Spectra and Properties of Ground-Level Events During Solar Cycle 23

Abstract

We report spacecraft measurements of the energy spectra of solar protons and other solar particle properties during the 16 Ground Level Events (GLEs) of Solar Cycle 23. The measurements were made by seven instruments on the ACE, GOES, SAMPEX, and STEREO spacecraft and extend from »0.1 to »700 MeV. All of the proton spectra exhibit spectral breaks at energies ranging from »2.4 to »33 MeV and all are well fit by a double power-law shape. A comparison of GLE events with a sample of other SEP events shows that GLEs typically have harder spectra, with a mean slope of -3.17 at >40 MeV/nuc. On average, GLE events are enriched in species associated with impulsive _3He-rich SEP events, including enrichments in Ne/O, Fe/O, ^(22)Ne/^(20)Ne, and elevated mean charge states of Fe. This paper discusses these and other properties of particles measured in situ in GLE events.