Proton acceleration by CME-driven shock during the 21 November 2024 (GLE76) event

On 21 November 2024, a strong solar energetic particle (SEP) event implying protons of 100 MeV near Earth was associated with an eruption located on the far side of the Sun as viewed from Earth.
The source region was identified using EUV observations from the Solar-Terrestrial Relations Observatory (STEREO) as NOAA AR 13892, located around (lon, lat) = (355°, -20°) in Carrington coordinates at around 00:45 UT. Due to its location, the associated flare produced only weak soft X-ray signatures in Earth-based observations. The Spectrometer/Telescope for Imaging X-rays (STIX) instrument on-board Solar Orbiter, which was also positioned on the far side relative to the parent active region, recorded an increase in the 15-25 keV range.
The flare was followed by a coronal mass ejection (CME) of speed 1436 km/s, propagating on the solar limb and driving a shock wave at its front. The 3D geometry of the CME-driven shock was reconstructed using white-light remote-sensing observations from STEREO-A and SOHO. This was then combined with global magneto-hydrodynamic (MHD) simulations from Predictive Science Inc. (PSI), to derive the MHD properties of the shock surface, as well as the magnetic field lines connecting the spacecraft to the Sun’s surface.
This enables the study of MHD shock parameters evolution along field lines regarding the SEP profile and characteristics measured at the corresponding spacecraft. We therefore investigated acceleration scenarios for the energetic particles that reached Earth, STEREO-A and Solar Orbiter, which are magnetically connected to different regions of the evolving shock.