The dynamics of suprathermal and energetic particles in the heliosphere encompass various processes, from the acceleration of solar wind electrons/ions to solar energetic particle events related to solar eruptive phenomena. Despite decades of research, several aspects of suprathermal and energetic particle production remain unknown, with the main candidate production mechanisms being magnetic reconnection, collisionless shocks and several categories of wave-particle interactions. How suprathermal and energetic particles are transported through the heliosphere is also object of active debate, and largely unconstrained. Recent missions, such as Solar Orbiter and Parker Solar Probe, have delivered excellent observations from the inner heliosphere, both remotely and in situ. When combined with data from missions like ACE, SOHO, Wind, and STEREO at 1 AU, these observations across varying radial distances offer an unprecedented opportunity to characterize the sources and transport mechanisms of suprathermal and energetic particles in the heliosphere.
This session invites contributions that explore space-borne and ground-based observations, as well as theoretical and modelling approaches, to deepen our understanding of the acceleration and transport of suprathermal and energetic particles in the heliosphere. We encourage submissions that provide new insights, propose innovative methodologies, or synthesize data across multiple missions to address these critical scientific challenges.
Orals: Wed, 6 May, 16:15–18:00 | Room 0.15
The composition of solar energetic particle (SEP) events varies significantly from event to event and with energy within individual events. For example, although the ‘typical’ Fe/O ratio is considered to be 0.134, it is observed to vary from <0.01 to >1 and often shows strong dependence on energy. Several processes and conditions may contribute to this variability, including the dominant acceleration process (e.g., diffusive shock acceleration versus magnetic reconnection), the properties of the seed population being accelerated, the conditions of the interplanetary medium as the particles travel from the acceleration region to the observer. Here we examine the composition variability as measured by older missions such as ACE and STEREO, but also include more recent observations from Parker Solar Probe, Solar Orbiter and the newly launch Interstellar Mapping and Acceleration Probe (IMAP). The combination of these measurements also provides the capability of examining the composition of individual events as a function of radius and longitude.
How to cite: Cohen, C.: Composition variations and their implications for SEP acceleration and transport processes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5099, https://doi.org/10.5194/egusphere-egu26-5099, 2026.
The Chinese Tianwen1 mission arrived at Mars since 2021 and the Mars Energetic Particle Analyzer (MEPA) instrument has been monitoring the energetic particle fluxes at the orbit of Mars, measuring protons in the energy range up to 100 MeV. It has captured a series of Solar Energetic Particle (SEP) events at Mars and we have anlayzed the energy spectra and time evolution and each event and derived their statistical properties which show different characteristics from SEP events detected elsewhere. We will give a brief summary of the MEPA observed SEP events at Mars in comparison to other events observed at Earth and other locations.
How to cite: Guo, J. and Cao, Y.: SEP events observed at Mars by the Chinese Tianwen1 mission over the past years, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2738, https://doi.org/10.5194/egusphere-egu26-2738, 2026.
On 21 November 2024, a strong solar energetic particle (SEP) event implying protons of 100 MeV near Earth was associated with an eruption located on the far side of the Sun as viewed from Earth.
The source region was identified using EUV observations from the Solar-Terrestrial Relations Observatory (STEREO) as NOAA AR 13892, located around (lon, lat) = (355°, -20°) in Carrington coordinates at around 00:45 UT. Due to its location, the associated flare produced only weak soft X-ray signatures in Earth-based observations. The Spectrometer/Telescope for Imaging X-rays (STIX) instrument on-board Solar Orbiter, which was also positioned on the far side relative to the parent active region, recorded an increase in the 15-25 keV range.
The flare was followed by a coronal mass ejection (CME) of speed 1436 km/s, propagating on the solar limb and driving a shock wave at its front. The 3D geometry of the CME-driven shock was reconstructed using white-light remote-sensing observations from STEREO-A and SOHO. This was then combined with global magneto-hydrodynamic (MHD) simulations from Predictive Science Inc. (PSI), to derive the MHD properties of the shock surface, as well as the magnetic field lines connecting the spacecraft to the Sun’s surface.
This enables the study of MHD shock parameters evolution along field lines regarding the SEP profile and characteristics measured at the corresponding spacecraft. We therefore investigated acceleration scenarios for the energetic particles that reached Earth, STEREO-A and Solar Orbiter, which are magnetically connected to different regions of the evolving shock.
How to cite: Jarry, M., Papaioannou, A., Talebpour Sheshvan, N., Rouillard, A. P., Lavasa, E., Vasalos, G., and Anastasiadis, A.: Proton acceleration by CME-driven shock during the 21 November 2024 (GLE76) event, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19845, https://doi.org/10.5194/egusphere-egu26-19845, 2026.
Enhancements in 3He abundance, a characteristic feature of impulsive solar energetic particle events, are also frequently observed in gradual solar energetic particle events, but the origin of the 3He-rich contribution to the seed population (remnant material versus fresh injection from the parent active region) remains unresolved. We investigate the origin of 3He enrichment in high-energy (25–50 MeV) solar proton events observed by the Solar and Heliospheric Observatory, selecting events that coincide with <1 MeV/nuc 3He-rich periods detected by the Advanced Composition Explorer from 1997 to 2021. Extreme-ultraviolet imaging from the Solar Dynamics Observatory and STEREO reveals narrow, jetlike eruptions in the parent active regions of about 60% of the events. Notably, the highest 3He/4He ratios occur when coronal jets are present, consistent with fresh, jet-driven injection of suprathermal 3He that is subsequently reaccelerated during the event. Correspondingly, jet-associated events show fewer pre-event (residual) 3He counts, indicating that enrichment in these cases does not primarily come from remnant material. We find a positive correlation between 3He/4He and Fe/O, strongest in jet-associated events, consistent with a common jet-supplied seed population reaccelerated by the coronal mass ejection shock. We also find that a substantial fraction of apparent 3He enrichments arise from overlap with independent impulsive SEP activity, highlighting the need to separate superpositions from true reacceleration signatures.
How to cite: Bucik, R., Hart, S., Dayeh, M., Desai, M., Mason, G., and Wiedenbeck, M.: Helium-3 Enrichment in Gradual Solar Energetic Particle Events: Evidence for a Jet-supplied Seed Population, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8583, https://doi.org/10.5194/egusphere-egu26-8583, 2026.
The significance of 3He-rich solar energetic particle (SEP) events, though often overlooked, is threefold: (1) they trace small-scale sites that may serve as precursors to larger eruptive activity, (2) they probe the structure of magnetic connectivity that help refine solar wind and coronal magnetic field models, and (3) they provide constraints on waveparticle interactions and turbulence that influence the acceleration of heavy ions. These 3He-rich events are typically short-lived, exhibit low total particle intensity, and are associated with active region jets and Type III radio bursts. This study presents results from a 3He/4He ratio survey using Parker Solar Probe’s IS⊙IS/EPI-Hi instrument from its launch through 2025. We investigate the occurrence, energy spectra, and spatial distribution of 3He-rich SEP events across radial distances. By analyzing the radial distribution of 3He-rich events, we aim to determine whether their characteristic enhancements persist over heliocentric distance or degrade due to transport effects, complementing prior studies focused primarily on longitudinal connectivity. Emphasis is placed on identifying correlations between 3He enrichment and solar source properties, including the differential emission measure (DEM) of active regions and the presence of jets. DEM maps constrain low coronal temperature and density structure, enabling identification of plasma environments where ion cyclotron waves may resonate with ions of specific charge-to-mass ratios, such as the case in which 3He is selectively energized, thus linking in-situ 3He-rich SEP composition via wave-particle processes. We further compare PSP observations with those from other spacecraft (IMAP, ACE, STEREO, Solar Orbiter) during periods of apparent Parker spiral field line alignment to study transport and re-acceleration effects.
How to cite: Muro, G., Cohen, C., Leske, R., and Xu, Z.: 3He-Rich SEPs throughout the inner heliosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8158, https://doi.org/10.5194/egusphere-egu26-8158, 2026.
We investigate two adjacent solar energetic electron (SEE) events measured by Solar Orbiter/EPD at 0.93 au with a separation of ~30 minutes on December 24, 2022. STEREO-A (Wind) with a longitudinal separation of ~5°(19°) from Solar Orbiter shows no clear observations of SEEs, indicating the presence of a <20° longitudinal distribution for these two events. In addition, the nearly symmetric peaks in temporal profiles and strongly beamed pitch angle distributions in both events suggest that most of these SEEs undergo essentially scatter-free propagation in the interplanetary medium. Utilizing the pan-spectrum fitting method, we self-consistently determine the spectral shape of background-subtracted electron peak flux vs energy. Event #1 is fitted to a triple power-law spectrum with two spectral breaks at ~22 and 290 keV. Event #2 shows a double power-law spectrum with a spectral break around 25 keV. For both events, the power-law spectrum extends down to below 10 keV, implying that these SEEs could originate high in the corona. We further derive the electron injection profiles at sun by forward fitting in-situ temporal profiles, for the two events. According to the characteristics of injection timing and spectral shape, Event #1 consists of three SEE populations, respectively, at energies below ~22 keV, between ~22 keV and ~290 keV, and above ~290 keV, while Event #2 consists of two populations, respectively, at energies below and above ~25 keV. The low-energy population likely provides seed populations for further acceleration process (processes) to form the high-energy population (populations).
How to cite: Wang, L., Li, Y., Wimmer-Schweingruber, R., Su, Y., and Krucker, S.: Solar Energetic Electron Events on 2022 December 24, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1917, https://doi.org/10.5194/egusphere-egu26-1917, 2026.
With its inclined orbit, Solar Orbiter now reaches higher heliocentric latitudes than are accessible from the ecliptic. We will investigate small, dispersive solar particle events and compare their onset times with X-ray measurements. Using the first particles to arrive, we determine the path lengths along which they traveled and compare these with the expected values. This exploratory work could help elucidate the global configuration of the coronal and interplanetary magnetic field and discern between traditional models and, e.g., the Fisk model. We find that at the heliographic latitudes attained by Solar Orbiter, small, dispersve events do not appear different form in-ecliptic solar particle events.
How to cite: Wimmer-Schweingruber, R. F., Rodriguez-Pacheco, J., Ho, G. C., Warmuth, A., Berger, L., Mason, G. M., Ding, Z., Gomez-Herrero, R., Krucker, S., Kollhoff, A., Espinosa, F., Kühl, P., Allen, R. C., Cernuda, I., Gunaseelan, S., Jentsch, E., Kartavykh, Y., Fleth, S., and Eldrum, S.: Dispersive out-of-ecliptic solar particle events observed by EPD on Solar Orbiter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6620, https://doi.org/10.5194/egusphere-egu26-6620, 2026.
Solar energetic particles (SEPs), which originate from the eruptive activities of the solar corona, are accompanied by a significant amount of high-energy charged particles, can cause damage to spacecraft systems and affect human activities in space.
Describing the propagation of SEPs in interplanetary space constitutes an indispensable component in the construction of SEP physical model. In this work, we developed a coupled Physics-based model composed of a data-driven analytical background model and a particle transport model represented by the focused transport equation (FTE). By using the coupled model, we try to simulate the energetic particle propagation in different interplanetary structures, such as the stream interaction region (SIR) and the coronal mass ejection (CME), with specific cases observed by WIND, STEREO A/B and SOHO, and to explore the physical nature behind the spacecraft observations.
How to cite: Shen, F., Tao, X., Luo, X., and Feng, X.: Modelling Solar Energetic particle (SEP) Transport Related with Stream Interaction Regions and CME Events, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4592, https://doi.org/10.5194/egusphere-egu26-4592, 2026.
A significant fraction of the energy of extreme solar eruptive events is channeled into the energetic particles associated with gradual solar energetic particle (SEP) events, posing a significant radiation hazard to humans and technological assets in space. The high-energy particles in gradual SEP events are known to be accelerated by coronal-mass-ejection-driven shocks, but how the resulting SEP energy spectra for different elements depend on the fundamental parameters that characterize the shock and ambient upstream medium remains an open question. Here we present the predicted properties of SEP energy spectra using a Liouville mapping technique applied to the electromagnetic field structure of the shock transition generated by a suite of hybrid kinetic ion and fluid electron simulations of quasiperpendicular shocks. We focus on how the predicted SEP energy spectra depend on the Mach number and shock-normal angle of a collisionless shock in the planar limit and on the suprathermal velocity distributions of protons and heavier elements in the upstream interplanetary medium. For example, we find accelerated SEP energy spectra peak at higher energies for higher shock-normal angles, in qualitative agreement with previous numerical and observational findings. We summarize our findings with a comparison of the fundamental parameter dependencies revealed here to those found in observations of CME shocks in the inner heliosphere.
How to cite: Howes, G., Lnu, Y., Felix, A., and Riggs, J. D.: Dependence of Solar Energetic Particle Energy Spectra on the Fundamental Parameters of CME Shocks., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22688, https://doi.org/10.5194/egusphere-egu26-22688, 2026.
The spatial size of collisionless shock waves is suggested to play an important role in determining the maximum energy gain of particles accelerated at heliospheric and astrophysical shocks. In addition, shocks energize particles with different starting/upstream energies differently. This study aims to investigate the maximum energy gain at heliospheric shocks at various sizes and seed conditions. In our comparison, we focus on the Martian, Venusian, terrestrial, and Jovian bow shocks, as well as interplanetary shocks, using spacecraft data from the MAVEN, Venus Express, Magnetospheric Multi-Scale (MMS), Juno, Parker Solar Probe, and Solar Orbiter spacecraft missions, respectively. These shock systems are chosen because of their vast physical size difference and therefore constitute perfect laboratories for the intended comparison study. We explore the maximum energy dependence on the shock obliquity and shock Mach number measured for each shock crossing. In addition to the maximum energy, we also compare the suprathermal electron spectral index for the different sets of shocks and its dependence on the shock obliquity.
How to cite: Lindberg, M., Hietala, H., Koller, F., and Vuorinen, L.: Comparison of Particle Acceleration at Planetary Bow Shocks and Interplanetary Shocks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5421, https://doi.org/10.5194/egusphere-egu26-5421, 2026.
The joint ESA/NASA Solar Orbiter mission has observed suprathermal and energetic particles throughout much of Solar Cycle 25, spanning the period from 2020 to 2025, providing unprecedented coverage of the inner heliosphere. Measurements of protons, and heavy ions show substantial temporal variability in particle intensities over the solar cycle. In particular, the Suprathermal Ion Spectrograph (SIS) of the Solar Orbiter Energetic Particle Detector (EPD) measures suprathermal ion abundances from hydrogen through iron with high precision. Previous studies have shown that the suprathermal ion population in the heliosphere arises from multiple source populations. In this work, we focus on the composition and origin of the quiet-time suprathermal population, using Solar Orbiter/SIS composition measurements to examine how source contributions vary with solar activity level and heliocentric distance. We find that during periods of low solar activity and relatively stable particle intensities, the suprathermal heavy-ion composition closely resembles that of the ambient solar wind and/or corotating interaction regions, indicating that these sources make a dominant contribution under quiet conditions. Impulsive material, such as 3He-rich ions, becomes more prominent during more active intervals but represents a reduced fraction of the suprathermal pool during quiet times. These observations demonstrate that the quiet-time suprathermal population in the inner heliosphere is largely controlled by solar-related sources, providing important constraints on the seed population available for subsequent energetic particle acceleration.
How to cite: Ho, G., Mason, G., Allen, R., Hart, S., Kouloumvakos, A., Wimmer-Schweingruber, R., Rodríguez-Pacheco, J., and Gómez-Herrero, R.: Quiet-time Suprathermal Intensities and Composition Observed by Solar Orbiter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5904, https://doi.org/10.5194/egusphere-egu26-5904, 2026.
How to cite: Han, C., Wimmer-Schweingruber, R., Kühl, P., Berger, L., Ding, Z., Kollhoff, A., Shi, Q., Xu, Z., and Qin, M.: Modulation of the Heliospheric Current Sheet in the Propagation of Solar Energetic Electrons: an Investigation Based on CoSEE-Cat, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6684, https://doi.org/10.5194/egusphere-egu26-6684, 2026.
We investigate the transport of solar energetic particles (SEPs) during the relativistic and longitudinally widespread event of 28 October 2021 - GLE73, with the aim of quantifying the roles of parallel and perpendicular diffusion and constraining the spatial extent of the injection region. Inverse modeling is performed using numerical simulations of focused particle transport that include cross-field diffusion, in order to reproduce multi-spacecraft observations from STEREO-A, Solar Orbiter, and near-Earth missions over a wide range of electron and proton energies. Simulated intensity and anisotropy time profiles are compared across multiple helio-longitudes to derive consistent transport parameters. The results yield parallel mean free paths compatible with predictions from dynamical turbulence models for pitch-angle scattering. The inferred perpendicular mean free paths constitute a significant fraction of the parallel values, amounting to approximately 1–3% for electrons and 5–10% for protons, with a tendency to increase with particle rigidity. The injection region is found to be relatively narrow (≤20°) and to decrease with increasing rigidity. These findings indicate that a localized injection combined with efficient perpendicular diffusion can account for the observed widespread SEP signatures.
Acknowledgement
This research was supported by the European Union’s Horizon Europe programme under grant agreement No. 101135044 (SPEARHEAD; https://spearhead-he.eu/).
How to cite: Lavasa, E., Lang, J. T., Papaioannou, A., Strauss, D. T., Mallios, S., Hillaris, A., Kouloumvakos, A., Anastasiadis, A., and Daglis, I. A.: Transport of relativistic solar energetic particles during GLE73, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20416, https://doi.org/10.5194/egusphere-egu26-20416, 2026.
It is well established that solar energetic particles events typically show normal velocity dispersion (VD), where the release of particles is independent of energy, producing anpattern with an earlier onset at higher energies. Recent measurements by NASA’s Parker Solar Probe (PSP) and ESA’s Solar Orbiter(SolO), however, reveal events with a mixed dispersion behaviour: VD at lower energies, but an inverse velocity dispersion (IVD) at higher energies, in which higher-energy particles arrive later than lower-energy ones. Building on our earlier SolOsurvey of 10 IVD proton events and its interpretation in terms of time-dependent shock diffusive acceleration, we extend the method to multi-point IVD observations by SolO, STEREO-A (STA), and PSP. For events observed at multiple longitudes, we apply consistent VDA/IVD fitting to infer release heights and radial mean free paths at each spacecraft and quantify their variability with magnetic connection. Observers with larger connection angles systematically show delayed VDA release times; we compare these delays with EUV-wave arrival at the magnetic footpoint or with fitted CME connection times. We further investigate inter-spacecraft SEP properties, such as time-integrated spectra, spectral breaks, and pitch-angle anisotropies.
How to cite: Li, Y., Guo, J., Pacheco, D., Ding, Z., Temmer, M., and Wimmer-Schweingruber, R. F.: Inverse velocity dispersion events in multi-spacecraft analyses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20100, https://doi.org/10.5194/egusphere-egu26-20100, 2026.
Impulsive solar energetic particle (SEP) events are characterized by compositional anomalies, the highly elevated 3He/4He ratio in particular. They also tend to be abundant in heavy elements and electrons. It is still not clear how impulsive SEP (ISEP) events are produced, largely because of the difficulty of finding their solar sources. It is true that they are often identified as coronal jets, energetically much less pronounced than solar flares, which are found around the times of type III radio bursts in the decametric-hectometric wavelength range. But in a small number of ISEPs observed by Solar Orbiter, search of the solar source seems to be not hopeful. In this work we try to find the solar sources of the ISEPs with high 3He flux as published by Kouloumvakos et al. (2025). We first concentrate on those events that occurred while Solar Orbiter was magnetically connected to the part of the Sun visible from Earth so that we can make use of multi-channel SDO/AIA data. To explore the effect of spatial resolution on the detectability of the source region, we study ISEPs that were observed when Solar Orbiter was close to the Sun and the likely source regions happened to be in the field of view of EUI/HRI. Lastly we investigate the relation of dropouts in ions and electrons with the properties of the source regions.
How to cite: Nitta, N., Bucik, R., Mason, G., Ho, G., Rodríguez-Pacheco, J., Wimmer-Schweingruber, R., Allen, R., Kouloumvakos, A., Gomez-Herrero, R., and Krupar, V.: Solar sources of impulsive solar energetic particle events with high 3He content , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16510, https://doi.org/10.5194/egusphere-egu26-16510, 2026.
We present observations of impulsive solar energetic particle events on 2025 March 20 observed at high heliolatitude by Solar Orbiter and compare them with near-ecliptic observations by the Wind spacecraft. Solar Orbiter, located at 0.38 au, a Carrington longitude of 139.7◦ and a latitude of −16.6◦, detected two ion events at ∼0.1-6 MeV and two electron events at ∼40-200 keV. These events exhibit clear velocity dispersion and strong field-aligned anisotropy. Velocity dispersion analysis of both ion and electron events yields path lengths consistent with the nominal Parker spiral length. Furthermore, the first electron event exhibits a double-power-law spectrum with an index of 2.3 ± 0.3 below a break energy of 58 ± 4 keV and an index of 4.0±0.2 at energies above, while the second electron event exhibits a single-power-law spectrum with an index of 4.6 ± 0.2. In contrast, the Wind spacecraft, located at 1 au, a Carrington longitude of 120.0◦, and a latitude of −7.1◦, observed only one electron event, which shows insignificant velocity dispersion and arrives ∼20 min later than expected. The Parker spiral footpoints of the two spacecraft were separated by ∼15◦ in longitude and ∼10◦ in latitude, providing a lower limit on the angular extent of impulsive electron events. The delayed arrival at Wind may be attributed to the electron diffusion in the solar source region.
How to cite: Yang, L., Ding, Z., Wang, W., Heidrich-Meisner, V., Wimmer-Schweingruber, R., Wang, L., Pisa, D., Zhu, Y., Battaglia, A., Kollhoff, A., Rodríguez-Pacheco, J., and Ho, G.: Impulsive Solar Energetic Particle Events at High Heliolatitude, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8925, https://doi.org/10.5194/egusphere-egu26-8925, 2026.
On 9 October 2024, a major Solar Energetic Particle (SEP) event was detected simultaneously across a wide range of heliolongitudes and heliocentric distances. Signatures were observed by Solar Orbiter, Parker Solar Probe (PSP), STEREO-A, near-Earth spacecraft (SOHO, GOES, ACE), and surface instruments on Mars (MSL/RAD). The event originated from an X1.8 solar flare in Active Region (AR) 3848, which produced a fast, Earth-directed full-halo coronal mass ejection (CME). This study aims to characterize the acceleration and heliospheric distribution of SEPs during this event and to evaluate its implications for space weather forecasting and radiation risks for future human exploration of Mars. We combined imaging and in situ particle observations from multiple spacecraft positioned at different longitudes and heliocentric distances. Analyses included flare and CME timing, SEP fluxes, onset times, and energy spectra at each vantage point. Multi-point comparisons allowed us to assess how CME-driven shocks accelerate and transport SEPs, and how cross-field propagation and interplanetary scattering shaped the observed particle distributions, particularly at Mars.
The X1.8 flare began at 01:25 UTC, peaked at 01:56 UTC, and ended at 02:43 UTC. The associated full-halo CME was first detected by LASCO at 02:12 UTC from ~N13 W08, with speeds estimated at ~1,500 km/s (leading edge) and ~2,100 km/s (shock front). The CME arrived at Earth around 10 October 14:45 UTC. Solar proton intensities began rising at 02:40 UTC and reached S2 (moderate) radiation storm levels by 07:30 UTC. Widespread SEP detections, including at Mars, demonstrate efficient particle acceleration over an exceptionally broad spatial domain and highlight the role of extended shock fronts, cross-field diffusion, and interplanetary turbulence in shaping SEP propagation. These results provide critical constraints for SEP transport models and underline the value of multi-point observations for advancing forecasting capabilities and mitigating radiation hazards in deep space missions.
How to cite: Khaksari, S., Wimmer-Schweingruber, R. F., Löwe, J. L., Guo, J., Pacheco, D., Heber, B., Dröge, H., J. Lillis, R., Ding, Z., Ehresmann, B., M. Hassler, D., Löffler, S., Zeitlin, C., and Matthiä, D.: Requirements for Solar Energetic Particle Forecasting at Mars: Lessons from Multi-Point Observations of the 9 October 2024 CME-Driven Shock, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10464, https://doi.org/10.5194/egusphere-egu26-10464, 2026.
Radiation environments driven by solar energetic particle (SEP) events are a key risk for deep-space missions, and robust flux retrievals are essential for both operations and long-term environment models. We present an end-to-end proton flux inversion pipeline for the Radiation-Hard Electron Monitor (RADEM) on ESA’s JUICE mission, focusing on the proton detector channels in the nominal configuration. We apply a normalization that converts Geant4 simulation counts into calibrated response-matrix elements, consistent with the General Particle Source (GPS) setup (surface source on a sphere) and a cosine-weighted angular distribution within a finite cone. The response matrix is then used with multiple inversion approaches and time-averaging schemes to retrieve proton intensities in predefined energy bands.
To validate absolute scaling and spectral behavior, we compare RADEM-derived proton time series for selected SEP events with contemporaneous IREM (INTEGRAL Radiation Environment Monitor) Level-2 proton differential fluxes integrated over matching energy bands. The comparison includes quiet-time intervals before and after each event and focuses on periods when JUICE and IREM were in close spatial proximity. We discuss practical sensitivities across the tested inversion approaches and outline next steps. This work provides a reproducible foundation for SEP analyses with RADEM and supports broader heliospheric energetic particle studies across missions.
How to cite: Kilic, C., Galli, A., Hajdas, W., Grzanka, L., Adamus, G., Kozimor, D., and Swakoń, J.: Deriving SEP Proton Fluxes with the JUICE Radiation Environment Monitor: Response-Matrix Inversion and Near-Conjunction Validation with IREM, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19322, https://doi.org/10.5194/egusphere-egu26-19322, 2026.
The HENON CubeSat mission is designed to fly on a distant retrograde orbit (DRO) around the Earth at about 0.1 Earth radii, for advance time space weather monitoring. The mission has a set of instruments which include an energetic particle detector measuring protons from a few MeV to hundreds of MeV. In this work, we investigate under what conditions energetic particles can be accelerated at interplanetary shocks above the detection threshold of about 2 MeV of the HENON instrument.
We set up a test particle numerical simulation in which protons move in the drift approximation around a shock transition, and are accelerated each time they cross the shock. Protons are injected at the shock with an energy of few tens of keV and are scattered in pitch angle by a collision operator. In the simulation, we vary the pitch-angle scattering time, the shock compression ratio, and the type of transport, which can be either normal diffusion or superdiffusion. In the superdiffusive case, a power-law distribution of scattering times is generated in order to reproduce a Levy walk. The proton energy spectra are obtained as a function of the elapsed time, keeping in mind that for strong heliospheric shocks associated to fast coronal mass ejections, the shock lifetime is of the order of one or two days. Several runs are carried out in order to determine (i) the parameter domain which leads to efficient acceleration and (ii) which runs lead to the highest energies. For typical parameters, superdiffusive acceleration turns out to be faster in accelerating protons. Simulation results will be presented for a wide parameter range, and we find that energies in the range of 2-10 MeV can be reached in a number of cases.
This work was funded by the Italian Space Agency (ASI) through the Argotec contracts, numbers ARG-IT-CON-P-HEN-220002 and ARG-IT-CON-P-HEN-250003. GZ, SP, and GP acknowledge partial support by the Italian PRIN 2022, project 2022294WNB entitled "Heliospheric shocks and space weather: from multispacecraft observations to numerical modelling” (CUP H53D23000900006).
How to cite: Zimbardo, G., Scarivaglione, L., Prete, G., Perri, S., Marcucci, M. F., Laurenza, M., Landi, S., Greco, A., Malara, F., and Servidio, S.: Numerical study of proton acceleration at interplanetary shocks for the interpretation of the HENON CubeSat mission measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12945, https://doi.org/10.5194/egusphere-egu26-12945, 2026.
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 March 23, 2024, the successive eruption of two magnetic flux ropes (MFRs) 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 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 proton 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 more close to the abundance of the flare-related particles, suggesting the remnant particles of flare confined in the IIS.
How to cite: Chen, X., Li, C., Xu, Z., Nicolaou, G., Kollhoff, A., Ho, G. C., Wimmer-Schweingruber, R. F., and Owen, C. J.: Local Particle Acceleration in an ICME-in-Sheath Structure Observed by Solar Orbiter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4238, https://doi.org/10.5194/egusphere-egu26-4238, 2026.
We investigate the impact of a Coronal Mass Ejection (CME) on the transport and acceleration of relativistic protons in the solar wind using a coupled 3D Magnetohydrodynamics (MHD) simulation and test-particle approach. The CME is modelled as a spheromak propagating through a Parker-like solar wind and the trajectories of 5 GeV protons are integrated in the guiding-centre approximation limit. Our results show that the CME can significantly accelerate the protons up to tens of GeV.
Particles gain energy through an adiabatic heating mechanism as they access to regions of compressed plasma downstream of the CME-driven shock. In our configuration, the maximum energy gain, which is about 50 % per crossing, occurs when the perturbation reaches about 0.3 AU, which corresponds to ~9 hours after the spheromak is injected.
The parallel diffusion plays an important role by confining the particles within the simulation domain long enough for them to encounter the disturbance multiple times and gain energy at each interaction. Particles' energy spectra at 1 AU shows the energy gain depends on the longitude of the magnetic field line on which the particle is located. They also show that the spectra are harder for smaller values of the parallel mean free path λ.
How to cite: Houeibib, A., Pantellini, F., and Griton, L.: Acceleration of relativistic protons in a CME-perturbed solar wind, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19733, https://doi.org/10.5194/egusphere-egu26-19733, 2026.
Solar energetic particle (SEP) events provide key constraints on particle acceleration and transport in the heliosphere. While most events are dominated by outward streaming particles along open magnetic field lines, rare bidirectional events showing concurrent sunward and anti-sunward flows, offer a unique probe of magnetic connectivity and the coupling of multiple acceleration sources. Here we analyze two uncommon bidirectional anisotropic SEP events observed by Solar Orbiter, focusing on their association with magnetic flux ropes. Both events exhibit two distinct velocity-dispersion signatures during the onset phase, accompanied by opposite anisotropies. The sunward-streaming protons show a delayed apparent release, a harder spectrum, and higher intensities, consistent with acceleration at a CME-driven shock and subsequent transport within transient magnetic structures. In contrast, the promptly released anti-sunward protons are more consistent with flare-related acceleration. These observations demonstrate the diagnostic power of jointly using anisotropy, inferred release times, source spectra, and in situ magnetic structure signatures to disentangle SEP transport in complex large-scale transients, and they pose new constraints for current SEP transport models.
How to cite: Ding, Z., Wimmer-Schweingruber, R., Yang, L., Kollhoff, A., Kühl, P., Berger, L., Ho, G., and Mason, G.: The impact of large-scale transient structures on solar energetic particle transport, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9709, https://doi.org/10.5194/egusphere-egu26-9709, 2026.
Macro-modeling of the solar corona and solar wind seeks to describe the physical mechanisms that accelerate plasma particles to supersonic speeds and to explain their properties at various heliographic coordinates, increasingly sampled by space missions. Recent observational evidence provided by Parker Solar Probe on suprathermal electrons with Kappa-type velocity distributions at the origins of the solar wind has revived interest in deciphering kinetic effects and their consequences. We present new results from two complementary approaches of the solar wind, namely the kinetic-exospheric models and the HD/MHD fluid models with kinetic components. In this case, both approaches capture and quantify the effects of suprathermal electrons modeled with Kappa distributions, standard and regularized Kappa models. The latter have been introduced more recently for a physically and statistically consistent characterization of suprathermal populations and their consequences. Overestimations of the energy transferred directly or indirectly (e.g., through the ambipolar field created in the acceleration regions) to the solar wind by suprathermal electrons are thus prevented. One can consider for the first time those more energetic electrons, with strong suprathermal tails and associated with the source of energetic solar outflows, such as coronal mass ejections and bursts. Furthermore, such conditions cannot be ruled out as being conducive to the shaping of stellar winds in the astrospheres of stars with coronas much hotter than those of the solar corona.
How to cite: Lazar, M., Vinogradov, A., Poedts, S., and Fichtner, H.: The impact of suprathermal electrons in solar wind macromodeling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17669, https://doi.org/10.5194/egusphere-egu26-17669, 2026.
