Radial Evolution of ICME-Associated Particle Acceleration Observed by Solar Orbiter and ACE

TL;DR

This study analyzes how particle acceleration at an ICME shock evolves radially from 0.45 au to 1 au, revealing differences in spectral shapes influenced by shock geometry and propagation effects, based on Solar Orbiter and ACE data.

Contribution

It provides the first detailed comparison of ion spectra at different radial distances during an ICME event, highlighting the impact of shock geometry and suprathermal ion populations.

Findings

Spectral shapes differ significantly between 0.45 and 1 au.

Higher energy fluxes at 1 au are influenced by suprathermal He+ ions.

Shock geometry affects the presence of spectral breaks.

Abstract

On 2022 March 10, a coronal mass ejection (CME) erupted from the Sun, resulting in Solar Orbiter observations at 0.45 au of both dispersive solar energetic particles arriving prior to the interplanetary CME (ICME) and locally accelerated particles near the ICME-associated shock structure as it passed the spacecraft on 2022 March 11. This shock was later detected on 2022 March 14 by the Advanced Composition Explorer (ACE), which was radially aligned with Solar Orbiter, at 1 au. Ion composition data from both spacecraft -- via the Solar Orbiter Energetic Particle Detector/ Suprathermal Ion Spectrograph (EPD/SIS) and the Ultra Low Energy Isotope Spectrometer (ULEIS) on ACE -- allows for in-depth analysis of the radial evolution of species-dependent ICME shock-associated acceleration processes for this event. We present a study of the ion spectra observed at 0.45 and 1 au during both the gradual solar energetic particle (SEP) and energetic storm particle (ESP) phases of the event. We find that the shapes of the spectra seen at each spacecraft have significant differences that were likely caused by varying shock geometry: Solar Orbiter spectra tend to lack spectral breaks, and the higher energy portions of the ACE spectra have comparable average flux to the Solar Orbiter spectra. Through an analysis of rigidity effects on the spectral breaks observed by ACE, we conclude that the 1 au observations were largely influenced by a suprathermal pool of $\mathrm{He}^{+}$ ions that were enhanced due to propagation along a stream interaction region (SIR) that was interacting with the ICME at times of observation.