@article{Lario:2026:1538-4357/ae2ea4,
author = {Lario, D and Hu, J and Balmaceda, LA and Kwon, RY and Wallace, S and da, Silva DE and Mays, ML and Krupar, V and Carcaboso, F and Warmuth, A and Stiefel, MZ and Khoo, LY and Richardson, IG and Kühl, P and Wimmer-Schweingruber, RF and Vainio, R and Riihonen, E and Liu, W and Aran, A and Paouris, E and Kane, MR and Lee, CO and Sasso, C and Arge, CN and Jones, SI and Verniero, J and Niemela, AE and Horbury, TS and Maksimovic, M},
doi = {1538-4357/ae2ea4},
journal = {Astrophysical Journal},
title = {The Major Solar Energetic Particle Event on 2024 May 20: Multispacecraft Observations of a Long-lasting Energetic Particle Reservoir},
url = {http://dx.doi.org/10.3847/1538-4357/ae2ea4},
volume = {998},
year = {2026}
}

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TY  - JOUR
AB  - The fleet of spacecraft distributed across the inner heliosphere during 2024 May–June provided a unique opportunity to analyze, over a broad range of heliolongitudes, the effects produced by the complex sunspot group associated with Active Region 13664. The intense solar activity from 2024 May 8 to 2024 June 21 produced unusually elevated solar energetic particle (SEP) intensities observed at heliocentric distances 1 au by Solar Orbiter, Parker Solar Probe, STEREO-A, and near-Earth spacecraft. This activity resulted in a >40 day period of enhanced 10 MeV proton intensities spanning at least ∼170° in longitude. Among these events, the 2024 May 20 SEP event was remarkable for its high intensity and wide spatial extent. It was associated with a fast (1500 km s<sup>−1</sup>) halo coronal mass ejection (CME) and an X16.5 solar flare located ∼171° in longitude from Earth. Near Earth, the event produced a long-lasting ∼100 MeV proton intensity enhancement with energy spectra flattening between 30 and 80 MeV. It also led to the formation of an energetic particle reservoir that persisted for ∼2 weeks and extended across at least ∼170° in longitude. Several mechanisms contributed to the broad longitudinal spread of SEPs and formation of the energetic particle reservoir, including acceleration at an extended CME-driven shock, particle drifts along the heliospheric current sheet, particle reflection and redistribution caused by the merging of preceding CMEs beyond 1 au, and predominantly cross-field particle transport processes.
AU  - Lario,D
AU  - Hu,J
AU  - Balmaceda,LA
AU  - Kwon,RY
AU  - Wallace,S
AU  - da,Silva DE
AU  - Mays,ML
AU  - Krupar,V
AU  - Carcaboso,F
AU  - Warmuth,A
AU  - Stiefel,MZ
AU  - Khoo,LY
AU  - Richardson,IG
AU  - Kühl,P
AU  - Wimmer-Schweingruber,RF
AU  - Vainio,R
AU  - Riihonen,E
AU  - Liu,W
AU  - Aran,A
AU  - Paouris,E
AU  - Kane,MR
AU  - Lee,CO
AU  - Sasso,C
AU  - Arge,CN
AU  - Jones,SI
AU  - Verniero,J
AU  - Niemela,AE
AU  - Horbury,TS
AU  - Maksimovic,M
DO  - 1538-4357/ae2ea4
PY  - 2026///
SN  - 0004-637X
TI  - The Major Solar Energetic Particle Event on 2024 May 20: Multispacecraft Observations of a Long-lasting Energetic Particle Reservoir
T2  - Astrophysical Journal
UR  - http://dx.doi.org/10.3847/1538-4357/ae2ea4
VL  - 998
ER  - 

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