He/H Ratio in Solar Energetic Particle Events

One complicating factor in predicting the variability of gradual solar energetic particles is the potential influence of a seed particle population. Numerous observations suggest that the source of this seed population is the suprathermal tail with ion energies between 1.5-2 times the bulk solar wind and ~100 keV/nuc. However, studies have also shown that the SEP source population is consistent with the ambient coronal thermal (T ~ 1.5 MK) ions with energies ~ 100 eV. Kahler et al. 2021 recently examined the He/H ratio for gradual events during solar cycle 23 and 24 and determined a correlation between the He/H ratio of gradual SEP events and that of the ambient solar wind, suggesting a connection between solar wind ions and the seed population of SEPs. On 2021 April 17, a gradual SEP event was detected by the Integrated Science Investigation of the Sun (IS☉IS) instrument suite on Parker Solar Probe (PSP) when the spacecraft was inside of 0.4 au.We discuss this event in the context of the solar wind environment at 0.4 au and examine other events well within 1 AU from PSP.