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Energy Spectra, Composition, and Other Properties of Ground-Level Events During Solar Cycle 23

Mewaldt, R. A. and Looper, M. D. and Cohen, C. M. S. and Haggerty, D. K. and Labrador, A. W. and Leske, R. A. and Mason, G. M. and Mazur, J. E. and von Rosenvinge, T. T. (2012) Energy Spectra, Composition, and Other Properties of Ground-Level Events During Solar Cycle 23. Space Science Reviews, 171 (1-4). pp. 97-120. ISSN 0038-6308.

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We 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, SAMPEX, and STEREO spacecraft and extend from ∼0.1 to ∼500–700 MeV. All of the proton spectra exhibit spectral breaks at energies ranging from ∼2 to ∼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 >40 MeV/nuc. In the energy range 45 to 80 MeV/nucleon about ∼50 % of GLE events have properties in common with impulsive ^(3)He-rich SEP events, including enrichments in Ne/O, Fe/O, ^(22)Ne/^(20)Ne, and elevated mean charge states of Fe. These ^(3)He-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_(Fe)>≈+20 if the acceleration starts at ∼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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Mewaldt, R. A.0000-0003-2178-9111
Cohen, C. M. S.0000-0002-0978-8127
Haggerty, D. K.0000-0001-6395-8943
Labrador, A. W.0000-0001-9178-5349
Leske, R. A.0000-0002-0156-2414
Mason, G. M.0000-0003-2169-9618
Additional Information:© 2012 Springer Science+Business Media B.V. Received: 14 February 2011; Accepted: 18 April 2012; Published online: 30 May 2012. 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, SOHO CME data at the Catholic University website, and thank Allan Tylka for advice on using HEPAD data. We are grateful for helpful suggestions from both reviewers. Finally, we thank Nat Gopalswamy and Nariaki Nitta for helpful discussions, for organizing the two LWS workshops on GLEs, and for serving as editors for this volume.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
University of California, BerkeleySA2715-26309
Subject Keywords:Sun: particle emission; Sun: coronal mass ejections (CMEs); Acceleration of particles; Solar energetic particle acceleration; Sun: composition; Ionic charge states
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2012-15
Issue or Number:1-4
Record Number:CaltechAUTHORS:20121109-100850749
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35382
Deposited By: Jason Perez
Deposited On:09 Nov 2012 19:32
Last Modified:09 Mar 2020 13:18

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