Influence of Large-scale Interplanetary Structures on the Propagation of Solar Energetic Particles: The Multispacecraft Event on 2021 October 9

• Published in: The Astrophysical journal 2022-07, Vol.934 (1), p.55
• Main Authors: Lario, D., Wijsen, N., Kwon, R. Y., Sánchez-Cano, B., Richardson, I. G., Pacheco, D., Palmerio, E., Stevens, M. L., Szabo, A., Heyner, D., Dresing, N., Gómez-Herrero, R., Carcaboso, F., Aran, A., Afanasiev, A., Vainio, R., Riihonen, E., Poedts, S., Brüden, M., Xu, Z. G., Kollhoff, A.
• Format: Article
• Language: English
• Subjects: Astrophysics; Bepi Colombo (ESA); Coronal mass ejection; Corotating streams; Earth; Energetic particles; Magnetic fields; Protons; Solar coronal mass ejection shocks; Solar energetic particles; Solar Orbiter (ESA); Solar orbits; Solar probes; Solar wind; Spacecraft
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac6efd

An intense solar energetic particle (SEP) event was observed on 2021 October 9 by multiple spacecraft distributed near the ecliptic plane at heliocentric radial distances R ≲ 1 au and within a narrow range of heliolongitudes. A stream interaction region (SIR), sequentially observed by Parker Solar Probe (PSP) at R = 0.76 au and 48° east from Earth ( ϕ = E48°), STEREO-A (at R = 0.96 au, ϕ = E39°), Solar Orbiter (SolO; at R = 0.68 au, ϕ = E15°), BepiColombo (at R = 0.33 au, ϕ = W02°), and near-Earth spacecraft, regulated the observed intensity-time profiles and the anisotropic character of the SEP event. PSP, STEREO-A, and SolO detected strong anisotropies at the onset of the SEP event, which resulted from the fact that PSP and STEREO-A were in the declining-speed region of the solar wind stream responsible for the SIR and from the passage of a steady magnetic field structure by SolO during the onset of the event. By contrast, the intensity-time profiles observed near Earth displayed a delayed onset at proton energies ≳13 MeV and an accumulation of ≲5 MeV protons between the SIR and the shock driven by the parent coronal mass ejection (CME). Even though BepiColombo, STEREO-A, and SolO were nominally connected to the same region of the Sun, the intensity-time profiles at BepiColombo resemble those observed near Earth, with the bulk of low-energy ions also confined between the SIR and the CME-driven shock. This event exemplifies the impact that intervening large-scale interplanetary structures, such as corotating SIRs, have in shaping the properties of SEP events.