- 1National Observatory of Athens, IAASARS, Penteli, Greece (atpapaio@astro.noa.gr)
- *A full list of authors appears at the end of the abstract
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).
Co-authors: Laura Rodríguez-García (2,3), Raúl Gómez-Herrero (3), Eleni Lavasa (1,4), Athanasios Kouloumvakos (5), George Vasalos (1), Alexander Warmuth (6), Ian G. Richardson (7,8), David Lario (8), Ioannis Zouganelis (2), Bernd Heber (9), Marlon Köberle (9), Manon Jarry (1), Monica Laurenza (10), Francisco Espinosa Lara (3), Ignacio Cernuda (3), Patrick Kühl (8), Jan Gieseler (11), Christian Palmroos (11), Frederic Schuller (6), Krzysztof Barczynski (12,13), Sebastian Fleth (9), Anastasios Anastasiadis (1), Andrew Walsh (2), Daniel Müller (14), Javier Rodríguez-Pacheco (3), Robert F. Wimmer-Schweingruber (9), Rami Vainio (11), and Alexis P. Rouillard (15) Affiliations: (2) European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain, (3) Universidad de Alcalá, Space Research Group, 28805 Alcalá de Henares, Spain, (4) National & Kapodistrian University of Athens, Athens, Greece, (5) The Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Road, Laurel, MD 20723, USA, (6) Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany, (7) NASA Goddard Space Flight Center, Heliophysics Science Division, Greenbelt, MD 20771, USA, (8) Department of Astronomy, University of Maryland, College Park, MD 20742, USA, (9) Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24118 Kiel, Germany, (10) INAF-Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, I-00133,Rome, Italy, (11) Department of Physics and Astronomy, University of Turku, 20500 Turku, Finland, (12) ETH-Zurich, Hönggerberg campus, HIT building, Zürich, Switzerland, (13) PMOD/WRC, Dorfstrasse 33, 7260 Davos Dorf, Switzerland, (14) European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands, (15) IRAP, Université Toulouse III—Paul Sabatier, CNRS, CNES, Toulouse, France
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.
