Fig. 28

Possible reconciliation between the two-class paradigm of the early 1900s and the puzzling SEP observations from Wind, ACE, and STEREO. The SEPs are grouped into four sub-classes according to their acceleration locations and the contributions of relevant physical processes (taken from Reames 2020). a Elements experience different FIP processing on open and closed field lines. b SEPs are accelerated in magnetic reconnection regions or by CME shocks. c SEPs enriched in ³He and heavy ions escape along open field lines associated with solar jets, and not from closed field lines associated with solar flares. d Weaker CME-driven shocks preferentially accelerate residual suprathermal material left over from multiple jets, while the stronger CME shocks accelerate ambient coronal material. e Fast CMEs associated with jets also accelerate suprathermal jet-accelerated material. f Rigidity-dependent trapping near CME shocks or scattering in the corona and the IP medium modifies heavy ion abundances and energy spectra in large gradual SEP events. In some large events, self-generated waves can enhance particle trapping and increase the acceleration efficiencies of the CME shocks