with special attention to the scenario of the outer heliosphere, in which some peculiar SEP phenomena are found and explained. We also discuss the radial dependence of the SEP peak intensities from the inner through outer heliosphere, and conclude that it cannot be simply described by a single functional form such as R^{-\alpha} (R is radial distance), which is often used.