Multi-spacecraft constraints on relativistic solar energetic particle transport in the widespread 28 October 2021 event

Abstract

Aims. We investigated the transport of solar energetic particles (SEPs) during the relativistic widespread event of 28 October 2021, quantifying the role of parallel and perpendicular diffusion and constraining the spatial extent of the injection region. Methods. We employed inverse modeling of particle focused transport and 2D numerical simulations including cross-field diffusion. Multi-spacecraft observations from STEREO-A, Solar Orbiter, and near-Earth spacecraft are used to reproduce particle intensity profiles and anisotropies across a wide range of electron and proton energies. Simulated flux profiles are compared across different heliolongitudes to derive consistent transport parameters. Results. The analysis yields parallel mean free paths within or slightly above the Palmer consensus range, and perpendicular mean free paths that correspond to $\sim 1$--$3\%$ of parallel for electrons and $\sim 5$--$10\%$ for protons. The injection region is found to be relatively narrow ($\le 20^{\circ }$), and decreasing with particle rigidity. Multipoint simulations indicate that the observed flux and anisotropy profiles can only be reproduced by a narrow injection region and significant cross-field diffusion. Electron and proton release times align well with the parent X1.0 flare and associated coronal mass injection (CME) onset, indicating that a compact acceleration region coupled with efficient interplanetary diffusion governed the event's broad spatial extent.

References in corpus (18)

• The Solar Orbiter mission -- Science overview
• Acceleration and propagation of Solar Energetic Particles
• Solar-MACH: An open-source tool to analyze solar magnetic connection configurations
• Solar Energetic Particles (Second Edition)
• Solar energetic particle access to distant longitudes through turbulent field-line meandering
• On Aspects Pertaining to the Perpendicular Diffusion of Solar Energetic Particles
• Perpendicular Diffusion of Solar Energetic Particles: Model Results and Implications for Electrons
• The First Ground Level Enhancement of Solar Cycle 25 on 28 October 2021
• The 17 April 2021 widespread solar energetic particle event
• From Sun to interplanetary space: What is the pathlength of Solar Energetic Particles?
• A Primer on Focused Solar Energetic Particle Transport: Basic physics and recent modelling results
• Modelling Solar Energetic Particle transport near a wavy Heliospheric Current Sheet
• 3D propagation of relativistic solar protons through interplanetary space
• Solar Energetic Particle Time Series Analysis with Python
• The multi-spacecraft high-energy solar particle event of 28 October 2021
• On the reason for the widespread energetic storm particle event of 13 March 2023
• On the onset delays of solar energetic electrons and protons: Evidence for a common accelerator
• The evolution of coronal shock wave properties and their relation with solar energetic particles