The Influence of Coronal Mass Ejection Characteristics on the Spread of Solar Energetic Particles
2019 July 22
A study of 41 large, multi-spacecraft solar energetic particle (SEP) events observed by ACE and STEREO revealed large variability in the longitudinal spread of SEPs. By examining the longitudinal widths determined using observations of H, He, O, and Fe it was found that the widths exhibited no systematic charge-to-mass (Q/M) dependence. However, a dependence on energy was identified with higher energies (10 MeV/n) exhibiting narrower distributions than lower energies (0.3 MeV/n). Here we investigate the influence of the characteristics of the associated coronal mass ejection (CME) on the widths of the SEP longitudinal spread. In particular, we examine the speed, mass, kinetic energy, and acceleration of the relevant CMEs and the distributions of H, He, O, and Fe at 0.3, 1 and 10 MeV/n. A weak correlation between the SEP longitudinal spreads at 10 MeV/n and CME speed is found for events observed by three-spacecraft; a similar correlation with kinetic energy may be related. The observed correlation with CME acceleration is largely due to one event with narrow width and large deceleration. A comparison of properties for CMEs associated with two- and three-spacecraft events reveals significant differences. The three-spacecraft events have CMEs that, on average, are 50% faster and more massive, have three times the kinetic energy, but decelerate at a rate almost six times those of the two-spacecraft events.