Abstract Occasionally, solar energetic particle (SEP) events associated with fast, wide coronal mass ejections (CMEs) driving interplanetary shocks exhibit Fe/O abundance ratios that are significantly higher than the nominal value of 0.134. The cause of this enrichment in Fe remains unclear, but there are two prevailing theories: contribution from flare-accelerated material, and reacceleration of suprathermal remnant flare material by a quasiperpendicular shock. The 2024 July 23 SEP event was observed by four spacecraft spread over ∼160° of solar longitude and 0.4 au in radial distance. We examine the H, He, O, and Fe spectra and He/H and Fe/O abundance ratios observed at each spacecraft, and find that three measured Fe/O ratios >0.6 were relatively independent of energy. The fourth spacecraft measured strongly energy-dependent Fe/O ratios reaching very low values of 0.02 at a few MeV nuc −1 . In an effort to evaluate the plausibility of the two explanations for Fe-rich SEP events, we studied the magnetic connection of the spacecraft to the solar source and the evolving CME; the velocity dispersion of the first arriving particles; and the time evolution of the Fe/O ratios. We also noted the pre-event CME and flare activity. We find that neither scenario is clearly consistent with the compositional variations between the four spacecraft, but more detailed modeling of the magnetic connections between the spacecraft and the solar source and the propagating shock may be beneficial.
Cohen et al. (Thu,) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: