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Energy Spectra, Composition, and Other Properties of Ground-Level Events During Solar Cycle 23We report spacecraft measurements of the energy spectra of solar protons and other solar energetic particle properties during the 16 Ground Level Events (GLEs) of Solar Cycle 23. The measurements were made by eight instruments on the ACE, GOES, SAMPBX, and STEREO spacecraft and extend from approximately 0.1 to approximately 500-700 MeV. All of the proton spectra exhibit spectral breaks at energies ranging from approximately 2 to approximately 46 MeV and all are well fit by a double power-law shape. A comparison of GLE events with a larger sample of other solar energetic particle (SEP) events shows that the typical spectral indices are harder in GLE events, with a mean slope of -3.18 at greater than 40 MeV/nuc. In the energy range 45 to 80 MeV/nucleon about approximately 50% of GLE events have properties in common with impulsive He-3-rich SEP events, including enrichments in Ne/O, Fe/O, Ne-22/Ne-20, and elevated mean charge states of Fe. These He-3 rich events contribute to the seed population accelerated by CME-driven shocks. An analysis is presented of whether highly-ionized Fe ions observed in five events could be due to electron stripping during shock acceleration in the low corona. Making use of stripping calculations by others and a coronal density model, we can account for events with mean Fe charge states of (Q(sub Fe) is approximately equal to +20 if the acceleration starts at approximately 1.24-1.6 solar radii, consistent with recent comparisons of CME trajectories and type-II radio bursts. In addition, we suggest that gradual stripping of remnant ions from earlier large SEP events may also contribute a highly-ionized suprathermal seed population. We also discuss how observed SEP spectral slopes relate to the energetics of particle acceleration in GLE and other large SEP events.
Document ID
20120016495
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Mewaldt, R. A.
(California Inst. of Tech. Pasadena, CA, United States)
COhen, C. M. S.
(California Inst. of Tech. Pasadena, CA, United States)
Labrador, A. W.
(California Inst. of Tech. Pasadena, CA, United States)
Leske, R. A.
(California Inst. of Tech. Pasadena, CA, United States)
Looper, M. D.
(Aerospace Corp. Los Angeles, CA, United States)
Haggerty, D. K.
(Johns Hopkins Univ. Laurel, MD, United States)
Mason, G. M.
(Johns Hopkins Univ. Laurel, MD, United States)
Mazur, J. E.
(Aerospace Corp. Chantilly, VA, United States)
vonRosenvinge, T. T.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 26, 2013
Publication Date
April 18, 2012
Publication Information
Publication: Space Science Reviews
Volume: 171
Issue: 4-Jan
Subject Category
Astrophysics
Report/Patent Number
GSFC.JA.7381.2012
Funding Number(s)
CONTRACT_GRANT: NNX06AC21G
CONTRACT_GRANT: SA2715-26309
CONTRACT_GRANT: NNX8AI11G
CONTRACT_GRANT: NAS5-03131
Distribution Limits
Public
Copyright
Other

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