The overall goal of Solar Orbiter is to understand how the Sun creates and controls the heliosphere. The mission provides unprecedented imaging of the Sun’s photosphere, chromosphere, and corona, enabling studies of the origin and evolution of the Sun’s atmosphere, the solar wind, solar eruptions, and energetic particle events. The combination of high-resolution imaging and simultaneous in-situ measurements from Solar Orbiter’s inner-heliospheric vantage point offers a unique opportunity to link solar sources directly to their heliospheric impacts.
This session invites contributions that address the Solar Orbiter science objectives, exploit multi-mission data sets, and studies of the connections between the Sun and the heliosphere. We also welcome Solar Orbiter-related contributions in the fields of theory and numerical simulations that contribute to a better understanding of the solar origins of heliospheric variability and space weather.
Orals: Mon, 4 May, 08:30–10:05 | Room L1
This presentation will provide a status update of the ESA/NASA Solar Orbiter mission and summarise recent science highlights.
Solar Orbiter has been acquiring unique data from as close as 0.29 au solar distance since 2022, combining in situ measurements close to the Sun with simultaneous high-resolution solar imaging and spectroscopic observations. These multi-instrument data have enabled the science community to address fundamental solar physics questions, including determining the linkage between observed solar wind streams and their source regions on the Sun. Solar Orbiter’s science return is significantly enhanced by coordinated observations with other space missions, as well as ground-based telescopes.
In 2025, Solar Orbiter’s out-of-ecliptic mission phase started, acquiring first detailed observations of the Sun’s unexplored polar regions from 17° heliolatitude. During its proposed mission extension, Solar Orbiter will successively increase its maximal inclination to 24° in January 2027, 30° in April 2028 and 33° from July 2029 onwards. This phase is opening a new frontier in solar physics, with the prospect of revolutionising our understanding of magnetic flux transport and the solar dynamo.
How to cite: Müller, D., Janvier, M., De Groof, A., Williams, D., Walsh, A., Fischer, C., Osuna, P., Nieves, T., and Lario, D.: Solar Orbiter: Mission status and science highlights, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18646, https://doi.org/10.5194/egusphere-egu26-18646, 2026.
The extreme-ultraviolet (EUV) brightenings identified by Solar Orbiter, commonly known as “campfires”, are one of the fine-scale transient brightenings detected in the solar corona. Using closest-perihelion observations of Extreme-Ultraviolet Imager (EUI) onboard Solar Orbiter, recently we have reported the presence of smallest and shortest-lived EUV brightenings in the quiet-sun to date. We will present the spatio-temporal distribution of EUV brightenings over different magnetic environments of the solar atmosphere and discuss their role in coronal heating. By using various sets of quiet-sun and coronal-hole observations from HRIEUV/EUI we will present a comparative analysis of morphological and photometrical properties of EUV brightenings. We will discuss the interlinks of EUV brightenings to the photospheric dynamics and magnetic field distribution using HRT/PHI observations. Further their potential coupling through the solar atmosphere will be addressed using SPICE and IRIS observations.
How to cite: Narang, N., Verbeeck, C., Berghmans, D., Mierla, M., Parenti, S., Auchere, F., Chitta, P., and Calchetti, D.: Influence of magnetic-field distribution on the spatio-temporal properties of EUV brightenings in the solar atmosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19475, https://doi.org/10.5194/egusphere-egu26-19475, 2026.
Magnetic switchbacks, often observed in the near-Sun solar wind, have received increased interest in recent years due to their potential role in mediating the heating and acceleration of the solar wind, but their origin remains debated. In this work, we present a coordinated observation of a switchbacks cluster by BepiColombo (0.35 au) and Solar Orbiter (0.67 au), obtained during the alignment between 6-8th October 2021, which enabled the direct investigation of switchbacks evolution across heliocentric distances. In particular, the stream observed by the spacecraft can be tracked back to the boundary of an equatorial coronal hole. Plasma and magnetic field data measured in-situ exhibit remarkable similarities at both locations. In particular, larger-scale switchbacks exhibit strong sub-linear expansion, thus appearing almost unevolved in morphology during the propagation when the spacecraft cutting-angle effect is taken into account. The stable magnetic configuration of the analyzed switchbacks suggests that they can be identified as small-scale flux ropes. Indeed, for shear-driven instabilities triggered by stream interaction with the background slow wind, short-living (one eddy turnover time, $\tau \sim 1$ hr) switchbacks would be expected compared to the travel time from BepiColombo to Solar Orbiter ($\sim 38$ hr). These findings provide critical insights on switchbacks origin and evolution, potentially constraining future phenomenologies on their formation. A useful consequence of our observations is that statistical analyses on switchbacks evolution should always account for the cutting-angle effect.
How to cite: Stumpo, M., Benella, S., Di Bartolomeo, P. P., Milillo, A., Heyner, D., Nicolaou, G., Varsani, A., Larosa, A., Pezzi, O., Trotta, D., Laurenza, M., D'Amicis, R., Laky, G., and Jeszenszky, H. and the BepiColombo/MPO-MAG TEAM: Long-lived magnetic switchbacks tracked across 0.32 au through BepiColombo-Solar Orbiter radial alignment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21309, https://doi.org/10.5194/egusphere-egu26-21309, 2026.
In this work we incorporate Solar Orbiter’s Polarimetric and Helioseismic Imager (PHI) Full Disc Telescope (FDT) observations into the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model to construct more complete global solar photospheric maps. We feed these maps into the Wang-Sheeley-Arge (WSA) model to reconstruct the solar corona and perform solar wind simulations for a period of two months in 2024 at multi-spacecraft locations (Solar Orbiter, PSP, ACE, STEREO-A). We assess the quality of our predictions, and compare our results when no FDT data have been employed in order to understand how the addition of far side information affects the open magnetic field topologies on the Sun, their connectivity with various spacecraft of interest, the shape and structure of the heliospheric current sheet, as well as the solar wind predictions at different points in the interplanetary space. Our results demonstrate the value of incorporating far-side information in improving the heliospheric modeling and forecasting globally, as well as the significance of 4pi continuous monitoring of the Sun for more reliable space weather predictions overall.
How to cite: Samara, E., Arge, C. N., Schonfeld, S., Farrish, A., Henney, C., Nieves-Chinchilla, T., and Wallace, S.: The influence of Solar Orbiter/PHI far-side information on coronal holes and solar wind predictions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7556, https://doi.org/10.5194/egusphere-egu26-7556, 2026.
Stream interaction regions (SIRs) are formed where high-speed streams from coronal holes expand into slower preceding solar wind. Simulations have long shown significant latitudinal structuring to SIRs and their associated energetic populations, which have been additionally suggested from high-latitude Ulysses observations. However, multi-point observations of SIRs from observers at different latitudes are needed to constrain this variability. This includes better understanding the role of coronal hole properties and impacts of latitudinal variability in the preceding slow solar wind streams on the evolution of SIR structures. In this presentation, we focus on recent off-ecliptic Solar Orbiter observations in comparison with observations at ACE and STEREO-A to further explore the importance of latitudinal structuring of SIRs and associated energetic particles.
How to cite: Allen, R., Ho, G., Mason, G., Walker, M., Davis, S., Wimmer-Schweingruber, R., Rodriguez-Pacheco, J., Vines, S., Li, G., Filwett, R., and Dayeh, M.: Latitudinal Variability of Stream Interactions Regions: Multi-spacecraft Comparisons with Solar Orbiter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12435, https://doi.org/10.5194/egusphere-egu26-12435, 2026.
Since April 2023, solar flares have been simultaneously observed by the Spectrometer/Telescope for Imaging X-ray (STIX) onboard ESA’s Solar Orbiter and by the Hard X-ray Imager (HXI) onboard the Chinese ASO-S mission. The two telescopes independently measure 2D Fourier components (visibilities) of the flaring X-ray radiation from different vantage points. However, by combining their datasets, it is possible to obtain a sampling of the 3D Fourier transform of thermal hard X-ray sources in solar flares. This combined dataset allows reconstructing the 3D morphology of the flaring sources by solving an inverse imaging problem.
In this presentation, we describe the methodology we developed for 3D reconstruction of thermal hard X-ray sources in solar flares from combined STIX/HXI data. We present the results obtained in the case of the X9.1 GOES class event which occurred on October 3, 2024. During this event, the two instruments were in an ideal configuration, where the separation angle between them and the flaring site was approximately 90 degrees. We validate the 3D reconstruction by comparing them with the 2D images independently reconstructed from STIX and HXI data. Finally, we determine the altitude of the reconstructed X-ray source above the solar surface as a function of time, and we derive estimates of its radial velocity.
How to cite: Palumbo, B., Massa, P., Stiefel, M., Ryan, D., Collier, H., Su, Y., Piana, M., and Krucker, S.: 3D reconstruction of thermal hard X-ray sources in solar flares from combined STIX and HXI visibilities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12658, https://doi.org/10.5194/egusphere-egu26-12658, 2026.
The transport of solar energetic particles (SEPs) through the heliosphere is governed by the interplanetary magnetic field (IMF) embedded in the solar wind plasma. Large-scale fluctuations in the IMF give rise to the transient variation in SEP intensities. Here, we present Solar Orbiter (SolO) observations of a distinct class of SEP flux variations: short-timescale (~1 hr) directional flux reversals (DFRs). Data from the Energetic Particle Detector (EPD) reveal that these reversals are a common feature in SEP events, occurring simultaneously across a wide energy range (keV to tens of MeV) and exhibiting steep intensity gradients. Unlike classic 'dropout' events—where intensity decreases isotropically—DFRs display a asymmetric signature where a intensity drop in one direction coincides with a spike in another. These intermittent variations are associated with flux-rope magnetic structures and distinct solar wind properties, which serves as direct evidence that the spacecraft has encountered a new solar wind stream with a different magnetic field connectivity. These observations demonstrate that SEPs act as an effective probe of solar wind structures, providing new insights into their nature.
How to cite: Chen, X. and Li, G.: Probing Solar Wind Structures with Solar Energetic Particle Observations from Solar Orbiter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17968, https://doi.org/10.5194/egusphere-egu26-17968, 2026.
We present a comprehensive catalogue of 212 Solar Energetic Particle (SEP) events observed by the High Energy Telescope (HET) of the Energetic Particle Detector (EPD) onboard Solar Orbiter during the ascending and maximum phases of Solar Cycle 25 (2020–2025). The survey is based on combined measurements of approximately 1 MeV electrons and 8 MeV protons, and includes a substantial subset of events with proton energies exceeding 25 MeV and 50 MeV, providing broad coverage of energetic particle conditions in the inner heliosphere. SEP events were identified through statistically significant enhancements above background levels. For each event we derived key parameters, including onset and peak times, peak intensities, fluences, and electron-to-proton (e/p) ratios. Particle release times at the Sun were estimated using both time-shifting and velocity-dispersion analysis (VDA) techniques. These release times were compared with observations of solar flares and associated coronal mass ejections (CMEs) in order to identify the most probable parent solar sources and to investigate the relationship between SEP characteristics and eruption properties. In situ measurements of the solar wind plasma and interplanetary magnetic field were further employed to characterize the heliospheric environment of each event and to compute magnetic connection angles, enabling an assessment of the role of magnetic connectivity in SEP onset and intensity. We also examine the diagnostic value of e/p ratios and elemental abundance signatures for distinguishing between impulsive and gradual SEP events. As part of this work, we developed two open-source tools—SEP-PACT for catalogue construction and VDA for release-time analysis—available via the SPEARHEAD GitHub repository (https://github.com/spearhead-he). The complete catalogue will be released through Zenodo and the SPEARHEAD web interface (https://spearhead-he.eu), providing a valuable resource for future studies of SEP acceleration and transport in the inner heliosphere.
Acknowledgement: The is work has received funding from the European Union’s Horizon Europe programme under grant agreement No 101135044 (SPEARHEAD).
How to cite: Papaioannou, A. and the SPEARHEAD Collaborative Network: Solar Energetic Particle Events in the Inner Heliosphere: Observations from Solar Orbiter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19554, https://doi.org/10.5194/egusphere-egu26-19554, 2026.
Solar flares and associated eruptions are a known source of solar energetic particles (SEPs), but it is often challenging to establish a precise link between individual flares and SEP events measured in-situ throughout the heliosphere. The Solar Orbiter mission, with its Spectrometer/Telescope for Imaging X-rays (STIX) and Energetic Particle Detector (EPD), provides excellent measurements for systematic studies of these phenomena. Based on these data, we developed an algorithm that automatically links solar flares to SEP electron events using a STIX flare list, SEP electron measurements from EPD, and considering model predictions of magnetic connectivity between the Sun and the spacecraft. As a result, the method identifies several hundred flares to be connected to SEP events - out of more than 25000 flares detected with STIX between 2021 and 2025. The precise linkage criteria can be set by the user - including the accepted distance between flare and modelled magnetic footpoint and the length of the accepted time window for SEP arrival. A first comparison of the automatic method with the CoSEE-Cat electron event catalogue for the time period 2021 - 2022 shows, that about 50% of the links found by the algorithm are actual physical links. The method is already available as quick-look online tool for flare-SEP linkage.
How to cite: Janitzek, N., Jentgens, H., Kistler, F., Bischof, L., Stiefel, M., Barczynski, K., Zhu, Y., Harra, L., Gomez-Herrero, R., Warmuth, A., Rouillard, A., Wimmer-Schweingruber, R., Rodriguez-Pacheco, J., and Krucker, S.: An automated approach to link solar flares and energetic particle events measured with Solar Orbiter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16991, https://doi.org/10.5194/egusphere-egu26-16991, 2026.
The Proton Alpha Sensor (PAS), part of the Solar Wind Analyzer (SWA) onboard Solar Orbiter, has been designed to measure the full 3D ion velocity distribution function (VDF) at time cadence larger than one sample per second, thus, faster than the typical proton cyclotron period (Burst mode). Unfortunately, due to software difficulties, this capability to explore ion kinetic processes has been only activated during the first months of operation (2020-mid 2021) so that the ‘normal mode’ cadence (1 VDF each 4 s) was systematically used from 2021 to 2024. After in-depth analysis, a new software version has finally been implemented at the end of 2024, restoring in part the PAS burst mode capability. As a result, an impressive set of continuous full 3D VDF measurements at 1 s cadence has been obtained in 2025. More recently, we have fully restored the PAS burst mode. Since December 2025, PAS is then operated at a continuous 1 s cadence, with 8 bursts of 5 minutes per day during which full 3D measurements at 2 or 4 Hz, thus below the proton cyclotron period, are performed. As illustrated by examples (waves, sharp gradients, turbulence, shocks), this obviously re-opens a window to study various dynamical plasma phenomena at ion kinetic scales.
How to cite: Louarn, P., Fedorov, A., Barthe, A., Penou, E., Génot, V., Fargette, N., Kieokaew, R., Plotnikov, I., Réville, V., Rouillard, A., Lavraud, B., Prech, L., D'Amicis, R., Raines, J. M., Lewis, G., and Owen, C. J.: The Solar Wind at ‘short scales’: Observations at second and sub-second cadences with PAS/SWA. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21760, https://doi.org/10.5194/egusphere-egu26-21760, 2026.
Abundance ratios of heavy ions in the solar wind can be used to probe the low solar corona through the freeze-in and First Ionization Potential (FIP) effects, while their speeds and temperatures can probe both collisionless and collisional processes in the solar wind. We present results demonstrating how heavy ion properties act as diagnostics for phenomena spanning different regimes within the heliosphere. Through a cross-correlation analysis between heavy ion density ratios and proton specific entropy from 1998-2011, we find that the variability in solar wind fluid entropy freezes-in between approximately 1.4-1.8 solar radii in heliocentric distance, constraining time-dependent processes in solar wind formation. Additionally, by incorporating proton temperature anisotropies to compare with heavy ion temperatures, we observe that certain heavy ion species are less subject to the CGL conditions in the highly collisionless solar wind than protons are, placing constraints on inter-species energy partitioning. These analyses, based on measurements of heavy ions at 1 AU, can be extended to data collected by the Heavy Ion Sensor onboard Solar Orbiter. Through the incorporation of proton anisotropies and heavy ion measurements across variable heliocentric distances, these extended analyses will further probe the thermodynamic evolution of the solar wind.
How to cite: Nakhleh, A., Viall, N., Lepri, S., and Raines, J.: Heavy Ion Properties as Diagnostics of Solar Wind Thermodynamic Evolution, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22023, https://doi.org/10.5194/egusphere-egu26-22023, 2026.
Particles in the solar wind show a variety of deviations from thermodynamic equilibrium. These non-thermal features include secondary particle beams drifting relative to the main core population. Several mechanisms have been proposed to explain the formation of such beams, but the topic remains debated.
Recently, thanks to the excellent energy resolution of the Proton Alpha Sensor (PAS) on board Solar Orbiter, the technique described in De Marco et al. (A&A, 2023) has made it possible, in many cases, to clearly identify, not only proton beam, but also the more elusive alpha-particle beam. In this preliminary work, we present observations in which the proton velocity distribution function, instead of following a simple core+beam scenario, displays a more complex structure, exhibiting modulations consistent with the superposition of several sub-populations. Such multi-beam configurations are typically short-lived, representing transient stages in the evolution of proton beams. These observations indicate that proton populations may be continuously reshaped by local kinetic processes, providing an observational basis for future studies on the formation and evolution of multiple proton populations. Furthermore, these complex distributions can offer valuable insight into wave–particle interactions in the solar wind, helping to connect kinetic-scale structures with plasma turbulence and instabilities.
How to cite: De Marco, R., Dhamane, O. S., D'Amicis, R., Benella, S., Perrone, D., and Bruno, R.: Observations of multiple ion populations in solar wind velocity distributions with Solar Orbiter-PAS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13538, https://doi.org/10.5194/egusphere-egu26-13538, 2026.
Interplanetary (IP) shock waves are one of the direct manifestations of solar activity impacting the normal state of the solar wind as it moves through the heliosphere. In the heliosphere, shocks can occur individually or in linked pairs. Linked shock pairs manifest as two successive compression fronts in the plasma, typically travelling in the same direction, but originating from different sources. One such source of paired shocks are corotating interaction regions (CIRs), where the fast solar wind from the coronal hole overtakes the slower solar wind. When that happens, the interaction creates compression regions at the boundaries of the solar wind flux, leading to sudden changes in its parameters and resulting in the formation of forward and reverse shocks.
Another source of the formation of paired shock waves are coronal mass ejections (CMEs) that occur in various active regions (ARs), or sequential CMEs from the same ARs. Paired shock waves are an effective accelerator of energetic charged particles, which are fundamental to heliospheric dynamics. They also play a key role in modulating cosmic rays and triggering geomagnetic disturbances in the near-Earth space.
Our study examines the main characteristics of the forward and reverse shock pair detected on May 21, 2024, when Solar Orbiter flew at a distance of 0.79 AU from the Sun, and about 170 degrees west of the Earth-Sun line. We discuss CMEs as sources of the shock pair, and present the main parameters of the forward and reverse shocks in the interaction region. The study is based on experimental data regarding the kinetic parameters of the solar wind and characteristics of the interplanetary magnetic field, as derived from instruments on the Solar Orbiter mission. We also discuss an abrupt increase in energetic ion fluxes within the interaction region of both shocks, as recorded by the Energetic Particle Detector (EPD) onboard the Solar Orbiter mission.
This work is supported by the “Long-term program of support of the Ukrainian research teams at the Polish Academy of Sciences carried out in collaboration with the U.S. National Academy of Sciences with the financial support of external partners”.
How to cite: Yakovlev, O., Dudnik, O., Mason, G., Dudnik, B., Warmuth, A., Schuller, F., and Wimmer-Schweingruber, R. F.: Case study of the forward-reverse interplanetary shock wave pair in May 2024, detected by Solar Orbiter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-435, https://doi.org/10.5194/egusphere-egu26-435, 2026.
High-energy electrons in the heliosphere are significantly influenced by irregularities in the solar wind and interplanetary magnetic field. One of the most powerful and actively studied irregularities are interplanetary (IP) shocks. We used data from Solar Orbiter’s Solar Wind Analyser (SWA) and magnetometer (MAG), and the method developed by Yakovlev et al. (2025) to determine the relevant shock parameters. We identified 69 IP shocks which occurred at varying distances from the Sun.
To demonstrate the variability in acceleration, dissipation, and absence of response of high-energy electrons across selected narrow energy bands, we analyzed data derived from the Suprathermal Telescope of Electrons and Protons (STEP), the Electron and Proton Telescope (EPT, Sun direction), and the High Energy Telescope (HET, Sun direction) of the Energetic Particle Detector (EPD) suite onboard Solar Orbiter. For a quick-look analysis, we demonstrate light curves of particle fluxes in a few energy ranges in the upstream/foreshock and downstream/aftershock regions.
We also present selected parameters of the IP shock wave, including IP shock types (FF, SR, SF, FR), magnetic and gas compression factors, plasma beta parameters, shock angles, Alfvenic and magnetosonic Mach numbers, as well as Alfvenic and shock speeds.
This work is supported by the “Long-term program of support of the Ukrainian research teams at the Polish Academy of Sciences, carried out in collaboration with the U.S. National Academy of Sciences, with the financial support of external partners”.
1. O. Yakovlev, O. Dudnik, A. Wawrzaszek. Statistical analysis of interplanetary shock waves measured by a Solar Wind Analyzer and a magnetometer onboard the Solar Orbiter Mission in 2023. Journal of Space Weather and Space Climate. 2025, 15, 32. https://doi.org/10.1051/swsc/2025027
How to cite: Dudnik, O., Yakovlev, O., Dudnik, B., Mason, G., Warmuth, A., Schuller, F., and Wimmer-Schweingruber, R. F.: Responses of energetic electrons to the interplanetary shock waves detected in 2024 with Solar Orbiter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-363, https://doi.org/10.5194/egusphere-egu26-363, 2026.
The BepiColombo Environmental Radiation Monitor (BERM), currently travelling toward Mercury, and the Energetic Particle Detector (EPD) aboard Solar Orbiter are both monitoring the radiation environment in the inner heliosphere. Three Solar Energetic Particle (SEP) events, 2021-07-15, 2022-07-23 and 2023-03-13 were detected simultaneously by the two missions during intervals of favourable magnetic connectivity, providing valuable cases for comparative analysis and instrument intercalibration.
We investigated the interplanetary conditions of each event using solar wind plasma and magnetic field observations. Proton anisotropy measurements from Solar Orbiter enabled the identification of isotropic periods during the decay phase of the SEP events, from which representative proton spectra were derived. These spectra were then fitted and compared with BERM observations to obtain intercalibration factors.
Our results confirm a high level of agreement between the instruments. For the 2.15 MeV and 6.85 MeV proton channels, we obtained calibration factors of 0.95±0.10 and 1.02±0.30, corresponding to deviations of only 5% and 2%. These findings demonstrate the consistency of SEP measurements by BERM and EPD and highlight the valuable role that planetary missions can play in heliophysics research.
How to cite: Gomes, A., Rodríguez-García, L., Pinto, M., Gómez-Herrero, R., Rodríguez-Pacheco, J., Wimmer-Schweingruber, R., Jones, G., Besse, S., and Gonçalves, P.: Intercalibration between energetic particle instruments BERM onboard BepiColombo and EPD aboard Solar Orbiter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-723, https://doi.org/10.5194/egusphere-egu26-723, 2026.
The Sun is the most efficient particle accelerator in the solar system, capable of accelerating particles such as electrons and protons to relativistic energies. Solar Energetic Particles (SEPs) are known to be accelerated both at solar flare reconnection sites and by shocks driven by coronal mass ejections. One way to distinguish between these two SEP acceleration mechanisms is through their energy spectra, either fluence or peak intensity.
While the spectral breaks commonly observed in solar energetic electron (SEE) spectra may represent signatures of the acceleration process, several transport-related effects have also been proposed as their origin. In this study, we analyse the energy spectra of intense SEE events measured by Solar Orbiter’s Energetic Particle Detector (EPD) between December 2020 and December 2022. EPD’s unprecedented energy resolution enables us to identify spectral features with greater detail than previously possible.
We investigate the shape of SEE spectra by fitting them with a range of mathematical models. Our results are compared with previous studies, and we explore possible connections to transport-related effects. In addition, we examine potential correlations between spectral features and parameters such as radial distance or properties of the associated solar events.
Our analysis reveals four distinct spectral shapes: single power-law, double power-law, and two types of triple power-law spectra, namely knee–knee (KK) and ankle–knee (AK) forms. No significant correlations with radial distance are found. However, the observed spectral shapes exhibit an ordering with respect to the longitudinal separation between the spacecraft and the associated solar flare.
We conclude that multiple processes likely contribute to shaping SEE spectra. Our results suggest that the two breaks observed in KK triple power-law spectra arise from distinct physical effects, namely Langmuir-wave generation and pitch-angle scattering. Furthermore, the break in double power-law spectra may represent a merger of the first and second breaks seen in KK triple power-law spectra.
How to cite: Fedeli, A., Dresing, N., Gieseler, J., Warmuth, A., Schuller, F., Gómez-Herrero, R., Jebaraj, I. C., Espinosa, F., and Vainio, R.: Peak-intensity energy spectra of intense solar energetic electron events measured with Solar Orbiter in 2020-2022, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6758, https://doi.org/10.5194/egusphere-egu26-6758, 2026.
Solar Orbiter is able to cover the far-side of the Sun for almost 6 months every year. This allows us to detect far-side flux emergence or disappearance events that remain undetected at Earth for several days. We showed in a previous study that these events, although located on the other side of the Sun, can affect the modeling of the Sun-Earth chain and change space weather previsions (Perri et al. 2024).
Our aim is to scan Solar Orbiter/PHI data in order to provide a catalogue of the major far-side events undetected at Earth.
We scan data for the period 2022-2024, and for each year we look at the data between March and September where the far-side coverage is the best. We combine SO/PHI maps with SDO/HMI, and compare them with GONG-ADAPT synoptic maps used in space weather forecasts. We use a specific post-processing in order to make the data comparable, and find criteria and thresholds to help us detect major differences between day-side and far-side magnetic fields.
We find a list of 27 true flux-emergence events, and an additional list of 3 events where a decaying active region actually regained an intense magnetic field. The delay between the far-side and the Earth field of view detection ranges from 2 to 15 days, with a peak at 12. All these far-side emergence events take place at low latitudes (between -25 and 30) due to the fact that we are at the beginning of solar cycle 25. However, they appear at all longitudes (no active longitude for this kind of events). They all show a similar size (about 10 degrees in both latitudinal and longitudinal extent). We compare these observations with far-side maps from both GONG and HMI websites, and find an average delay of 4 days for the detection for HMI, and 7 days for GONG.
This catalogue can be used to improve space weather forecasts, and shows the need for synchronic views of the Sun.
How to cite: Perri, B., Legrand, H., Brun, A. S., Finley, A., and Strugarek, A.: Far-side active region emergence catalogue from Solar Orbiter/PHI, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7581, https://doi.org/10.5194/egusphere-egu26-7581, 2026.
Forbush decreases (FDs) are one of the very common in-situ signatures of interplanetary coronal mass ejections (ICMEs) throughout the heliosphere. These short-term reductions in the galactic cosmic ray flux are measured by ground-based instruments at Earth and Mars, as well as various spacecraft throughout the heliosphere (most recently by Solar Orbiter). We recently developed an analytical model to explain CME-related FDs using an expansion-diffusion approach and utilized it to develop a best-fit procedure (ForbMod, Dumbovic et al., 2024). According to the model, the amplitude of the depression at a given point in the heliosphere depends on the initial CME properties as well as its evolutionary properties.
We develop a scheme that will allow us to analyze CME evolution using a set of CME-ICME-FD observations, as well as in situ measurements only, and design a graphical user interface to perform ICME and FD analysis throughout the heliosphere. We measure, catalogue and analyse ICMEs and related FDs using Helios, Ulysess, SOHO and Solar Orbiter spacecraft, as well as ground-based measurements from the South Pole neutron monitor at Earth and MSL/RAD at Mars. This research was partly funded by the European Space Agency (projects ForbMod and ForbMod2) and partly by European Union (project SPEARHEAD, No 101135044). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Health and Digital Executive Agency (HaDEA). Neither the European Union nor the granting authority can be held responsible for them.
How to cite: Dumbovic, M., Bernd, H., Malte, H., Marlon, K., Athanasios, P., Alexander, M., Ilya, U., Jan, G., Erika, P., Akhay Kumar, R., Galina, C., and Anamarija, K.: Measuring Forbush decreases and probing CME evolution throughout the heliosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18496, https://doi.org/10.5194/egusphere-egu26-18496, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 4
EGU26-5972 | Posters virtual | VPS28
Solar Orbiter observations of the largest ground level enhancement of Solar Cycle 25 to date (GLE 77)Thu, 07 May, 14:03–14:06 (CEST) vPoster spot 4