The Origin of Energetic Solar Protons: Comparative Analysis of Ground-level Enhancement (GLE) Events and Non-GLE Solar Energetic Particle Events

This study explores the acceleration origins of solar energetic particles (SEPs) by analyzing the energy spectral characteristics of particles in ground-level enhancement (GLE) events and common SEP (non-GLE) events, as well as the correlations of the peak intensities of energetic particles with flare and coronal mass ejection (CME) diagnostic parameters. By examining the peak energy spectra of protons, for protons with energies >66 MeV, the peak intensities in most GLE events are significantly higher than those in SEP events, establishing an energy threshold distinguishing GLE from non-GLE events. Given the strong correlation between energetic electrons and protons, radio bursts and soft X-rays (SXRs) produced by energetic electrons can be used to study acceleration regions of GLE. Based on data from solar cycles 23 and 24, multifrequency radio data (5, 8.8, and 15.4 GHz) and SXR intensity analysis reveal the heights of particle acceleration. The results indicate that protons with energies >66 MeV in GLE events are closely associated with flare-related acceleration in the low corona, although a contribution from CME-driven shock acceleration cannot be excluded. In contrast, lower-energy protons (<10 MeV) are primarily accelerated by CME-driven shocks. Moreover, SEPs at intermediate energies exhibit a mixed origin, which includes particles accelerated by both flares and CME-driven shocks. These findings provide key insights into the mechanisms of particle acceleration in solar events.