Unusually long path length for a nearly scatter-free solar particle event observed by Solar Orbiter at 0.43 au
- 1University of Kiel, Institut für Experimentelle und Angewandte Physik, Kiel, Germany (wimmer@physik.uni-kiel.de)
- 2Universidad de Alcalá, Space Research Group (SRG-UAH), 28801 Alcalá de Henares, Madrid, Spain
- 3Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, USA
- 4Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD 20723, USA
- 5Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
- 6Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
- 7Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium, Ringlaan -3- Av. Circulaire, 1180 Brussels, Belgium
- 8School of Earth and Space Sciences, No. 2 Yifu Building, Peking University, No.5 Yiheyuan Road, Haidian District, Beijing 100871, PR China
- 9National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing (IAASARS), Vas. Pavlou & I. Metaxa, GR-15 236 Penteli, Greece
Solar energetic particles (SEPs) are bound to the interplanetary magnetic field (IMF) by the Lorentz force. The expansion of the IMF close to the Sun focuses the particle pitch-angle distribution, and scattering counteracts this focusing. Solar Orbiter observed an unusual solar particle event on 9 April 2022 when it was at 0.43 astronomical units (au) from the Sun. The inferred IMF along which the SEPs traveled was about three times longer than the nominal length of the Parker spiral.
Nevertheless, the pitch-angle distribution of the particles of this event is highly anisotropic, and the electrons and ions appear to be streaming along the same IMF structures. The angular width of the streaming population is estimated to be approximately 30 degrees. The highly anisotropic ion beam was observed for more than 12 h. This may be due to the low level of fluctuations in the IMF, which in turn is very probably due to this event being inside an interplanetary coronal mass ejection. The slow and small rotation in the IMF suggests a flux-rope structure. Small flux dropouts are associated with very small changes in pitch angle, which may be explained by different flux tubes connecting to different locations in the flare region. The unusually long path length along which the electrons and ions have propagated virtually scatter-free together with the short-term flux dropouts offer excellent opportunities to study the transport of SEPs within interplanetary structures. The 9 April 2022 solar particle event offers an especially rich number of unique observations that can be used to limit SEP transport models.
How to cite: Wimmer-Schweingruber, R. F., Yang, L., Kollhoff, A., Gomez-Herrero, R., Rodriguez-Pacheco, J., Espinosa, F., Cernuda, I., Ho, G. C., Mason, G. M., Warmuth, A., Owen, C. J., Rodriguez, L., Shukhobodskaia, D., Berger, L., Kühl, P., Heber, B., Wang, L., Bucik, R., and Malandraki, O.: Unusually long path length for a nearly scatter-free solar particle event observed by Solar Orbiter at 0.43 au, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2823, https://doi.org/10.5194/egusphere-egu24-2823, 2024.
