[ { "id": "authors:cxbxz-6a886", "collection": "authors", "collection_id": "cxbxz-6a886", "cite_using_url": "https://authors.library.caltech.edu/records/cxbxz-6a886", "type": "article", "title": "Shock Properties for Solar Energetic Particle Events with Signatures of Inverse Velocity Arrival", "author": [ { "family_name": "Kouloumvakos", "given_name": "A.", "orcid": "0000-0001-6589-4509" }, { "family_name": "Lario", "given_name": "D.", "orcid": "0000-0002-3176-8704" }, { "family_name": "Mason", "given_name": "G. M.", "orcid": "0000-0003-2169-9618" }, { "family_name": "Vourlidas", "given_name": "A.", "orcid": "0000-0002-8164-5948" }, { "family_name": "Allen", "given_name": "R. C.", "orcid": "0000-0003-2079-5683" }, { "family_name": "Wijsen", "given_name": "N.", "orcid": "0000-0001-6344-6956" }, { "family_name": "Chen", "given_name": "X.", "orcid": "0000-0003-2865-1772" }, { "family_name": "Ding", "given_name": "Z.", "orcid": "0000-0002-9829-3811" }, { "family_name": "Jebaraj", "given_name": "I. C.", "orcid": "0000-0002-0606-7172" }, { "family_name": "Riley", "given_name": "P.", "orcid": "0000-0002-1859-456X" }, { "family_name": "McComas", "given_name": "D. J.", "orcid": "0000-0001-6160-1158" }, { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-Christina-M" }, { "family_name": "Paouris", "given_name": "E.", "orcid": "0000-0002-8387-5202" }, { "family_name": "Raptis", "given_name": "S.", "orcid": "0000-0002-4381-3197" }, { "family_name": "Rodr\u00edguez-Garc\u00eda", "given_name": "L.", "orcid": "0000-0003-2361-5510" }, { "family_name": "Xu", "given_name": "Z. G.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Berland", "given_name": "G. D.", "orcid": "0000-0001-6010-6374" }, { "family_name": "Ho", "given_name": "G. C.", "orcid": "0000-0003-1093-2066" }, { "family_name": "Mitchell", "given_name": "D. G.", "orcid": "0000-0003-1960-2119" }, { "family_name": "Roelof", "given_name": "E. C.", "orcid": "0000-0002-2270-0652" }, { "family_name": "Rodriguez-Pacheco", "given_name": "J.", "orcid": "0000-0002-4240-1115" }, { "family_name": "Hill", "given_name": "M. E.", "orcid": "0000-0002-5674-4936" }, { "family_name": "Wimmer-Schweingruber", "given_name": "R. F.", "orcid": "0000-0002-7388-173X" } ], "abstract": "

We present a detailed investigation of the shock properties associated with solar energetic particle (SEP) events that exhibit a concave (\"nose-like\") shape in their energy spectrogram, characterized by inverse velocity arrival (IVA) of the particles, where high-energy particles arrive later than mid-energy ones. Using measurements from Solar Orbiter and Parker Solar Probe between 2018 and 2025, we identify 26 such SEP events and reconstruct the observed shock fronts in three dimensions. We derive shock parameters along the magnetic field lines connected to each spacecraft using kinematic modeling and coronal magnetohydrodynamic simulations. Our analysis indicates that IVA-SEP events arise due to the spatial and temporal evolution of the shock properties and magnetic connectivity. In most of the cases analyzed here, the magnetic connectivity starts on the flanks of coronal mass ejection-driven shocks, where shocks tend to be weak, and shifts toward the shock apex, sampling stronger portions of the shock front. This evolution of the shock properties at the connected field lines likely leads to the delayed arrival of high-energy particles and the progressive hardening of the SEP energy spectrum, observed in some of the events. We find a correlation between the transition energy at which the IVA begins and the shock speed along the connected field lines, consistent with expectations from time-dependent diffusive shock acceleration. Our results underscore the importance of the evolving shock properties, magnetic connectivity, and instrumental sensitivity in shaping SEP intensity profiles and the formation of IVA signatures.

", "doi": "10.3847/1538-4357/ae5e65", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2026-05-10", "series_number": "2", "volume": "1002", "issue": "2", "pages": "188" }, { "id": "authors:kwrtf-99870", "collection": "authors", "collection_id": "kwrtf-99870", "cite_using_url": "https://authors.library.caltech.edu/records/kwrtf-99870", "type": "article", "title": "Anomalous cosmic rays within the inner heliosphere: Observations of helium by the High Energy Telescope on board Solar Orbiter", "author": [ { "family_name": "Xu", "given_name": "Zigong", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Wimmer-Schweingruber", "given_name": "Robert F.", "orcid": "0000-0002-7388-173X" }, { "family_name": "Berger", "given_name": "Lars", "orcid": "0009-0007-6389-8443" }, { "family_name": "K\u00fchl", "given_name": "Patrick", "orcid": "0000-0002-3758-9272" }, { "family_name": "Kollhoff", "given_name": "Alexander", "orcid": "0000-0002-9471-5132" }, { "family_name": "Heber", "given_name": "Bernd", "orcid": "0000-0003-0960-5658" }, { "family_name": "B\u00f6ttcher", "given_name": "Stephan I." }, { "family_name": "Yang", "given_name": "Liu", "orcid": "0000-0002-6416-1538" }, { "family_name": "Heidrich-Meisner", "given_name": "Verena", "orcid": "0000-0003-3502-8778" }, { "family_name": "Strauss", "given_name": "Roelf Du Toit", "orcid": "0000-0002-0205-0808" }, { "family_name": "Gomez-Herrero", "given_name": "Ra\u00fal", "orcid": "0000-0002-5705-9236" }, { "family_name": "Rodriguez-Pacheco", "given_name": "Javier", "orcid": "0000-0002-4240-1115" }, { "family_name": "Pacheco", "given_name": "Daniel", "orcid": "0000-0002-6176-4077" }, { "family_name": "Leske", "given_name": "Richard A.", "orcid": "0000-0002-0156-2414", "clpid": "Leske-R-A" } ], "abstract": "

Context. The radial gradients of cosmic rays are key parameters in studies of the transport of particles in space. Solar Orbiter, launched on 2020 February 10, approaches the Sun approximately every half-a-year, with its closest perihelion distance of 0.29 au at the end of 2022 during the nominal mission phase. The two double-ended high-energy telescopes (HET) on board Solar Orbiter measure energetic particles in the energy range between a few MeV/nuc and a few hundreds of MeV/nuc. These particles are dominated by anomalous cosmic rays (ACRs) and galactic cosmic rays (GCRs) during solar quiet times.

\n

Aims. By obtaining the radial gradient of ACR helium in the inner heliosphere, we can advance our understanding of how the transport of cosmic rays is affected by the particle drift effect and the large-scale magnetic field.

\n

Methods. We analyzed helium observations at Solar Orbiter/HET between 11.1 and 49 MeV/nuc. Since our study is focused on quiet time measurements, we removed the periods of solar energetic particle (SEP) events. The intensities were averaged over the Carrington rotation period. The helium observations from the Electron Proton and Helium Instrument (EPHIN) on board SOHO were utilized as the baseline to correct the long-term variation caused by the solar modulations.

\n

Results. We present the first observation of ACR helium at Solar Orbiter/HET between February 2020 and July 2022 in the inner heliosphere before the sun became fully active. We derived a radial gradient of ACR helium of between 0.3 and 1 au. The averaged radial gradient between 11.1 and 49 MeV/nuc is about 22 ± 4%/au and the averaged value between 11.1 and 41.2 MeV/nuc was raised to 32 ± 8%/au after removing the GCR contribution, which was estimated using a GCR model. In addition, the temporal variation of radial gradients indicates that gradients tend to increase with the enhancement of the solar modulation and the increased tilt angle of the heliospheric current sheet.

", "doi": "10.1051/0004-6361/202558218", "issn": "0004-6361", "publisher": "EDP Sciences", "publication": "Astronomy & Astrophysics", "publication_date": "2026-04", "volume": "708", "pages": "A36" }, { "id": "authors:e0xsm-3yq63", "collection": "authors", "collection_id": "e0xsm-3yq63", "cite_using_url": "https://authors.library.caltech.edu/records/e0xsm-3yq63", "type": "article", "title": "A galactic cosmic ray cavity in Earth-Moon space", "author": [ { "family_name": "Shang", "given_name": "Wensai", "orcid": "0000-0002-7078-8249" }, { "family_name": "Liu", "given_name": "Ji", "orcid": "0000-0001-6648-8908" }, { "family_name": "Xu", "given_name": "Zigong", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Yue", "given_name": "Chao", "orcid": "0000-0001-9720-5210" }, { "family_name": "Guo", "given_name": "Ruilong", "orcid": "0000-0002-7125-0942" }, { "family_name": "Xiao", "given_name": "Chao", "orcid": "0000-0002-2633-9526" }, { "family_name": "Shi", "given_name": "Quanqi", "orcid": "0000-0001-6835-4751" }, { "family_name": "Wimmer-Schweingruber", "given_name": "Robert F.", "orcid": "0000-0002-7388-173X" }, { "family_name": "Guo", "given_name": "Jingnan", "orcid": "0000-0002-8707-076X" }, { "family_name": "Degeling", "given_name": "Alexander W.", "orcid": "0000-0001-7338-9270" }, { "family_name": "Rankin", "given_name": "Robert" }, { "family_name": "Tian", "given_name": "Anmin" }, { "family_name": "Zong", "given_name": "Qiu-Gang" }, { "family_name": "Han", "given_name": "Chenyao", "orcid": "0009-0008-6476-0734" }, { "family_name": "Park", "given_name": "Jong-Sun", "orcid": "0000-0002-2732-1168" }, { "family_name": "Wang", "given_name": "Huizi", "orcid": "0000-0002-3652-6210" }, { "family_name": "Liu", "given_name": "Wenlong" }, { "family_name": "Fu", "given_name": "Suiyan", "orcid": "0000-0002-3858-1555" }, { "family_name": "Zhai", "given_name": "L. M.", "orcid": "0000-0002-7294-9691" }, { "family_name": "Chen", "given_name": "D.", "orcid": "0000-0002-6109-0113" }, { "family_name": "Ni", "given_name": "Sulan", "orcid": "0000-0002-2873-0860" }, { "family_name": "Chen", "given_name": "T. L.", "orcid": "0000-0002-2944-2422" } ], "abstract": "

In regions of the Solar System distant from planetary magnetic fields, galactic cosmic rays (GCRs) have generally been assumed to be uniformly distributed over the Earth-Moon distance. However, our analysis of data from the LND (Lunar Lander Neutron and Dosimetry) experiment onboard the Chang'E-4 lander revealed a region of reduced GCR flux in the prenoon sector of the lunar orbit. Further investigation suggests the presence of an energetic particle cavity, formed by Earth's magnetic field acting as an obstacle to GCR propagation. This cavity indicates that the influence of Earth's magnetic field within the space environment extends unexpectedly up to and far beyond the lunar orbit. This finding offers the potential to avoid high radiation levels during future lunar exploration and deep-space missions.

", "doi": "10.1126/sciadv.adv1908", "pmcid": "PMC13015879", "issn": "2375-2548", "publisher": "American Association for the Advancement of Science", "publication": "Science Advances", "publication_date": "2026-03-27", "series_number": "13", "volume": "12", "issue": "13", "pages": "eadv1908" }, { "id": "authors:ktkxr-gfy58", "collection": "authors", "collection_id": "ktkxr-gfy58", "cite_using_url": "https://authors.library.caltech.edu/records/ktkxr-gfy58", "type": "article", "title": "The 2024 July 23 Event: A Case Study of a Multispacecraft, Fe-rich Solar Energetic Particle Event", "author": [ { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-C-M-S" }, { "family_name": "Mason", "given_name": "G. M.", "orcid": "0000-0003-2169-9618" }, { "family_name": "Berland", "given_name": "G. D.", "orcid": "0000-0001-6010-6374" }, { "family_name": "Christian", "given_name": "E. R.", "orcid": "0000-0003-2134-3937" }, { "family_name": "Leske", "given_name": "R. A.", "orcid": "0000-0002-0156-2414", "clpid": "Leske-R-A" }, { "family_name": "McComas", "given_name": "D. J.", "orcid": "0000-0001-6160-1158" }, { "family_name": "McNutt", "given_name": "R. L.", "orcid": "0000-0002-4722-9166" }, { "family_name": "Mitchell", "given_name": "D. G.", "orcid": "0000-0003-1960-2119" }, { "family_name": "Muro", "given_name": "G. D.", "orcid": "0000-0003-0581-1278", "clpid": "Muro-Gabriel-D" }, { "family_name": "Pak", "given_name": "S.", "orcid": "0000-0003-2847-7110" }, { "family_name": "Schwadron", "given_name": "N. A.", "orcid": "0000-0002-3737-9283" }, { "family_name": "Wiedenbeck", "given_name": "M. E.", "orcid": "0000-0002-2825-3128", "clpid": "Wiedenbeck-Mark-E" }, { "family_name": "Xu", "given_name": "Z. G.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Ho", "given_name": "G. C.", "orcid": "0000-0003-1093-2066" }, { "family_name": "Wimmer-Schweingr\u00fcber", "given_name": "R. F.", "orcid": "0000-0002-7388-173X" } ], "abstract": "
\n

Occasionally, solar energetic particle (SEP) events associated with fast, wide coronal mass ejections (CMEs) driving interplanetary shocks exhibit Fe/O abundance ratios that are significantly higher than the nominal value of 0.134. The cause of this enrichment in Fe remains unclear, but there are two prevailing theories: contribution from flare-accelerated material, and reacceleration of suprathermal remnant flare material by a quasiperpendicular shock. The 2024 July 23 SEP event was observed by four spacecraft spread over ∼160° of solar longitude and 0.4 au in radial distance. We examine the H, He, O, and Fe spectra and He/H and Fe/O abundance ratios observed at each spacecraft, and find that three measured Fe/O ratios >0.6 were relatively independent of energy. The fourth spacecraft measured strongly energy-dependent Fe/O ratios reaching very low values of 0.02 at a few MeV nuc−1. In an effort to evaluate the plausibility of the two explanations for Fe-rich SEP events, we studied the magnetic connection of the spacecraft to the solar source and the evolving CME; the velocity dispersion of the first arriving particles; and the time evolution of the Fe/O ratios. We also noted the pre-event CME and flare activity. We find that neither scenario is clearly consistent with the compositional variations between the four spacecraft, but more detailed modeling of the magnetic connections between the spacecraft and the solar source and the propagating shock may be beneficial.

\n
", "doi": "10.3847/1538-4357/ae3f23", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2026-03-10", "series_number": "2", "volume": "999", "issue": "2", "pages": "209" }, { "id": "authors:pdxtg-n0e58", "collection": "authors", "collection_id": "pdxtg-n0e58", "cite_using_url": "https://authors.library.caltech.edu/records/pdxtg-n0e58", "type": "article", "title": "The High-Energy Ion Telescope (HIT) for the Interstellar Mapping And Acceleration Probe (IMAP) Mission", "author": [ { "family_name": "Christian", "given_name": "E. R.", "orcid": "0000-0003-2134-3937", "clpid": "Christian-E-R" }, { "family_name": "Mitchell", "given_name": "J. G.", "clpid": "Mitchell-J-G" }, { "family_name": "Bruno", "given_name": "A.", "clpid": "Bruno-A" }, { "family_name": "Albaijes", "given_name": "D.", "clpid": "Albaijes-D" }, { "family_name": "Bailey\u00a0Newman", "given_name": "S.", "clpid": "Bailey-Newman-S" }, { "family_name": "Boggs", "given_name": "R. C.", "clpid": "Boggs-R-C" }, { "family_name": "Choi", "given_name": "M. K.", "clpid": "Choi-M-K" }, { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-Christina-M" }, { "family_name": "Cook", "given_name": "W. R.", "clpid": "Cook-Walter-Richardson-III" }, { "family_name": "Darwish", "given_name": "Y. S.", "clpid": "Darwish-Y-S" }, { "family_name": "Davis", "given_name": "A. J.", "orcid": "0000-0002-9922-8915", "clpid": "Davis-Andrew-J" }, { "family_name": "de Nolfo", "given_name": "G. A.", "clpid": "de-Nolfo-G-A" }, { "family_name": "Dumonthier", "given_name": "J. J.", "clpid": "Dumonthier-J-J" }, { "family_name": "Garnett", "given_name": "R. D.", "clpid": "Garnett-R-D" }, { "family_name": "Gkioulidou", "given_name": "M.", "clpid": "Gkioulidou-M" }, { "family_name": "Gregory", "given_name": "K. J.", "clpid": "Gregory-K-J" }, { "family_name": "Guzman\u00a0Garcia", "given_name": "D.", "clpid": "Guzman--Garcia-D" }, { "family_name": "Haas", "given_name": "J. P.", "clpid": "Haas-J-P" }, { "family_name": "Hollenhorst", "given_name": "C.", "clpid": "Hollenhorst-C" }, { "family_name": "Jeunon", "given_name": "M.", "clpid": "Jeunon-M" }, { "family_name": "Kaiser", "given_name": "M. A.", "clpid": "Kaiser-M-A" }, { "family_name": "Kanekal", "given_name": "S. G.", "clpid": "Kanekal-S-G" }, { "family_name": "Kecman", "given_name": "B.", "clpid": "Kecman-Branislav" }, { "family_name": "Leske", "given_name": "Richard A.", "orcid": "0000-0002-0156-2414", "clpid": "Leske-R-A" }, { "family_name": "Letzer", "given_name": "J. D.", "clpid": "Letzer-J-D" }, { "family_name": "Liceaga\u00a0Indart", "given_name": "I.", "clpid": "Liceaga-Indart-I" }, { "family_name": "McComas", "given_name": "D. J.", "clpid": "McComas-D-J" }, { "family_name": "McNeel", "given_name": "B.", "clpid": "McNeel-B" }, { "family_name": "Muro", "given_name": "G. D.", "orcid": "0000-0003-0581-1278", "clpid": "Muro-Gabriel-D" }, { "family_name": "Nolan", "given_name": "J. T.", "clpid": "Nolan-J-T" }, { "family_name": "Ogindo", "given_name": "M.", "clpid": "Ogindo-M" }, { "family_name": "Petrowich", "given_name": "P.", "clpid": "Petrowich-P" }, { "family_name": "Reaves", "given_name": "W. J.", "clpid": "Reaves-W-J" }, { "family_name": "Rosnack", "given_name": "T. P.", "clpid": "Rosnack-T-P" }, { "family_name": "Saghafi", "given_name": "N.", "clpid": "Saghafi-N" }, { "family_name": "Salerno", "given_name": "C. L.", "clpid": "Salerno-C-L" }, { "family_name": "Schwadron", "given_name": "N. A.", "clpid": "Schwadron-N-A" }, { "family_name": "Silber", "given_name": "M. A.", "clpid": "Silber-M-A" }, { "family_name": "Smith", "given_name": "E. S.", "clpid": "Smith-E-S" }, { "family_name": "Smith", "given_name": "M. T.", "clpid": "Smith-M-T" }, { "family_name": "Su\u00e1rez", "given_name": "G.", "clpid": "Su\u00e1rez-G" }, { "family_name": "Tatoli", "given_name": "T.", "clpid": "Tatoli-T" }, { "family_name": "Tiu", "given_name": "C. P.", "clpid": "Tiu-C-P" }, { "family_name": "Wiedenbeck", "given_name": "Mark Edward", "orcid": "0000-0002-2825-3128", "clpid": "Wiedenbeck-M-E" }, { "family_name": "Windhausen", "given_name": "M. H.", "clpid": "Windhausen-M-H" }, { "family_name": "Xu", "given_name": "Z.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" } ], "abstract": "

The Interstellar Mapping and Acceleration Probe (IMAP; McComas et al. in Space Sci Rev 214:116, 2018a; McComas et al. in Space Sci Rev 221:100, 2025) is a NASA mission designed to study two of the most important issues in heliophysics: the interaction of the solar wind with the local interstellar medium and the acceleration of energetic particles. These two puzzles are surprisingly intertwined because particle acceleration in the inner heliosphere plays a large role in the interactions at the edge of the heliosphere. The ten instruments on IMAP, situated near the Earth-Sun L1 Lagrange point, include both in situ and remote-sensing observations and are designed to work together to explore these questions. The High-energy Ion Telescope (HIT), described herein, measures in situ ions from hydrogen through nickel at energies ranging from a few MeV/nucleon to some tens of MeV/nucleon, depending upon species. While the primary focus of HIT is Solar Energetic Particles (SEPs), HIT is also sensitive to Anomalous Cosmic Rays (ACRs) and Galactic Cosmic Rays (GCRs) that are also present at these energies. Working with the other IMAP instruments, HIT studies how the variation in SEP intensities, spectra, anisotropies, and composition inform the acceleration processes that generate these particles, and, in turn, how these high-energy particles affect the outer heliosphere. This paper details the design and operation of the HIT instrument.

", "doi": "10.1007/s11214-026-01279-6", "issn": "0038-6308", "publisher": "Springer Science and Business Media LLC", "publication": "Space Science Reviews", "publication_date": "2026-02-27", "volume": "222", "pages": "23" }, { "id": "authors:qb3df-87p74", "collection": "authors", "collection_id": "qb3df-87p74", "cite_using_url": "https://authors.library.caltech.edu/records/qb3df-87p74", "type": "article", "title": "Parker Solar Probe Observations of Suprathermal and Energetic Particles during Orbits 18 and 19", "author": [ { "family_name": "Berland", "given_name": "G. D.", "orcid": "0000-0001-6010-6374" }, { "family_name": "Hill", "given_name": "M. E.", "orcid": "0000-0002-5674-4936" }, { "family_name": "Kouloumvakos", "given_name": "A.", "orcid": "0000-0001-6589-4509" }, { "family_name": "Mitchell", "given_name": "D. G.", "orcid": "0000-0003-1960-2119" }, { "family_name": "McNutt", "given_name": "R. L.", "orcid": "0000-0002-4722-9166" }, { "family_name": "Roelof", "given_name": "E. C.", "orcid": "0000-0002-2270-0652" }, { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-C-M-S" }, { "family_name": "Wiedenbeck", "given_name": "M. E.", "orcid": "0000-0002-2825-3128", "clpid": "Wiedenbeck-Mark-E" }, { "family_name": "McComas", "given_name": "D. J.", "orcid": "0000-0001-6160-1158" }, { "family_name": "Christian", "given_name": "E. R.", "orcid": "0000-0003-2134-3937" }, { "family_name": "Schwadron", "given_name": "N. A.", "orcid": "0000-0002-3737-9283" }, { "family_name": "Khoo", "given_name": "L. Y.", "orcid": "0000-0003-0412-1064" }, { "family_name": "Cuesta", "given_name": "M. E.", "orcid": "0000-0002-7341-2992" }, { "family_name": "Muro", "given_name": "G. D.", "orcid": "0000-0003-0581-1278", "clpid": "Muro-Gabriel-D" }, { "family_name": "Xu", "given_name": "Z. G.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Pak", "given_name": "S.", "orcid": "0000-0003-2847-7110" }, { "family_name": "Farooki", "given_name": "H. A.", "orcid": "0000-0001-7952-8032" }, { "family_name": "Stevens", "given_name": "M. L.", "orcid": "0000-0002-7728-0085" }, { "family_name": "Bale", "given_name": "S. D.", "orcid": "0000-0002-1989-3596" } ], "abstract": "
\n

The Parker Solar Probe Integrated Science Investigation of the Sun (IS\u2299IS) instrument suite measured a variety of suprathermal and energetic particle events during orbits 18 and 19. We provide an overview of key features of the observations to provide guidance critical to making progress on complicated, integrated data sets like those provided by IS\u2299IS. In this work, we analyze and describe observations of particle acceleration signatures associated with coronal mass ejection (CME)–driven shocks and solar flares from 2023 November to 2024 March as measured by the IS\u2299IS/Energetic Particle Instrument-Low Energy and Energetic Particle Instrument-High Energy particle detectors. We present energy spectra for protons through Fe ions from ∼10 keV nuc−1 to >10 MeV nuc−1, abundance ratios, and time series analyses for seven solar energetic particle (SEP) events with respect to the magnetic field and plasma context provided by the FIELDS and Solar Wind Electrons Alphas and Protons instruments, respectively. For SEP events in orbits 18 and 19, we find that acceleration driven by multiple CMEs in succession have larger variability in 4He/H and Fe/O ratios than singular CMEs, that flare-associated SEP events preferentially accelerate higher mass-to-charge ratio particles, and that shock upstream transients may be present in CME-driven interplanetary shocks.

\n
", "doi": "10.3847/1538-4357/ae1b97", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2026-01-01", "series_number": "1", "volume": "996", "issue": "1", "pages": "11" }, { "id": "authors:gbmd3-b4a08", "collection": "authors", "collection_id": "gbmd3-b4a08", "cite_using_url": "https://authors.library.caltech.edu/records/gbmd3-b4a08", "type": "article", "title": "Delayed maximum energy solar energetic particle events. Statistical analysis from Solar Orbiter", "author": [ { "family_name": "Allen", "given_name": "R. C.", "orcid": "0000-0003-2079-5683" }, { "family_name": "Ho", "given_name": "G. C.", "orcid": "0000-0003-1093-2066" }, { "family_name": "Mason", "given_name": "G. M.", "orcid": "0000-0003-2169-9618" }, { "family_name": "Ding", "given_name": "Z.", "orcid": "0000-0002-9829-3811" }, { "family_name": "Walker", "given_name": "M. H.", "orcid": "0000-0003-4380-3519" }, { "family_name": "Kouloumvakos", "given_name": "A.", "orcid": "0000-0001-6589-4509" }, { "family_name": "Wimmer-Schweingruber", "given_name": "R. F.", "orcid": "0000-0002-7388-173X" }, { "family_name": "Rodriguez-Pacheco", "given_name": "J.", "orcid": "0000-0002-4240-1115" }, { "family_name": "Vines", "given_name": "S. K.", "orcid": "0000-0002-7515-3285" }, { "family_name": "Filwett", "given_name": "R. J.", "orcid": "0000-0002-5497-7867" }, { "family_name": "Xu", "given_name": "Z.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-C-M-S" } ], "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.

", "doi": "10.1051/0004-6361/202557079", "issn": "0004-6361", "publisher": "EDP Sciences", "publication": "Astronomy & Astrophysics", "publication_date": "2026-01", "volume": "705", "pages": "A126" }, { "id": "authors:118ne-2r740", "collection": "authors", "collection_id": "118ne-2r740", "cite_using_url": "https://authors.library.caltech.edu/records/118ne-2r740", "type": "article", "title": "Local Particle Acceleration in an ICME-in-Sheath Structure Observed by Solar Orbiter", "author": [ { "family_name": "Chen", "given_name": "Xiaomin", "orcid": "0009-0003-3760-705X" }, { "family_name": "Li", "given_name": "Chuan", "orcid": "0000-0001-7693-4908" }, { "family_name": "Xu", "given_name": "Zigong", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Nicolaou", "given_name": "Georgios", "orcid": "0000-0003-3623-4928" }, { "family_name": "Kollhoff", "given_name": "Alexander", "orcid": "0000-0002-9471-5132" }, { "family_name": "Ho", "given_name": "George C.", "orcid": "0000-0003-1093-2066" }, { "family_name": "Wimmer-Schweingruber", "given_name": "Robert F.", "orcid": "0000-0002-7388-173X" }, { "family_name": "Owen", "given_name": "Christopher J.", "orcid": "0000-0002-5982-4667" } ], "abstract": "
\n

Local particle acceleration in the shock sheath region formed during the interaction between multiple coronal mass ejections (CMEs) is a complicated process that is still under investigation. On 2024 March 23, the successive eruption of two magnetic flux ropes from the solar active region 3614 produced twin CMEs, as identified in coronagraph images. By analyzing in situ data from Solar Orbiter and Wind, it is found that the primary interplanetary CME (ICME)-driven shock overtook the preceding ICME, trapping it in the sheath between the shock and the primary ICME, forming the ICME-in-sheath (IIS) structure. Using Solar Orbiter observations, we show that both electrons and ions are accelerated within the IIS. A clear enhancement of suprathermal electrons was observed at the IIS boundary, where strong flow shear and large magnetic field variation suggest possible local electron acceleration. Electrons (>38 keV) exhibit a long-lasting enhancement in the IIS with a spectral index of ∼2.2, similar to that in the shock sheath and the primary ICME, indicating a similar solar origin. Inside both the sheath and IIS, spectra of protons and 4He are generally consistent with the prediction of the diffusive shock acceleration, whereas Fe and O present a double power-law shape. Additionally, the Fe/O ratio in the IIS is higher than that in the sheath, and closer to the abundance of the flare-related particles, suggesting the remnant particles of flare confined in the IIS.

\n
", "doi": "10.3847/1538-4357/ae1476", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2025-12-01", "series_number": "2", "volume": "994", "issue": "2", "pages": "211" }, { "id": "authors:t25hf-kjz79", "collection": "authors", "collection_id": "t25hf-kjz79", "cite_using_url": "https://authors.library.caltech.edu/records/t25hf-kjz79", "type": "article", "title": "Distinct Solar Energetic Particle Shock Intensity\u2013Diffusion Coefficient Relationships in the Inner Heliosphere", "author": [ { "family_name": "Cuesta", "given_name": "M. E.", "orcid": "0000-0002-7341-2992" }, { "family_name": "Fraschetti", "given_name": "F.", "orcid": "0000-0002-5456-4771" }, { "family_name": "Livadiotis", "given_name": "G.", "orcid": "0000-0002-7655-6019" }, { "family_name": "Farooki", "given_name": "H. A.", "orcid": "0000-0001-7952-8032" }, { "family_name": "Shen", "given_name": "M. M.", "orcid": "0000-0002-3093-458X" }, { "family_name": "Khoo", "given_name": "L. Y.", "orcid": "0000-0003-0412-1064" }, { "family_name": "Szalay", "given_name": "J. R.", "orcid": "0000-0003-2685-9801" }, { "family_name": "Rankin", "given_name": "J. S.", "orcid": "0000-0002-8111-1444" }, { "family_name": "McComas", "given_name": "D. J.", "orcid": "0000-0001-6160-1158" }, { "family_name": "Mitchell", "given_name": "D. G.", "orcid": "0000-0003-1960-2119" }, { "family_name": "Christian", "given_name": "E. R.", "orcid": "0000-0003-2134-3937" }, { "family_name": "Mitchell", "given_name": "J. G.", "orcid": "0000-0003-4501-5452" }, { "family_name": "Berland", "given_name": "G. D.", "orcid": "0000-0001-6010-6374" }, { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-C-M-S" }, { "family_name": "Leske", "given_name": "R. A.", "orcid": "0000-0002-0156-2414", "clpid": "Leske-R-A" }, { "family_name": "Xu", "given_name": "Z.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Muro", "given_name": "G. D.", "orcid": "0000-0003-0581-1278", "clpid": "Muro-Gabriel-D" }, { "family_name": "Pecora", "given_name": "F.", "orcid": "0000-0003-4168-590X" }, { "family_name": "Ruffolo", "given_name": "D.", "orcid": "0000-0003-3414-9666" }, { "family_name": "Matthaeus", "given_name": "W. H.", "orcid": "0000-0001-7224-6024" }, { "family_name": "Giacalone", "given_name": "J.", "orcid": "0000-0002-0850-4233" }, { "family_name": "Schwadron", "given_name": "N. A.", "orcid": "0000-0002-3737-9283" }, { "family_name": "Desai", "given_name": "M. I.", "orcid": "0000-0002-7318-6008" }, { "family_name": "Dayeh", "given_name": "M. A.", "orcid": "0000-0001-9323-1200" }, { "family_name": "Bale", "given_name": "S. D.", "orcid": "0000-0002-1989-3596" }, { "family_name": "Stevens", "given_name": "M. L.", "orcid": "0000-0002-7728-0085" }, { "family_name": "Livi", "given_name": "R.", "orcid": "0000-0002-0396-0547" } ], "abstract": "
\n

It has been inferred from theory that the spatial diffusion coefficient (κ) upstream of shocks is anticorrelated with the intensity of solar energetic particles (SEPs) at the shock (jshock) motivated by quasi-linear theory (QLT). This is because a lower κ along the magnetic field (κ\u2225) implies that particles are trapped for longer, providing more acceleration and resulting in a higher jshock. However, the simplest version of DSA predicts that jshock is determined by the source of the injected population at the shock and plasma density jump with no relation to κ for low-energy SEPs. Here, we identify the relationship between κ and jshock, whose form is unknown, using Parker Solar Probe observations of eight shocks within 1 au. We estimate a characteristic κfit along the shock normal by fitting the upstream SEP intensity profiles with a 1D steady-state transport model for acceleration and escape assuming pitch-angle isotropy in the plasma frame. Also, we estimate κ\u2225 based on the magnetic power spectral density using QLT for comparison with κfit. Our results show that both quantities are anticorrelated with jshock. Instead of a uniform relationship between κ and jshock, we find distinct relationships appearing as potential power laws manifested across SEP events with no obvious radial dependence from 0.07 to 0.74 au. These relationships may be grouped by similar shock parameters (in terms of speed, strength, and orientation). Our findings raise questions about SEP transport and its radial dependence within 1 au and provide important observational constraints for models of shock-accelerated particles.

\n
", "doi": "10.3847/2041-8213/ae109c", "issn": "2041-8205", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal Letters", "publication_date": "2025-11-01", "series_number": "1", "volume": "993", "issue": "1", "pages": "L15" }, { "id": "authors:795d6-vyb31", "collection": "authors", "collection_id": "795d6-vyb31", "cite_using_url": "https://authors.library.caltech.edu/records/795d6-vyb31", "type": "article", "title": "Investigation of the inverse velocity dispersion in a solar energetic particle event observed by Solar Orbiter", "author": [ { "family_name": "Ding", "given_name": "Zheyi", "orcid": "0000-0002-9829-3811" }, { "family_name": "Wimmer-Schweingruber", "given_name": "Robert F.", "orcid": "0000-0002-7388-173X" }, { "family_name": "Kollhoff", "given_name": "Alexander", "orcid": "0000-0002-9471-5132" }, { "family_name": "K\u00fchl", "given_name": "Patrick", "orcid": "0000-0002-3758-9272" }, { "family_name": "Yang", "given_name": "Liu", "orcid": "0000-0002-6416-1538" }, { "family_name": "Berger", "given_name": "Lars" }, { "family_name": "Kouloumvakos", "given_name": "Athanasios", "orcid": "0000-0001-6589-4509" }, { "family_name": "Wijsen", "given_name": "Nicolas", "orcid": "0000-0001-6344-6956" }, { "family_name": "Guo", "given_name": "Jingnan", "orcid": "0000-0002-8707-076X" }, { "family_name": "Pacheco", "given_name": "Daniel", "orcid": "0000-0002-6176-4077" }, { "family_name": "Li", "given_name": "Yuncong", "orcid": "0009-0006-5022-9964" }, { "family_name": "Temmer", "given_name": "Manuela", "orcid": "0000-0003-4867-7558" }, { "family_name": "Rodriguez-Pacheco", "given_name": "Javier", "orcid": "0000-0002-4240-1115" }, { "family_name": "Allen", "given_name": "Robert C.", "orcid": "0000-0003-2079-5683" }, { "family_name": "Ho", "given_name": "George C.", "orcid": "0000-0003-1093-2066" }, { "family_name": "Mason", "given_name": "Glenn M.", "orcid": "0000-0003-2169-9618" }, { "family_name": "Xu", "given_name": "Zigong", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Gunaseelan", "given_name": "Sindhuja" } ], "abstract": "

Context. Solar energetic particle (SEP) events provide crucial insights into particle acceleration and transport mechanisms in the heliosphere. Inverse velocity dispersion (IVD) events, characterized by higher-energy particles that arrive later than lower-energy particles, challenge the classical understanding of SEP events and are increasingly observed by spacecraft, such as Parker Solar Probe and Solar Orbiter. However, the mechanisms underlying IVD events remain poorly understood.

\n

Aims. We investigate the physical processes that cause long-duration IVD events by analyzing the SEP event observed by Solar Orbiter on 2022 June 7. We explore the role of evolving shock connectivity, particle acceleration at interplanetary (IP) shocks, and cross-field transport in shaping the observed particle profiles.

\n

Methods. We used data from the Energetic Particle Detector (EPD) suite on board Solar Orbiter to analyze the characteristics of the IVD, and we modeled the event using the heliospheric energetic particle acceleration and transport (HEPAT) model. The simulations tracked evolutions of shock properties, particle acceleration and transport to assess the influence of shock expansion, shock connectivity, and transport processes on the formation of IVD events.

\n

Results. The IVD event exhibited a distinct and long-duration IVD signature across proton energies from 1 to 20 MeV, and it lasted for approximately 10 hours. Heavy ions exhibited varying nose energies, defined as the energy corresponding to the first-arriving particles. Simulations suggest that evolving shock connectivity and the evolution of the shock play a primary role in the IVD signature. The magnetic connection shifts from the shock flank to the nose over time, which results in a gradual increase in the maximum particle energy along the field line. Furthermore, the model results show that limited cross-field diffusion can influence both the nose energy and the duration of the IVD event.

\n

Conclusions. This study demonstrates that long-duration IVD events are primarily driven by evolving magnetic connectivity along a nonuniform shock that evolves over time, where the connection moves to more efficient acceleration sites as the shock propagates farther from the Sun. Other mechanisms, such as the acceleration time at the shock, may also contribute to the observed IVD features. The interplay of these factors remains an open question that warrants further investigation in other events.

", "doi": "10.1051/0004-6361/202553806", "issn": "0004-6361", "publisher": "EDP Sciences", "publication": "Astronomy and Astrophysics", "publication_date": "2025-04", "volume": "696", "pages": "A199" }, { "id": "authors:4dejb-xz935", "collection": "authors", "collection_id": "4dejb-xz935", "cite_using_url": "https://authors.library.caltech.edu/records/4dejb-xz935", "type": "article", "title": "Radial Dependence of Ion Fluences in the 2023 July 17 Solar Energetic Particle Event from Parker Solar Probe to STEREO and ACE", "author": [ { "family_name": "Muro", "given_name": "G. D.", "orcid": "0000-0003-0581-1278", "clpid": "Muro-Gabriel-D" }, { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-C-M-S" }, { "family_name": "Xu", "given_name": "Z.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Leske", "given_name": "R. A.", "orcid": "0000-0002-0156-2414", "clpid": "Leske-R-A" }, { "family_name": "Christian", "given_name": "E. R.", "orcid": "0000-0003-2134-3937" }, { "family_name": "Cummings", "given_name": "A. C.", "orcid": "0000-0002-3840-7696", "clpid": "Cummings-A-C" }, { "family_name": "De Nolfo", "given_name": "G.", "orcid": "0000-0002-3677-074X" }, { "family_name": "Desai", "given_name": "M. I.", "orcid": "0000-0002-7318-6008" }, { "family_name": "Fraschetti", "given_name": "F.", "orcid": "0000-0002-5456-4771" }, { "family_name": "Giacalone", "given_name": "J.", "orcid": "0000-0002-0850-4233" }, { "family_name": "Labrador", "given_name": "A.", "orcid": "0000-0001-9178-5349", "clpid": "Labrador-Allan" }, { "family_name": "McComas", "given_name": "D. J.", "orcid": "0000-0001-6160-1158" }, { "family_name": "Mitchell", "given_name": "J. G.", "orcid": "0000-0003-4501-5452" }, { "family_name": "Mitchell", "given_name": "D. G.", "orcid": "0000-0003-1960-2119" }, { "family_name": "Rankin", "given_name": "J.", "orcid": "0000-0002-8111-1444" }, { "family_name": "Schwadron", "given_name": "N. A.", "orcid": "0000-0002-3737-9283" }, { "family_name": "Shen", "given_name": "M.", "orcid": "0000-0002-3093-458X" }, { "family_name": "Wiedenbeck", "given_name": "M. E.", "orcid": "0000-0002-2825-3128", "clpid": "Wiedenbeck-M-E" }, { "family_name": "Bale", "given_name": "S. D.", "orcid": "0000-0002-1989-3596" }, { "family_name": "Romeo", "given_name": "O.", "orcid": "0000-0002-4559-2199" }, { "family_name": "Vourlidas", "given_name": "A.", "orcid": "0000-0002-8164-5948" } ], "abstract": "
\n

In the latter moments of 2023 July 17, the solar active region (AR) 13363, near the southwestern face of the Sun, was undergoing considerable evolution, which resulted in a significant solar energetic particle (SEP) event measured by Parker Solar Probe’s Integrated Science Investigation of the Sun (IS\u2299IS) and near-Earth spacecraft. Remote observations from GOES and CHASE captured two M5.0+ solar flares that peaked at 23:34 and 00:06 UT from the source region. In tandem, STEREO COR2 first recorded a small, narrow coronal mass ejection (CME) emerging at 22:54 UT and then saw a major halo CME emerge at 23:43 UT with a bright, rapidly expanding core and CME-driven magnetic shock with an estimated speed of ∼1400 km s−1. Parker Solar Probe was positioned at 0.65 au, near-perfectly on the nominal Parker spiral magnetic field line, which connected Earth and the AR for a 537 km s−1 ambient solar wind speed at L1. This fortuitous alignment provided the opportunity to examine how the SEP velocity dispersion, energy spectra, elemental composition, and fluence varied from 0.65 to 1 au along a shared magnetic connection to the Sun. We find a strong radial gradient, which is best characterized for H and He as r−4.0, and most surprisingly, is stronger for O and Fe, which is better described by r−5.7.

\n
", "doi": "10.3847/1538-4357/adadf7", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2025-03-01", "series_number": "1", "volume": "981", "issue": "1", "pages": "8" }, { "id": "authors:vb2ea-1f635", "collection": "authors", "collection_id": "vb2ea-1f635", "cite_using_url": "https://authors.library.caltech.edu/records/vb2ea-1f635", "type": "article", "title": "Comparing Methods for Calculating Solar Energetic Particle Intensities: Rebinning versus Spectral Binning", "author": [ { "family_name": "Cuesta", "given_name": "M. E.", "orcid": "0000-0002-7341-2992" }, { "family_name": "Khoo", "given_name": "L. Y.", "orcid": "0000-0003-0412-1064" }, { "family_name": "Livadiotis", "given_name": "G.", "orcid": "0000-0002-7655-6019" }, { "family_name": "Shen", "given_name": "M. M.", "orcid": "0000-0002-3093-458X" }, { "family_name": "Szalay", "given_name": "J. R.", "orcid": "0000-0003-2685-9801" }, { "family_name": "McComas", "given_name": "D. J.", "orcid": "0000-0001-6160-1158" }, { "family_name": "Rankin", "given_name": "J. S.", "orcid": "0000-0002-8111-1444" }, { "family_name": "Bandyopadhyay", "given_name": "R.", "orcid": "0000-0002-6962-0959" }, { "family_name": "Farooki", "given_name": "H. A.", "orcid": "0000-0001-7952-8032" }, { "family_name": "Niehof", "given_name": "J. T.", "orcid": "0000-0001-6286-5809" }, { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-C-M-S" }, { "family_name": "Leske", "given_name": "Richard A.", "orcid": "0000-0002-0156-2414", "clpid": "Leske-R-A" }, { "family_name": "Xu", "given_name": "Z.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Christian", "given_name": "E. R.", "orcid": "0000-0003-2134-3937" }, { "family_name": "Desai", "given_name": "M. I.", "orcid": "0000-0002-7318-6008" }, { "family_name": "Dayeh", "given_name": "M. A.", "orcid": "0000-0001-9323-1200" } ], "abstract": "

Solar energetic particle (SEP) events have been observed for decades in the interplanetary medium by spacecraft measuring the intensity of energetic ions and electrons. These intensities provide valuable information about particle acceleration, the effects of bulk plasma dynamics on particle transport, and the anisotropy of particle distributions. Since measured intensities are typically reported in narrow energy bins, it is common to rebin intensities over a wider energy range to improve counting statistics. We investigate two methods for calculating intensities across multiple energy bins: (a) rebinned intensity (j\u2015linlin), which is calculated by integrating the intensity over energy space and corresponds to the intensity at an effective energy that depends on the time-varying spectral index, and (b) spectral binned intensity (j\u2015loglog), calculated by integrating the log intensity in log–energy space, yielding the intensity at the log-centered energy that is independent of the spectral index and remains constant over time. We compare these methods using Parker Solar Probe (PSP) IS\u2299IS measurements of energetic protons, and we prescribe criteria for selecting the appropriate method for different scenarios. Our results show that the rebinned intensity is consistently larger (up to a factor of 5) than the spectral binned intensity for two SEP events observed by PSP, although the time series of the two methods are strongly correlated. Overall, both measures are important for SEP spectral analysis, and the selection of the appropriate measure depends on whether a physical (spectral binned intensity) or a statistical (rebinned intensity) representation is needed for a given analysis.

", "doi": "10.3847/1538-4357/adaea9", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2025-02-20", "series_number": "2", "volume": "980", "issue": "2", "pages": "235" }, { "id": "authors:1yy58-ja209", "collection": "authors", "collection_id": "1yy58-ja209", "cite_using_url": "https://authors.library.caltech.edu/records/1yy58-ja209", "type": "article", "title": "Longitudinal Dependence of Heavy Ion Composition in the 2021 October 28 Ground Level Enhancement Event", "author": [ { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-C-M-S" }, { "family_name": "Mason", "given_name": "G. M.", "orcid": "0000-0003-2169-9618" }, { "family_name": "Christian", "given_name": "E. R.", "orcid": "0000-0003-2134-3937" }, { "family_name": "Cummings", "given_name": "A. C.", "orcid": "0000-0002-3840-7696", "clpid": "Cummings-A-C" }, { "family_name": "de Nolfo", "given_name": "G. A.", "orcid": "0000-0002-3677-074X" }, { "family_name": "Desai", "given_name": "M. I.", "orcid": "0000-0002-7318-6008" }, { "family_name": "Giacalone", "given_name": "J.", "orcid": "0000-0002-0850-4233" }, { "family_name": "Hill", "given_name": "M. E." }, { "family_name": "Labrador", "given_name": "A. W.", "orcid": "0000-0001-9178-5349", "clpid": "Labrador-A-W" }, { "family_name": "Leske", "given_name": "R. A.", "orcid": "0000-0002-0156-2414", "clpid": "Leske-R-A" }, { "family_name": "McComas", "given_name": "D. J.", "orcid": "0000-0001-6160-1158" }, { "family_name": "McNutt Jr", "given_name": "R. L.", "orcid": "0000-0002-4722-9166" }, { "family_name": "Mitchell", "given_name": "D. G.", "orcid": "0000-0003-1960-2119" }, { "family_name": "Mitchell", "given_name": "J. G.", "orcid": "0000-0003-4501-5452" }, { "family_name": "Muro", "given_name": "G. D.", "orcid": "0000-0003-0581-1278", "clpid": "Muro-Gabriel-D" }, { "family_name": "Rankin", "given_name": "J. S.", "orcid": "0000-0002-8111-1444" }, { "family_name": "Schwadron", "given_name": "N. A.", "orcid": "0000-0002-3737-9283" }, { "family_name": "Shen", "given_name": "M. M.", "orcid": "0000-0002-3093-458X" }, { "family_name": "Wiedenbeck", "given_name": "M. E.", "orcid": "0000-0002-2825-3128", "clpid": "Wiedenbeck-M-E" }, { "family_name": "Xu", "given_name": "Z. G.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Ho", "given_name": "G. C.", "orcid": "0000-0003-1093-2066" }, { "family_name": "Wimmer-Schweingr\u00fcber", "given_name": "R. F.", "orcid": "0000-0002-7388-173X" } ], "abstract": "
\n

The 2021 October 28 solar energetic particle (SEP) event was a rare ground level enhancement (GLE) event, where secondary particles from the interactions of SEPs with the Earth's atmosphere were detected by neutron monitors on the ground. A number of papers have examined the solar signatures, neutron monitor observations, and the characteristics of the SEP protons and electrons for this event. Here we describe the heavy ion signatures, specifically O and Fe, observed by multiple spacecraft. Parker Solar Probe, Solar Terrestrial Relations Observatory-Ahead, and Advanced Composition Explorer were distributed over nearly 60° in solar longitude and 0.4 au in heliocentric distance. Despite their separations, all three spacecraft measured event-integrated O and Fe spectra, well represented by power laws, with nearly the same power-law index of approximately −1.7, which is significantly harder than most large SEP events and many GLE events. Moreover, the Fe/O abundance ratio determined from these spectra was also found to be spatially invariant over the 60° in longitude and 0.4 au in heliocentric distance. Such near uniformity is highly unusual, and only one similar occurrence was found in a previous multispacecraft. The observed Fe/O ratio of 0.39 is higher than typical for large SEP events but not unusual for GLE events.

\n
", "doi": "10.3847/2041-8213/ada24b", "issn": "2041-8205", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal Letters", "publication_date": "2025-01-10", "series_number": "2", "volume": "978", "issue": "2", "pages": "L35" }, { "id": "authors:yhc38-3gd25", "collection": "authors", "collection_id": "yhc38-3gd25", "cite_using_url": "https://authors.library.caltech.edu/records/yhc38-3gd25", "type": "article", "title": "Observations of the 2022 September 5 Solar Energetic Particle Event at 15 Solar Radii", "author": [ { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-Chistina-M-S" }, { "family_name": "Leske", "given_name": "R. A.", "orcid": "0000-0002-0156-2414", "clpid": "Leske-Richard-A" }, { "family_name": "Christian", "given_name": "E. R.", "orcid": "0000-0003-2134-3937" }, { "family_name": "Cummings", "given_name": "A. C.", "orcid": "0000-0002-3840-7696", "clpid": "Cummings-Alan-C" }, { "family_name": "de Nolfo", "given_name": "G. A.", "orcid": "0000-0002-3677-074X" }, { "family_name": "Desai", "given_name": "M. I.", "orcid": "0000-0002-7318-6008" }, { "family_name": "Giacalone", "given_name": "J.", "orcid": "0000-0002-0850-4233" }, { "family_name": "Hill", "given_name": "M. E.", "orcid": "0000-0002-5674-4936" }, { "family_name": "Labrador", "given_name": "A. W.", "orcid": "0000-0001-9178-5349", "clpid": "Labrador-Allan-W" }, { "family_name": "McComas", "given_name": "D. J.", "orcid": "0000-0001-6160-1158" }, { "family_name": "McNutt", "given_name": "R. L.", "orcid": "0000-0002-4722-9166" }, { "family_name": "Mewaldt", "given_name": "R. A.", "orcid": "0000-0003-2178-9111", "clpid": "Mewaldt-Richard-A" }, { "family_name": "Mitchell", "given_name": "D. G.", "orcid": "0000-0003-1960-2119" }, { "family_name": "Mitchell", "given_name": "J. G.", "orcid": "0000-0003-4501-5452" }, { "family_name": "Muro", "given_name": "G. D.", "orcid": "0000-0003-0581-1278", "clpid": "Muro-Gabriel-D" }, { "family_name": "Rankin", "given_name": "J. S.", "orcid": "0000-0002-8111-1444" }, { "family_name": "Schwadron", "given_name": "N. A.", "orcid": "0000-0002-3737-9283" }, { "family_name": "Sharma", "given_name": "T." }, { "family_name": "Shen", "given_name": "M. M.", "orcid": "0000-0002-3093-458X" }, { "family_name": "Szalay", "given_name": "J. R.", "orcid": "0000-0003-2685-9801" }, { "family_name": "Wiedenbeck", "given_name": "M. E.", "orcid": "0000-0002-2825-3128", "clpid": "Wiedenbeck-Mark-E" }, { "family_name": "Xu", "given_name": "Z. G.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Romeo", "given_name": "O.", "orcid": "0000-0002-4559-2199" }, { "family_name": "Vourlidas", "given_name": "A.", "orcid": "0000-0002-8164-5948" }, { "family_name": "Bale", "given_name": "S. D.", "orcid": "0000-0002-1989-3596" }, { "family_name": "Pulupa", "given_name": "M.", "orcid": "0000-0002-1573-7457" }, { "family_name": "Kasper", "given_name": "J. C.", "orcid": "0000-0002-7077-930X" }, { "family_name": "Larson", "given_name": "D. E.", "orcid": "0000-0001-5030-6030" }, { "family_name": "Livi", "given_name": "R.", "orcid": "0000-0002-0396-0547" }, { "family_name": "Whittlesey", "given_name": "P.", "orcid": "0000-0002-7287-5098" } ], "abstract": "
\n

On 2022 September 5, Parker Solar Probe (Parker) observed a large solar energetic particle (SEP) event at the unprecedented distance of only 15 RS from the Sun. The observations from the Integrated Science Investigation of the Sun (IS\u2299IS) obtained over the course of this event are remarkably rich, and an overview is presented here. IS\u2299IS is capable of measuring ions from 20 keV to over 100 MeV nuc−1 and electrons from 30 keV to 6 MeV; here, we primarily focus on the proton and helium measurements above 80 keV. Among the surprising results are evidence of inverse velocity dispersion at energies above 1 MeV during the onset of the event, a sharp decrease in the energetic particle intensities at all energies at the interplanetary shock crossing, and repeated short durations of highly anisotropic sunward flow. Many changes in the SEP intensities, anisotropy, and spectral steepness are coincident with solar wind structure boundaries identified using the Parker solar wind magnetic field and plasma data. However, there are significant changes that are not correlated with any clearly visible solar wind variation. The observations presented here serve as an introduction to a complex event with numerous opportunities for future, more in-depth studies.

\n
", "doi": "10.3847/1538-4357/ad37f8", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2024-05-10", "series_number": "2", "volume": "966", "issue": "2", "pages": "148" }, { "id": "authors:kxph2-e6861", "collection": "authors", "collection_id": "kxph2-e6861", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230209-988069100.7", "type": "article", "title": "The first gradual solar energetic particle event with an enhanced \u00b3He abundance on Solar Orbiter", "author": [ { "family_name": "Bucik", "given_name": "R.", "orcid": "0000-0001-7381-6949", "clpid": "Bucik-Radoslav" }, { "family_name": "Mason", "given_name": "G. M.", "orcid": "0000-0003-2169-9618", "clpid": "Mason-Glenn-M" }, { "family_name": "G\u00f3mez-Herrero", "given_name": "R.", "orcid": "0000-0002-5705-9236", "clpid": "G\u00f3mez-Herrero-Ra\u00fal" }, { "family_name": "Krupar", "given_name": "V.", "orcid": "0000-0001-6185-3945", "clpid": "Krupar-Vratislav" }, { "family_name": "Lario", "given_name": "D.", "orcid": "0000-0002-3176-8704", "clpid": "Lario-David" }, { "family_name": "Starkey", "given_name": "M. J.", "orcid": "0000-0001-7514-6571", "clpid": "Starkey-Michael-J" }, { "family_name": "Ho", "given_name": "G. C.", "orcid": "0000-0003-1093-2066", "clpid": "Ho-George-C" }, { "family_name": "Rodr\u00edguez-Pacheco", "given_name": "J.", "orcid": "0000-0002-4240-1115", "clpid": "Rodr\u00edguez-Pacheco-Javier" }, { "family_name": "Wimmer-Schweingruber", "given_name": "R. F.", "orcid": "0000-0002-7388-173X", "clpid": "Wimmer-Schweingruber-Robert-F" }, { "family_name": "Espinosa Lara", "given_name": "F.", "orcid": "0000-0001-9039-8822", "clpid": "Espinosa-Lara-Francisco" }, { "family_name": "Tadesse", "given_name": "T.", "clpid": "Tadesse-T" }, { "family_name": "Balmaceda", "given_name": "L.", "orcid": "0000-0003-1162-5498", "clpid": "Balmaceda-Laura-A" }, { "family_name": "Cohen", "given_name": "C. M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-Christina-M-S" }, { "family_name": "Dayeh", "given_name": "M. A.", "orcid": "0000-0001-9323-1200", "clpid": "Dayeh-Maher-A" }, { "family_name": "Desai", "given_name": "M. I.", "orcid": "0000-0002-7318-6008", "clpid": "Desai-Mihir-I" }, { "family_name": "K\u00fchl", "given_name": "P.", "orcid": "0000-0002-3758-9272", "clpid": "K\u00fchl-Patrick" }, { "family_name": "Nitta", "given_name": "N. V.", "orcid": "0000-0001-6119-0221", "clpid": "Nitta-Nariaki-V" }, { "family_name": "Wiedenbeck", "given_name": "M. E.", "orcid": "0000-0002-2825-3128", "clpid": "Wiedenbeck-Mark-E" }, { "family_name": "Xu", "given_name": "Z. G.", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" } ], "abstract": "The origin of \u00b3He bundance enhancements in gradual solar energetic particle (SEP) events remains largely unexplained. Two mechanisms have been suggested: the reacceleration of remnant flare material by coronal mass ejection (CME)-driven shocks in interplanetary space, and concomitant activity in the corona. We explore the first gradual SEP event with enhanced 3He abundance that was observed by Solar Orbiter. The event started on 2020 November 24 and was associated with a relatively fast halo CME. During the event, the spacecraft was at 0.9 au from the Sun. The event-averaged \u00b3He/\u2074He abundance ratio is 24 times higher than the coronal or solar wind value, and the timing of the \u00b3He intensity was similar to that of other species. We inspected available imaging, radio observations, and the spacecraft magnetic connection to the CME source. The most probable cause of the enhanced \u00b3He ions remaining from a preceding long period of 3He-rich SEPs on 2020 November 17\u201323.", "doi": "10.1051/0004-6361/202245037", "issn": "0004-6361", "publisher": "EDP Sciences", "publication": "Astronomy and Astrophysics", "publication_date": "2023-01", "volume": "669", "pages": "Art. No. A13" }, { "id": "authors:p3qyq-abz53", "collection": "authors", "collection_id": "p3qyq-abz53", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220127-677276900", "type": "conference_item", "title": "Multi-spacecraft Observations of Gradual Solar Energetic Particle Events with Enhanced \u00b3He Abundance", "author": [ { "family_name": "Bucik", "given_name": "Radoslav", "orcid": "0000-0001-7381-6949", "clpid": "Bucik-Radoslav" }, { "family_name": "Mason", "given_name": "Glenn M.", "orcid": "0000-0003-2169-9618", "clpid": "Mason-Glenn-M" }, { "family_name": "G\u00f3mez-Herrero", "given_name": "Ra\u00fal", "clpid": "G\u00f3mez-Herrero-Ra\u00fal" }, { "family_name": "Dayeh", "given_name": "Maher A.", "clpid": "Dayeh-Maher-A" }, { "family_name": "Desai", "given_name": "Mihir I.", "orcid": "0000-0002-7318-6008", "clpid": "Desai-Mihir-I" }, { "family_name": "Cohen", "given_name": "Christina M. S.", "orcid": "0000-0002-0978-8127", "clpid": "Cohen-Christina-M-S" }, { "family_name": "Lario", "given_name": "David", "orcid": "0000-0002-3176-8704", "clpid": "Lario-David" }, { "family_name": "Balmaceda", "given_name": "Laura A.", "orcid": "0000-0003-1162-5498", "clpid": "Balmaceda-Laura-A" }, { "family_name": "Krupar", "given_name": "Vratislav", "orcid": "0000-0001-6185-3945", "clpid": "Krupar-Vratislav" }, { "family_name": "Wiedenbeck", "given_name": "Mark E.", "orcid": "0000-0002-2825-3128", "clpid": "Wiedenbeck-Mark-E" }, { "family_name": "Wimmer-Schweingruber", "given_name": "Robert F.", "orcid": "0000-0002-7388-173X", "clpid": "Wimmer-Schweingruber-Robert-F" }, { "family_name": "Ho", "given_name": "George C.", "orcid": "0000-0003-1093-2066", "clpid": "Ho-George-C" }, { "family_name": "Rodriguez-Pacheco", "given_name": "Javier", "clpid": "Rodriguez-Pacheco-Javier" }, { "family_name": "Nitta", "given_name": "Nariaki V.", "clpid": "Nitta-Nariaki-V" }, { "family_name": "K\u00fchl", "given_name": "Patrick", "clpid": "K\u00fchl-Patrick" }, { "family_name": "Xu", "given_name": "Zigong", "orcid": "0000-0002-9246-996X", "clpid": "Xu-Zigong" }, { "family_name": "Asfaw", "given_name": "Tilaye T.", "clpid": "Asfaw-Tilaye-T" } ], "abstract": "Flare suprathermal ions with enhanced \u00b3He and heavy-ion abundances are an essential component of the seed population accelerated by CME-driven shocks in gradual solar energetic particle (GSEP) events. However, the mechanisms through which CME-driven shocks gain access to flare suprathermals and produce spectral and abundance variations in GSEP events remain largely unexplored. We report two recent GSEP events: one observed by Solar Orbiter on 2020 Nov 24 (the first GSEP event on Solar Orbiter) and the other by ACE on 2021 May 29 (the most intense GOES proton event in the present solar cycle). The events were preceded by impulsive SEP (ISEP) events. Abundances and energy spectra are markedly different in the examined events at < 1 MeV/nucleon. For example, in the May event, Fe/O is typical of ISEP events, a factor of 100 to 10 higher than Fe/O in the November event. \u00b3He abundance in the November event is high, typical of ISEP events, while in the May event, it is much lower, though finite. The May event shows a hard \u2074He spectrum with a power-law index of \u22121.6, and the November event a soft spectrum with an index of \u22123.5. The events were associated with halo CMEs with speeds around 900 km/s. The November event was also measured by Parker Solar Probe and the May event by STEREO-A and Solar Orbiter. This paper discusses the origin of vastly different abundances and spectral shapes in terms of variable remnant population from preceding ISEP events. Furthermore, we discuss a possible direct contribution from parent flares.", "doi": "10.1002/essoar.10509271.2", "publisher": "Wiley", "publication_date": "2021-12-30" } ]