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Published 2009 | Published
Book Section - Chapter Open

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


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.

Additional Information

This work was supported by NASA at Caltech under grants NNX8AI11G and NNX06AC21G, and under subcontract SA2715-26309 from UC Berkeley under NASA contract NAS5-03131. We appreciate the availability of GOES data at the NOAA website and thank Allan Tylka for advice on HEPAD data. Finally, we thank Eileen Chollet for her assistance with this paper.

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October 23, 2023