---
abstract: 'Multi-spacecraft observations of widespread solar energetic particle (SEP)
  events indicate that perpendicular (to the mean field) diffusion is an important
  SEP transport mechanism. However, this is in direct contrast to so-called spike
  and drop-out events, which indicate very little lateral transport. To better understand
  these seemingly incongruous observations, we discuss the recent progress made towards
  understanding and implementing perpendicular diffusion in transport models of SEP
  electrons. This includes a re-derivation of the relevant focused transport equation,
  a discussion surrounding the correct form of the pitch-angle dependent perpendicular
  diffusion coefficient and what turbulence quantities are needed as input, and how
  models lead to degenerate solutions of the particle intensity. Lastly, we evaluate
  the validity of a diffusion approach to SEP transport and conclude that it is valid
  when examining a large number of (an ensemble of) events, but that individual SEP
  events may exhibit coherent structures related to the magnetic field turbulence
  at short timescales that cannot be accounted for in this modelling approach.'
adsnote: Provided by the SAO/NASA Astrophysics Data System
adsurl: https://ui.adsabs.harvard.edu/abs/2020JPhCS1620a2021S
authors:
- R. D. Strauss
- J. P. van den Berg
- P. J. Steyn
- F. J. Effenberger
- N. Wijsen
- T. Laitinen
- J. A. le Roux
booktitle: Journal of Physics Conference Series
category: publications
date: '2020-09-01'
doi: 10.1088/1742-6596/1620/1/012021
draft: false
eid: '012021'
featured: false
month: September
pages: '012021'
projects: []
publication: Journal of Physics Conference Series
publication_types:
- '2'
series: Journal of Physics Conference Series
tags: []
title: 'Perpendicular diffusion of solar energetic particles: When is the diffusion
  approximation valid?'
type: INPROCEEDINGS
volume: '1620'
year: '2020'
---