As Solar Cycle #25 reaches its peak of activity, Solar Orbiter is observing a substantial increase in solar flares, coronal mass ejections (CMEs), and solar energetic particles (SEPs). Specifically, the Energetic Particle Detector (EPD) on board Solar Orbiter has been tracking and characterizing the rise in SEP activity over the past five years. This paper focuses on the intensities of suprathermal and energetic particles from 2020 through 2025. Both electrons, ions, and 3He particles show a notable increase, which aligns closely with other solar phenomena. We compare the SEP flux observed during this cycle with the measurements from Cycles #23 and #24, as recorded by ACE. The results reveal that the flux levels in Cycle #25 are significantly higher than those of Cycle #24, and comparable to those observed during Cycle #23. This surge in solar activity is filling the heliosphere with high-energy SEP particles, which are influencing the entire solar system, including Earth.
How to cite: Ho, G., Mason, G., Allen, R., Kouloumvakos, A., Wimmer-Schweingruber, R., Rodríguez-Pacheco, J., and Gómez-Herrero, R.: Solar Energetic Particles in Solar Cycle #25: Observations and Comparisons with Previous Cycles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2858, https://doi.org/10.5194/egusphere-egu25-2858, 2025.
Detailed analysis of solar energetic particle (SEP) events sometimes strongly suggests that the energetic particles measured by well-connected spacecraft are mainly accelerated by a coronal mass ejection (CME)-driven shock, as for example, the SEP event on 2013 August 19 or on 2022 January 20.
In this study, we analyse the relations between the solar activity and the SEP peak intensities measured by MESSENGER, STEREO and ACE spacecraft during 2010-2015. We investigate the 3D kinematic profile of the CME and associated shock wave from 1 to 15 hours and determine their main morphological (size) and dynamic (propagation and expansion speeds, acceleration) properties. We study their relationship with the main characteristics of the SEP events (for protons and electrons), such as peak flux and timing measured in situ. A summary of the results, implications for the Space Weather research, and comparison with previous works is presented.
How to cite: Rodríguez-García, L.: Acceleration of SEPs in the inner heliosphere. What CME properties account for SEP events?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8043, https://doi.org/10.5194/egusphere-egu25-8043, 2025.
Inverse velocity dispersion (IVD) in solar energetic particle (SEP) events, where higher-energy particles arrive later than lower-energy particles, is increasingly observed by spacecraft such as Parker Solar Probe (PSP) and Solar Orbiter (SolO). However, the underlying mechanisms driving IVD events are not well understood. This study examines the physical processes responsible for long-duration IVD events by analyzing the SEP event detected by SolO on June 7, 2022. The event displayed a clear and prolonged IVD signature across proton energies ranging from 1 to 20 MeV, with heavy ions exhibiting varying nose energies. Simulations indicate that evolving shock connectivity plays a crucial role in shaping the IVD signature, as SolO’s connection shifts from the shock flank to the nose over time, resulting in a gradual increase in the maximum particle energy along the field line. Furthermore, model results show that limited cross-field diffusion affects both the nose energy and the duration of the IVD event. This study highlights that long-lasting IVD events are primarily driven by evolving shock connectivity to the observer, with connections to more efficient acceleration sites at larger solar distances.
How to cite: Ding, Z. and Wimmer-Schweingruber, R.: Inverse Velocity Dispersion in Solar Energetic Particle Events Observed by Solar Orbiter, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2506, https://doi.org/10.5194/egusphere-egu25-2506, 2025.
Investigations of Solar Energetic Particle (SEP) events have long utilized the dispersive nature of onset times, i.e., earlier arrival of higher energy particles compared to lower energy populations, to infer information such as path length to an acceleration site. However, recent observations by Solar Orbiter and Parker Solar Probe have begun to characterize SEP events with an apparent “inverse velocity dispersion” (IVD) at higher energies, above a critical energy separating the classic velocity dispersion signature. These “nose”-feature SEP events may provide new insight into the impacts of magnetic connectivity to locations along an expanding CME-driven shock wave, variations of acceleration along the shock surface, and transport effects in the inner heliosphere. This presentation focuses on a statistical analysis of the occurrence rate and characteristics of IVD events observed by Solar Orbiter relative to their footpoint locations with respect to the initial flare site. While SEP events without IVDs have a broad distribution in location relative to the flare site, IVD events show a clear bias in occurrence to events with footpoints westward of the associated flare location. Implications of this spatial biasing, and impacts on the characteristics, i.e., critical energy and dispersive slope of the IVD portion of the event, is discussed in relation to recent modeling work (Ding et al., 2025). Additionally, the IVD events observed by Solar Orbiter, captured over a wide range of radial distances, is compared to a published IVD event from Parker Solar Probe near the corona at 15 solar radii (e.g., Cohen et al., 2024). These results imply that magnetic connectivity plays an important role in IVD events, particularly for those observed at larger radial distances.
How to cite: Allen, R., Ho, G., Mason, G., Cohen, C., Xu, Z., Ding, Z., Kouloumvakos, A., Wimmer-Schweingruber, R., Rodriguez-Pacheco, J., Vines, S., Filwett, R., and Dayeh, M.: The relationship of inverse velocity dispersion SEP event characteristics with footpoint location: A survey of Solar Orbiter observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4503, https://doi.org/10.5194/egusphere-egu25-4503, 2025.
Solar energetic particle (SEP) events with compositional anomalies such as the highly elevated 3He/4He ratio have been known for more than half a century, but their origin is still not well-understood. This is largely because of the difficulty of identifying their solar sources. In solar cycle 23, thanks to the availability of high-resolution coronal images from SOHO and other missions, coronal jets were found to be the typical solar manifestation of 3He-rich SEP events observed by ACE and Wind. They were often temporally correlated with type III radio bursts and electron events, which often gave the onset times with less uncertainties than the velocity dispersions of the 3He-rich SEP events themselves. The widely used technique has been to search for jets and related phenomena around the times of the type III bursts that occur in the interval that is estimated from ion data. However, data from Solar Orbiter in the present solar cycle have revealed 3He-rich SEP events whose solar sources are unidentifiable with this technique because unique jets are not found at the times of the type III bursts. In some cases, it is even hard to find a type III burst. In this work, we further investigate some of these difficult cases including the late October 2022 period, trying to find some clues in high-resolution and differently scaled EUV intensity and difference images. Other possibilities will also be pursued, including subtle changes in global magnetic field configurations (that may be related to observed dropouts) and acceleration above the low corona, etc. We also discuss how these events may change our views of the solar sources of 3He-rich SEP events that are based on previous results.
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.: On the identification of the solar sources of 3He-rich solar energetic events, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13835, https://doi.org/10.5194/egusphere-egu25-13835, 2025.
Solar energetic electron (SEE) events are one of the most common solar particle acceleration phenomena in the interplanetary space. Here we present a comprehensive study of SEE events with a fast-rise, fast-decay temporal profile on 2022 March 6, observed both by SolO/EPD at 0.5 AU and by Wind/3DP at 1 AU with a longitudinal separation of ~1° between the two spacecraft. SolO/EPD detect three SEE events at ~4-100 keV during 08:00 UT- 09:15 UT, while Wind/3DP only measures one SEE event at 0.6-66 keV between 08:00 UT and 13:00 UT. According to the velocity dispersion analysis, the solar injection’s start-time (peak-time) of the EPD first (third) event agrees with the solar injection’s start-time (peak-time) of the Wind/3DP event within uncertainties. Three SEE events observed by EPD exhibit, respectively, a single-power-law (SPL) energy spectrum with a power-law spectral index of β=3.4±0.1, a double-power-law (DPL) spectrum with a spectral index of β1=4.0±0.3 (β2=5.7±1.5) at energies below (above) a break energy of Eb=23±10 keV, and a DPL spectrum with β1=2.9±0.9 (β2=5.5±2.4) at energies below (above) a break energy of Eb=9±3 keV. The 3DP SEE event shows an SPL energy spectrum with β=3.4±0.2. At ~7 keV, the electron pitch angle width at half maximum is about 13-20° during the event peak-time for the three EPD events, while at 4 keV it is about 47° for the 3DP event. On the other hand, the first and third EPD events are likely accompanied by two HXR microflares measured by SolO/STIX, while the third event are probably associated with three EUV jects measured by SDO/AIA; the 3DP event is associated with the two HXR microflares and three jects. All these microflares/jets, as well as the magnetic field lines connecting to SolO and Wind, originate from the same active region (AR12957). Therefore, we can construct a formation scenario of these SEEs: the three events detected by SolO likely arise from different sources/processes at the Sun; as the electrons propagate from 0.5 AU to 1 AU, the three events merged into one event detected by Wind.
How to cite: Wang, L., Li, W., Ma, Q., Wimmer-Schweingruber, R. F., Krucker, S., and Mason, G. M.: Solar Energetic Electron Events Observed by Solar Orbiter and Wind on 2022 March 6, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7591, https://doi.org/10.5194/egusphere-egu25-7591, 2025.
At the CLEAR space weather center of excellence, we are building a comprehensive prediction framework for solar energetic particles (SEP) events by integrating physics-based simulations, machine learning techniques, and empirical methods. A cornerstone of this framework is the Solar Wind with Field Line and Energetic Particles (SOFIE) Model, a physics-based approach designed to predict the properties of SEP events, with a focus on the time-intensity profiles across energies ranging from 1 MeV to several hundred MeV, as well as the corresponding time-evolving energy spectra.
The SOFIE model incorporates all major factors influencing the generation and propagation of SEPs. These include: 4π maps of photospheric magnetic fields, corona (1 − 20Rs), inner and middle heliosphere (0.1 AU to Jupiter’s orbit) plasma environment, magnetic connectivity with respect to the solar source, CME initiation, SEP seed population, shock acceleration mechanisms, and energetic particle transport processes.
The background solar wind plasma in the solar corona and heliosphere is modeled by the Alfven Wave Solar-atmosphere Model(-Realtime) (AWSoM(-R)) driven by the magnetic field measurement of the Sun’s photosphere. The model's background solar wind solution is continuously updated using near-real-time, hourly GONG magnetograms. In the background solar wind, the CMEs are launched employing the Eruptive Event Generator using Gibson-Low configuration (EEGGL), by inserting a flux rope estimated from the free magnetic energy in the active region. The acceleration and transport processes are then modeled self-consistently by the multiple magnetic field line tracker (M-FLAMPA). In this work, we present the prototype of the SOFIE model, showcasing its capability to predict the time-intensity profiles and time-evolving energy spectra of SEP events, demonstrated through simulations of historical SEP events.
How to cite: Zhao, L. and Gombosi, T. and the CLEAR Team: Forecasting Time-Intensity profiles of Solar Energetic Particles using the Solar Wind with Field Lines and Energetic Particles (SOFIE) Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14356, https://doi.org/10.5194/egusphere-egu25-14356, 2025.
Solar energetic particles (SEPs) accelerated in coronal mass ejection (CME)-driven shocks are a critical factor in space weather hazards, yet significant gaps remain in understanding their acceleration mechanisms. While diffusive shock acceleration (DSA) is widely accepted as the primary process, the role of adiabatic focusing in spatially inhomogeneous magnetic fields is poorly understood within one-dimensional DSA theories. Using a Monte Carlo approach within a one-dimensional oblique shock framework, we investigated the effects of adiabatic focusing and particle escape of SEPs. Our model incorporates realistic magnetic field geometries and plasma parameters derived from the COolfluid COroNa UnsTructured (COCONUT) model. The results reveal that magnetic field inhomogeneities significantly influence particle acceleration efficiency and escape dynamics, highlighting the critical role of focusing effects. These findings provide new insights into SEP transport and acceleration, advancing our ability to accurately model particle behavior in CME-driven shocks.
How to cite: Annie John, L., Vainio, R., Afanasiev, A., and Poedts, S.: Modeling SEP Acceleration and Transport: A 1D Framework with COCONUT-Derived parameters, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19421, https://doi.org/10.5194/egusphere-egu25-19421, 2025.
It was the best of times, it was the worst of times – for two traveling interplanetary shocks observed by Solar Orbiter on November 29 and 30 in 2023. We investigate these two very dissimilar shocks which were observed within less than 27 hours to elucidate obviously present non-equilibrium features and test the assumption of gyrotropy. We find very different behavior of particles at the two shocks which are – of course – due to differences in the two shocks.
The first of the two shocks was observed at 07:51:17 on Nov. 29, 2023, was quasi-parallel (θBn ≈ 33°) and the weaker of the two shocks (fast magnetosonic (Alfvénic) Mach number of 2.4 (2.6)). It had no or only a minimal effect on the suprathermal (E less than ~1 MeV) particle population which was anisotropic and streaming away from the Sun. It was likely running into a small ICME and exhibited upstream wave activity with a dominant period just below one second.
The following shock on Nov 30, 2023 (10:47:26) was stronger (fast magnetosonic (Alfvénic) Mach number of 3.8 (4.5)) and quasi-perpendicular (θBn ≈ 81°). Wave activity upstream of this shock was weaker than at the first and limited to the shock ramp, as expected for a quasi-perpendicular shock. Upstream protons and He2+ particles show clear core-beam velocity distribution functions. Suprathermal ions upstream of the second shock are more isotropic than around the first shock but nevertheless show a clear bump-on-tail distribution which lasts for approximately two gyroperiods. The level of fluctuations of the interplanetary magnetic field (IMF) is low which probably allows this “beam” to survive. The region downstream of this shock is rich in further unusual properties of the suprathermal ions. These exhibit strong non-equilibrium features in their differential intensities and anisotropic features which suggest non-gyrotropic behavior.
How to cite: Wimmer-Schweingruber, R. F., Yang, L., Kollhoff, A., Berger, L., Kühl, P., Böttcher, S. I., Trotta, D., Kieokaew, R., Louarn, P., Fedorov, A., Rodriguez-Pacheco, J., Gómez Herrero, R., Espinosa Lara, F., Ho, G. C., Allen, R. C., Mason, G. M., and Lario, D.: A Tale of Two Shocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4447, https://doi.org/10.5194/egusphere-egu25-4447, 2025.
Electrons are a subsonic plasma species in the solar wind. Their kinetic behaviour is - to a much greater extent than the proton behaviour - the result of an interplay between global properties of the heliosphere and local plasma processes. The global properties of the heliosphere include the interplanetary electrostatic potential, the large-scale interplanetary magnetic field, and the density profile of the plasma. The local plasma processes include collisions, wave-particle interactions, and turbulence. Through this interplay, the electron distribution function develops interesting kinetic features that are observable in situ. In addition to a quasi-Maxwellian core, the distribution exhibits suprathermal populations in the form of the strahl and halo components as well as cut-offs due to loss effects in the interplanetary potential.
We discuss the interaction of suprathermal electrons with local structures such as compressive waves and magnetic holes, and the impacts of these structures on the global electron transport in the heliosphere. The regulation of the electron heat flux is of particular interest in this context. We support these results with observations from Solar Orbiter and Parker Solar Probe.
How to cite: Verscharen, D., Coburn, J., and Liu, J.: Modulation of suprathermal electrons and their heat flux in compressive plasma structures in the solar wind, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5198, https://doi.org/10.5194/egusphere-egu25-5198, 2025.
Velocity dispersion (VD) is a common feature of solar energetic particle (SEP) events, in which particles with higher kinetic energies (and thus higher speeds) arrive earlier than those with lower energies. However, recent observations by the Solar Orbiter (SolO) mission have identified a series of SEP events with a previously not reported feature in which particles with higher energies arrive later, apparently exhibiting inverse velocity dispersion (IVD). We analyse several such SEP events and suggest two explanations for this effect: 1) changes in magnetic connectivity between the observer and the outward-propagating shock which continuously accelerates particles; 2) the acceleration time for higher-energy particles is longer during the diffusive shock acceleration process so that they are released later. These observations provided a first opportunity to quantify the energy-dependent release process which greatly advances our understanding of the particle acceleration process.
How to cite: Li, Y., Guo, J., Pacheco, D., Wang, Y., Temmer, M., Ding, Z., and Wimmer-Schweingruber, R. F.: The first observation of later arrival of more energetic particles during solar eruptions observed by the Solar Orbiter mission, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14047, https://doi.org/10.5194/egusphere-egu25-14047, 2025.
A sustained gamma-ray emission (SGRE) event from the Sun was observed on 2024 September 9 by the Large Area Telescope (LAT) on Fermi satellite at energies >100 MeV. SGRE requires the precipitation of >300 MeV protons deep into the photosphere. The SGRE event was associated with a shock-driving coronal mass ejection (CME) that originated ~40 degrees behind the east limb of the Sun. The event was observed by multiple spacecraft such as the Solar and Heliospheric Observatory (SOHO), Solar Terrestrial Relations Observatory (STEREO), Parker Solar Probe (PSP), Solar Orbiter (SO), Solar Dynamics Observatory (SDO), Wind, and GOES, and by ground-based radio telescopes. Based on observations from SO’s Spectrometer Telescope for Imaging X-rays (STIX), we estimate that the eruption location to be S17E129. GOES observed a large solar energetic particle (SEP) event but only in the >10 MeV energy channel because of poor magnetic connectivity. However, SO was well-connected to the eruption region and hence observed high-energy particles. We infer that >300 MeV particles from the extended shock precipitated on the frontside of the Sun to produce the SGRE event. Forward modeling of the CME using SOHO and STEREO observations indicate that the CME flux rope had high initial acceleration of the CME (`2.5 km s-2), high speed (2500 km s-1), and associated with type II bursts in the metric to decameter-hectometric (DH) wavelengths. All these properties are characteristic of frontside CMEs that are associated with SGRE events. Furthermore, the durations of SGRE and type II burst are similar as in longer duration (>3 hours) SGRE events.
How to cite: Gopalswamy, N., Makela, P., Xie, H., Akiyama, S., Yashiro, S., Bale, S., Wimmer-Schweingruber, R., and Krucker, S.: Transport of high energy protons from a backside solar eruption to produce gamma-ray emission on the front side of the Sun, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16916, https://doi.org/10.5194/egusphere-egu25-16916, 2025.
Title: Investigating Solar Sources of 3He-Rich and 3He-Poor SEP Events in 2024 using
Solar Orbiter HET
Authors:
Sindhuja. G1, Robert F. Schweingruber1, Patrick Kühl1, Alexander Kollhoff1, Zheyi Ding1, Sebastian
Fleth1, Lars
Berger1, Javier Rodriguez-Pacheco2, George C. Ho3, Glenn M. Mason4, Raul Gomez-
Herrero2, Francisco Espinosa Lara2, Ignacio Cernuda2, Stephan Böttcher1, Sandra Eldrum1, and
Robert C. Allen3,
1) Institute of Experimental and Applied Physics, Kiel University, Leibnizstaße 11, DE-24118
Kiel.
2) Universidad de Alcalá, Space Research Group, 28805 Alcalá de Henares, Spain
3) Southwest Research Institute, San Antonio, TX, USA
4) Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
Abstract:
This study focuses on the solar sources of 3He-rich and 3He-poor solar energetic particle
(SEP) events observed in 2024, utilizing data from the High-Energy Telescope (HET) onboard
the Solar Orbiter mission. The HET instrument, which measures the energy spectra of energetic
particles—including helium and protons—operates in the energy range of ~7–500 MeV/nucleon
and provides critical insights into particle acceleration in the inner heliosphere. The SEP
events were selected based on specific criteria: comparable 3He/4He ratios in Suprathermal Ion
Spectrograph (SIS) and HET at 8.2 MeV data, a Type III radio burst association with the event,
and an increase in electron flux within the 10-100 MeV energy range. These events include both
3He-rich and 3He-poor types, providing an opportunity to explore the differences in their
solar origins.
In particular, 3He-rich events are significant as they offer valuable insights into the mechanisms
of particle acceleration and transport associated with coronal mass ejections (CMEs). Our
analysis aims to compare the energy spectra and particle composition between 3He-rich and
3He-poor events, shedding light on the underlying physical processes that govern these
phenomena. By examining the solar sources of these distinct event types, we seek to uncover the
factors contributing to variations in helium content and acceleration mechanisms.
Furthermore, we present the kinematics of associated CMEs and flare properties, offering a comprehensive
view of the dynamics behind these SEP events. This study is expected to enhance our
understanding of the role of helium-rich events in the solar wind and their potential impacts on
Earth's magnetosphere, ultimately contributing to the broader comprehension of heliospheric dynamics
and solar particle acceleration processes.
How to cite: gunaseelan, S., F. Schweingruber, R., Kühl, P., Kollhoff, A., Ding, Z., Fleth, S., Berger, L., Pacheco, J. R., Ho, G. C., Mason, G. M., Herrero, R. G., Espinosa Lara, F., Cernuda, I., Böttcher, S., Eldrum, S., and Allen, R. C.: Investigating Solar Sources of Helium-Rich and Helium-Poor SEP Events in 2024 using Solar Orbiter, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6608, https://doi.org/10.5194/egusphere-egu25-6608, 2025.
The Sun constantly emits a stream of charged particles, e.g. electrons and protons which is called the solar wind. In addition to this low energetic background, Solar Energetic Particle (SEP) events occur and are observed by Solar Orbiter in the inner heliosphere. Here, we are interested in the electron component of SEP events. The Electron Analyzer System (EAS) and the SupraThermal Electron Proton (STEP) sensor on Solar Orbiter measure electrons in the energy range from 1 eV to 5 keV and 2 keV to 60 keV, respectively. The field of view of STEP overlaps with the field of view of the EAS 1 sensor head. SEP events are identified in the STEP data and compared with the electron signal in the EAS data. We utilize this overlap to evaluate the electron measurements in STEP and EAS for at least one selected SEP event. During electron SEP events and times where most of the higher energy bins in EAS 1 are populated, the one dimensional differential energy flux spectra show an overlap within the respective uncertainties. SEP events typically show a velocity dispersion. In a Velocity Dispersion Analysis (VDA), for each energy channel an onset time for the event is determined. Due to the reduced quantum efficiency in the highest energy channels of EAS, higher fluxes are required to detect an SEP event in EAS than in STEP. To increase the signal to noise ratio for the SEP events, EAS bins in all three measurement dimensions, i.e. azimuth, elevation and energy, are chosen depending on the pitch angle coverage of the event. Anisotropic SEP events cover fewer instrumental bins in EAS than isotropic events. To test the uncertainty of the onset times depending on the method several approaches are compared, including a manual identification and the Poisson CUSUM method on the EAS Level 1 count data. The selected event illustrates the importance of considering an energy dependent minimal detection threshold in VDA since VDA relies on the assumption that the earliest detected particles for each energy are indeed the first particles that reach the spacecraft. The VDA is then applied to the STEP data and the results are compared with the EAS results. The instrumental and quantum efficiency driven onset times influence the approximation of the release time of the accelerated particles at the acceleration time, i.e. in the solar corona while neglecting transport effects along the way to the spacecraft. All in all combining EAS and STEP gives us several advantages. (1) It allows us to evaluate the calibration of both instruments. (2) With EAS the VDA is extended to lower energies. (3) In addition the full 360° field of view of EAS helps us to evaluate the anisotropy of SEP events outside the field of view of STEP which are strong enough to produce a signal in the higher EAS energy bins.
How to cite: Jentsch, E., Heidrich-Meisner, V., and Wimmer-Schweingruber, R. F.: Investigating electrons in SEP events observed by Solar Orbiter/EPD/STEP and Solar Orbiter/SWA/EAS with Velocity Dispersion Analysis , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18931, https://doi.org/10.5194/egusphere-egu25-18931, 2025.
The sources and origins of solar energetic particles (SEPs), especially for the GeV-level events, are the premise and fundamental issue for SEP-induced space-weather disasters. Observational evidence indicates that the anisotropy properties exist in the 3D large temporal-spatial turbulence magnetic reconnection(3D LTSTMR) in solar activities, which is essential to understanding the energy conversion between magnetic energy and acceleration energy (bulk kinetic energy) and heating energy (thermal kinetic energy) over different particle species (e.g., electron, ion, 3He/4He, and other heavier particles), and SEPs characteristics and acceleration propagation in non-ideal diffusion regions. In this work, on the supercomputer platform (GPU heterogeneous architecture & ARM architecture), a 3D spherical coordinates system (
) for flare loop 3D LTSTMR is applied to explore the helical turbulence-induced anisotropic characteristics (TAC, including turbulence anisotropy, TA; turbulence intensity, TI; and spectral anisotropy properties) through the improved relativistic hybrid particle-in-cell and lattice Boltzmann (RHPIC-LBM2) code. Firstly, we deduced the explicit expression of the turbulence-induced dissipation-diffusion (TIDD) terms under fully coupled hydro-dynamic-kinetic continuous scales by considering the turbulence-resistance-induced self-generated organization and the turbulence-viscosity-induced self-feeding-sustaining with filter theory. Then, we improved the input module and dissipation-diffusion module and added a new TIDD module in the original RHPIC-LBM model algorithm code. Finally, we analyze the TAC in the impulsive twisted multi-magnetic flux ropes (MFLs) & multi-current plasma flux ropes (CFLs) & multi-plasma flux ropes (PFLs). It is found that the magnetic strength (MFLs), current density (CFLs), and charged flow (PFLs, electron, ion, 3He/4He) anisotropy exist and vary in different evolution times (65.6000s to 74.3467s) in the different direction (
plane, 
plane), in the different scale (R=24Mm) at B&U decoupled frozen-in condition broken region. The main findings of the present study are as follows: 1) The TAC in the radial direction is stronger than in the azimuthal direction ( plane) and in the polar direction ( plane); 2) The TAC of magnetic strength (MFLs), current density (CFLs), and charged flow (PFLs) do not overlap in the evolution process; 3) The TAC increases with the evolution time and reaches its maximum when the turbulence enters the fully developed stage; 4) The TAC decreases with the decreasing scale and exhibits weakness when entering the micro-kinetic scale. We anticipate these results to be a key point and give new insights for evaluation of the short-time real-time extremely GeV-SEPs prediction (GPU heterogeneous architecture) and the real-time long-time SEP monitor (ARM architecture), which serve for the 'China Science Development Strategy: Space Science (2020-2035)', and 'The Strategic Position of Space Astronomy: China's Space Science 2035 Development Strategy' in NSFC&CAS. and 'National Mid- and Long-term Plan for Space Science in China (2024-2050).
URL: Share files：EGU2025_anis...ics[Folder] Cloud disk link：https://pan.cstcloud.cn/s/Xt4ZjsrR3s
How to cite: Zhu, B.: Investigation of the anisotropic characteristics in the flare loop turbulence magnetic reconnection through improved RHPIC-LBM on the supercomputer platform , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3936, https://doi.org/10.5194/egusphere-egu25-3936, 2025.
Multiple interplanetary coronal mass ejections (ICMEs) and the shocks they drive sometimes form shock-ICME interaction regions, where suprathermal electrons can undergo complex and not yet fully understood physical processes. To enhance our understanding of electron acceleration and transportation in these regions, we will present a comprehensive study of a shock-ICME interaction case based on multi-spacecraft observations. From November 29th to December 2nd, 2023, four ICMEs and three ICME-driven shocks were successively observed by SolO (0.84 AU), STEREO-A (0.97 AU), and Wind (0.99 AU), with a maximum longitudinal separation of ~17°. First, we will analyze the electron pitch angle distributions to constrain scattering and/or reflection effects at each location. Secondly, we will self-consistently characterize the energy spectral features of these suprathermal electrons using a recently proposed extended pan-spectrum fitting method (Li et al., 2025). These features will help reveal the origin, acceleration, and transportation processes of suprathermal electrons observed in shock-ICME interaction regions, particularly the different physical scenarios occurring at each interaction phase. Finally, we will compare these suprathermal electrons with those observed near typical interplanetary shocks, in order to assess whether shock-ICME interaction regions provide more efficient acceleration for suprathermal electrons.
How to cite: Ma, Q. and Wang, L.: Multi-spacecraft Observations of Interplanetary Suprathermal Electrons in a Shock-ICME Interaction Region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8856, https://doi.org/10.5194/egusphere-egu25-8856, 2025.
We report the energetic proton dynamics around an interplanetary shock driven by a coronal mass ejection (CME). We use the high-resolution EPT instrument onboard the Solar Orbiter to study the local acceleration process of energetic protons. The interplanary shock is observed by the Solar Orbiter on March 14th 2023 at 0.6 au. A magnetic structure is also present 7-minute upstream the shock. The magnetic structure manifests as a BN reservsal and mangetic depression with asymmteric magnetic magnitude on each side. A detailed analysis suggests that the magnetic structure is possibly related to a magnetic reconnection. The magnetic reconnection region is partially crossed by the Solar Orbiter, which passes through the reconnection upstream, the diffusion region and an extended exhaust region in sequence. Upstream the structure, the proton differential flux anisotropy is constant which is dominated by the parallel-propagating energetic protons from the shock. Interestingly, a bipolar-like flux anisotropy is present between the magnetic structure and the shock, while B_R>0 is satisfied all the time. This suggests that some local physical processes may play a role in proton acceleration due to the presence of magnetic reconnection. We also compare the flux spectra upstream and downstream the structure, the spectral indices of which are very different. Our work highlights the importance of magnetic structures/reconnection in particle acceleration, even when the structure is close to the shock.
How to cite: Zhu, X. and Yang, L.: Proton acceleration during the interaction of magnetic structure with interplanery shock, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14525, https://doi.org/10.5194/egusphere-egu25-14525, 2025.
Context. The Energetic Particle Detector (EPD) suite onboard Solar Orbiter provides unprecedented high-resolution measurements
of suprathermal and energetic particles in interplanetary space. These data can resolve particle dynamics near interplanetary shocks,
offering new insights into particle acceleration and transport processes.
Aims. We present observations of energetic proton bursts downstream of an interplanetary shock and discuss possible acceleration
and formation processes.
Methods. We combined data from two sensors of EPD, the SupraThermal Electron Proton (STEP) sensor and the Electron-Proton
Telescope (EPT), to investigate the proton bursts across the full energy range. We examined the dynamic energy spectra, temporal
flux profiles, pitch-angle distributions, and spectral features of these proton bursts.
Results. We find that these proton bursts travel anti-parallel to the interplanetary magnetic field (IMF) in a region where the IMF
is pointing southward, substantially out of the ecliptic plane. These bursts typically last for ∼10-20 s and span a wide energy range
from ∼20 to ∼1000 keV. Their energy spectra typically show an evident bump in the ∼20-100 keV range, characterized by a valley at
∼20-30 keV, a peak at ∼40-50 keV, a full width at half maximum of ∼30 keV, and a positive spectral slope of ∼1 between the valley
and peak. These proton bursts exhibit no velocity dispersion feature and their occurrences do not coincide with significant changes in
the IMF direction or with enhancements in the 4-100 kHz electric potential oscillations or the 0.1-4 Hz magnetic field fluctuations.
Conclusions. These results suggest that the proton bursts could originate from a source below the ecliptic plane, probably the part
of the shock situated there. These protons could be accelerated through shock-drift acceleration or shock-surfing acceleration, with
varying efficiencies at different parts of the source. The observed spectral bumps likely result from transport effects affecting the
low-energy ∼10-50 keV protons.
How to cite: Yang, L., Li, X., Heidrich-Meisner, V., Wimmer-Schweingruber, R., Wang, L., Kollhoff, A., Zhu, X., Nicolaou, G., Ding, Z., Berger, L., Liu, H., Rodríguez-Pacheco, J., Mason, G., and Ho, G.: Energetic proton bursts downstream of an interplanetary shock, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5824, https://doi.org/10.5194/egusphere-egu25-5824, 2025.
This study examines the impact of non-local phenomena on the transport of energetic particles, which are frequently observed in interplanetary space near collisionless shocks. The prevailing theory of particle acceleration at shocks, known as diffusive shock acceleration (DSA), is based on the standard diffusion equation and predicts a specific density profile for energetic particles: upstream of the shock, the density is expected to exhibit exponential growth, while downstream, it should form a constant, flat profile. However, these predictions often conflict with observations around shocks in interplanetary space. In practice, data analysis and numerical simulations indicate a long power-law-like upstream density profile, while the downstream region exhibits a decreasing, non-flat density profile. This discrepancy leads to consider of a modified version of the ordinary Fick's law relating the macroscopic diffusive flux of energetic particles with the number density. As described by Calvo et. al (2007), in this formulation the spatial derivative of the number density is replaced by an extended spatial integration of a function depending on the density profile multiplied by a statistical weight that decreases with increasing distance from the point where the flux is being evaluated, which yields a non-local diffusive flux. Such expression is called the Fractional Fick's Law as it involves fractional order derivatives. It can be shown that substituting this fractional flux into the continuity equation recovers the Fractional Diffusion Equation describing superdiffusion, that is, an anomalous diffusion regime in which the mean square displacement of particles grows super-linearly with time. We use a numerical Fortran 90 code for evaluating the fractional flux using the trapezoidal rule for integration. After verifying that the numerical method used is consistent and correct, this code is tested using the density profiles of accelerated particles at a numerically simulated shock in two scenarios: one involving normal diffusion and the other involving superdiffusion. Notably, in both cases, a downstream negative flux is observed, indicating the presence of uphill transport, i.e., transport in the same direction as the density gradient. Finally, the fractional flux is numerically evaluated using data from the ACE and Wind spacecrafts for two different shock crossings. In both events, uphill transport is observed, which is an intriguing and counterintuitive result that allows for the correct interpretation of satellite observations, as well as shedding light on the physical processes underlying the acceleration of energetic particles at space and astrophysical shocks.
How to cite: Simone, M., Zimbardo, G., Perri, S., and Prete, G.: Fractional Fick's Law and Anomalous Transport of Energetic Particles at Interplanetary Shocks., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6809, https://doi.org/10.5194/egusphere-egu25-6809, 2025.
The presence of energetic electrons in the heliosphere is associated with solar eruptions, but details of the acceleration and transport mechanisms are still unknown. We explore how electrons interact with shock waves under the assumptions of shock drift acceleration (SDA), diffusive shock acceleration (DSA), and stochastic shock drift acceleration (SSDA). Consideration of the shock wave parameter space, such as shock speed, shock obliquity, shock thickness, and plasma density upstream of the shock, helps determine electron spectra and their highest energies. With suitable simulation parameters, the model is able to accelerate thermal electrons to relativistic energies and, additionally, to produce an electron beam upstream of the shock wave, a requirement for the type II radio burst seen in radio observations associated with shock waves and particle acceleration.
This presentation delves into the results of the presented model in regards to electron acceleration and transport within shock waves, contributing to our understanding of solar and interplanetary phenomena and their practical applications in space weather forecasting.
Additionally, the model is developed to be an easy-to-use open source tool for understanding observations of high energy electron populations and the ensuing highly localized radio bursts, integration to other heliosphere plasma models through wrappers, and teaching modeling of particle acceleration in a high-performance computing setting.
This study has received funding from the European Union's Horizon Europe research and innovation programme under grant agreement No 101134999 (SOLER). The presentation reflects only the authors' view and the European Commission is not responsible for any use that may be made of the information it contains.
How to cite: Nyberg, S., Afanasiev, A., Vainio, R., and Vuorinen, L.: Simulating electron acceleration in shocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13267, https://doi.org/10.5194/egusphere-egu25-13267, 2025.
The primary source of suprathermal particles is in the solar corona. These particles are generally considered a seed population to be accelerated to solar energetic particles by coronal mass ejection shocks. Their distribution in the corona is vital for us to understand the production of solar energetic particles. During propagation through interplanetary space, the properties of suprathermal particles can change dramatically by various transport mechanisms, such as scattering, adiabatic cooling, and stochastic acceleration. To link observations made in the interplanetary space to particle distribution in the solar corona, we have developed a focused transport to calculate the propagation effect. This paper will present focused transport model calculations to show how particle scattering and acceleration can affect the evolution of the suprathermal particle spectrum and anisotropy in interplanetary space.
How to cite: Zhang, M.: A focused transport model of suprathermal particles in the interplanetary medium, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14948, https://doi.org/10.5194/egusphere-egu25-14948, 2025.
We present a model of the magnetic field in the heliosphere. Our model's magnetic field is made of a large-scale component, modeled as the Parker Spiral, and a small-scale turbulence component, modeled through a wavelet-based method. The turbulent component is tailored to reproduce a few key properties of magnetic fluctuations in the Parker Spiral, such as a varying correlation length and a decreasing turbulence amplitude as a function of the radial distance from the Sun. The wavelet-based method is obtained from a previously developed Cartesian method by defining a new set of coordinates to ensure the correct scaling of the turbulence correlation length as a function of the radial distance. Our algorithm allows for reproducing a larger spectral range of fluctuations than magnetohydrodynamic simulations, which is needed to properly describe the gyroresonant scattering of energetic particles. In the future, the model will be used to study energetic particle propagation in the heliosphere.
How to cite: Pucci, F., Malara, F., Larosa, A., Pezzi, O., and Perri, S.: Wavelet-based modeling of the heliospheric turbulent magnetic field, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4800, https://doi.org/10.5194/egusphere-egu25-4800, 2025.
Populations of energetic particles, ranging from solar energetic particles to incredibly high-energy cosmic rays, are ubiquitous in space and astrophysical plasmas. Several intertwined phenomena, including shocks, magnetic reconnection, jets, and turbulence, are responsible for the efficient energization of particles and for determining their transport properties.
Plasma turbulence produces patchy coherent structures, such as reconnecting current sheets, plasmoids, and vortices across a vast range of spatial scales. Under some circumstances, these structures can entrap particles, thus providing fast energization through, for example, drift acceleration. I will review some of these mechanisms and outline recent numerical efforts aimed at investigating how coherent structures, such as large-scale eddies or flux ropes, impact particle transport and energization. I will also comment on the applicability of these results in space and astrophysical contexts.
How to cite: Pezzi, O., Trotta, D., Benella, S., Sorriso-Valvo, L., Malara, F., Pucci, F., Meringolo, C., Matthaeus, W. H., and Servidio, S.: The role of coherent turbulent structures in influencing particle transport and energization, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4592, https://doi.org/10.5194/egusphere-egu25-4592, 2025.
