Delayed maximum energy solar energetic particle events: Statistical analysis from Solar Orbiter
Abstract
Investigations of solar energetic particles (SEPs) have long utilized the dispersive nature of onset times, as in, the earlier arrival of higher-energy particles compared to lower-energy particles, to infer information such as the path length to the acceleration site at the time of initial particle release. However, recent observations by Solar Orbiter and Parker Solar Probe have begun to characterize SEP events with an apparent delay in arrival times of the higher energy portion of the particle distribution, above a critical energy separating the delayed particles from that of the typical velocity dispersion signature at lower energies. Features of these delayed maximum energy (DME) SEP events, sometimes referred to as "inverse velocity dispersion" events, could provide new insight into the impacts of magnetic connectivity to locations along an expanding coronal mass ejection-driven (CME-driven) shock wave, variations of acceleration along the shock surface, and transport effects in the inner heliosphere. This study focuses on the occurrence rate and characteristics of DME events observed by Solar Orbiter relative to their footpoint locations with respect to the initial flare site. These DME events show a bias in occurrence rate towards events when the observer's footpoints were westward of the associated flare location. Additionally, estimated locations at which the highest-energy particles of DME events are released into the flux tube suggest continued release of increasingly higher-energy particles from the CME-driven shock into the connected flux tube well into the inner heliosphere. This indicates that DME events could be attributed to inner heliospheric effects and are not actually coronal in origin. This finding is consistent with previous observations and interpretations of SEP events connected westward of the associated flare.
Versions
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BibTeX
@misc{allen2026delayed,
title = {{Delayed maximum energy solar energetic particle events: Statistical analysis from Solar Orbiter}},
author = {R. C. Allen and G. C. Ho and G. M. Mason and Z. Ding and M. H. Walker and A. Kouloumvakos and R. F. Wimmer-Schweingruber and J. Rodriguez-Pacheco and S. K. Vines and R. J. Filwett and Z. Xu and C. M. S. Cohen},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.35520},
eprint = {2610.35520},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.35520},
}
RIS
TY - UNPB
TI - Delayed maximum energy solar energetic particle events: Statistical analysis from Solar Orbiter
AU - R. C. Allen
AU - G. C. Ho
AU - G. M. Mason
AU - Z. Ding
AU - M. H. Walker
AU - A. Kouloumvakos
AU - R. F. Wimmer-Schweingruber
AU - J. Rodriguez-Pacheco
AU - S. K. Vines
AU - R. J. Filwett
AU - Z. Xu
AU - C. M. S. Cohen
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.35520
UR - https://arxiv.org/abs/2610.35520
AB - Investigations of solar energetic particles (SEPs) have long utilized the dispersive nature of onset times, as in, the earlier arrival of higher-energy particles compared to lower-energy particles, to infer information such as the path length to the acceleration site at the time of initial particle release. However, recent observations by Solar Orbiter and Parker Solar Probe have begun to characterize SEP events with an apparent delay in arrival times of the higher energy portion of the particle distribution, above a critical energy separating the delayed particles from that of the typical velocity dispersion signature at lower energies. Features of these delayed maximum energy (DME) SEP events, sometimes referred to as "inverse velocity dispersion" events, could provide new insight into the impacts of magnetic connectivity to locations along an expanding coronal mass ejection-driven (CME-driven) shock wave, variations of acceleration along the shock surface, and transport effects in the inner heliosphere. This study focuses on the occurrence rate and characteristics of DME events observed by Solar Orbiter relative to their footpoint locations with respect to the initial flare site. These DME events show a bias in occurrence rate towards events when the observer's footpoints were westward of the associated flare location. Additionally, estimated locations at which the highest-energy particles of DME events are released into the flux tube suggest continued release of increasingly higher-energy particles from the CME-driven shock into the connected flux tube well into the inner heliosphere. This indicates that DME events could be attributed to inner heliospheric effects and are not actually coronal in origin. This finding is consistent with previous observations and interpretations of SEP events connected westward of the associated flare.
ER -