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.

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 B_N 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.

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.