[
{
"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
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
\n
On 2022 September 26, we observed a quiescent solar prominence with Hα imaging spectroscopy using the Solar Dynamics Doppler Imager (SDDI) on board the Solar Magnetic Activity Research Telescope (SMART). Unlike earlier works that detected 4 and 15 minute oscillations through long-slit, 1D wavelet methods, we adapt the wavelet analysis to 3D data to explore the full prominence structure. Complementary data from Solar Dynamics Observatory/Atmospheric Imaging Assembly (304, 171 Å) STEREO-A Extreme Ultraviolet Imager (EUVI; 304 Å), and Solar Orbiter Extreme Ultraviolet Imager/Full Sun Imager (304, 174 Å) enable a multiview, multithermal investigation of wave periodicity across the prominence. Our aim is to characterize how oscillatory periods are distributed in plasma at different temperatures and viewing angles, thereby assessing wave propagation and variability throughout the prominence body. We analyze time series of Doppler signal from SMART/SDDI Hα observations alongside extreme-ultraviolet intensity variations from space-based instruments. We detect oscillatory plasma motions with periods spanning 3–74 minutes. Strong periodicity at 20, 31, and 53 minutes dominates in neutral plasma (Hα), while 13 and 74 minute oscillations are pronounced in the 304 Å passband, concentrated mainly in the central prominence. Additional short-period fluctuations include weaker 3–6 minute oscillations and rapid 30 s transverse waves in Doppler signals near the solar surface. These findings highlight the richness of wave periodicity in quiescent prominences, revealing a dynamic superposition of long- and short-period oscillations and kink-like disturbances. This multi-instrument, 3D perspective advances our understanding of how prominence plasma supports and modulates diverse wave modes.
\n
\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
\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
\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
\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