Perpendicular Diffusion in the Transport of Solar Energetic Particles from Unconnected Sources: The Counter-streaming Particle Beams Revisited

TL;DR

This paper investigates the mechanisms behind counter-streaming solar energetic particle beams, focusing on the roles of magnetic reflection and perpendicular diffusion, to better understand particle transport in interplanetary space.

Contribution

The study revisits the phenomenon of counter-streaming SEP beams, clarifies previous results, and discusses the roles of magnetic reflection and perpendicular diffusion in their formation.

Findings

Perpendicular diffusion influences SEP beam formation.

Magnetic reflection may contribute to counter-streaming features.

Clarification of previous interpretations of SEP observations.

Abstract

In some solar energetic particle (SEP) events, a counter-streaming particle beam with a deep depression of flux near 90 degrees pitch angle during the beginning phase is observed. Two different interpretations exist in the community to explain this interesting phenomenon. One explanation invokes the hypothesis of an outer reflecting boundary or a magnetic mirror beyond the observer. The other one considers the effect of the perpendicular diffusion on the transport process of SEPs in the interplanetary space. In this work, we revisit the problem of the counter-streaming particle beams observed in SEP events and discuss the possible mechanisms responsible for the formation of this phenomenon. We clarify some results in previous works.