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| Titel |
Systematic Charge-to-Mass-Dependence of Heavy Ion Spectral Breaks in Large Gradual Solar Energetic Particle Events |
| VerfasserIn |
Mihir Desai, Glenn Mason, Robert Ebert, Maher Dayeh, David McComas, Gang Li, Richard Mewaldt, Christina Cohen, Nathan Schwadron, Charles Snith |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250123030
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| Publikation (Nr.) |
 EGU/EGU2016-2199.pdf |
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| Zusammenfassung |
| We fit the ∼0.1-500 MeV nucleon−1 H-Fe spectra in 46 large SEP events surveyed by Desai
et al. (2015) with the double power-law Band function to obtain a normalization constant,
low- and high-energy Band parameters γaand γb; and spectral break energy EB. We also
calculate the low-energy power-law spectral slope γ1. Our results are: 1) γa, γ1, andγb are
species-independent and the spectra steepen with increasing energy; 2) the low-energy
power-law spectral slopes γ1are consistent with diffusive acceleration at shocks with
compression ratios between ∼2 – 4 as predicted by Schwadron et al. (2015); 3) the
spectral breaks EB’s are well ordered by Q/M ratio, and decrease systematically with
decreasing Q/M, scaling as (Q/M)α with α in most events varying between ∼0.2-2, as
predicted by Li et al (2009); 4) α is well correlated with Fe/O at ∼0.16-0.23 MeV
nucleon−1, but not with the ∼15-21 MeV nucleon−1 Fe/O and the ∼0.5-2.0 MeV
nucleon−1 3He/4He ratios; 5) In most events: α <1.4, the spectra steepen significantly at
higher energy with γb–γa >3, and O EB increases with γb–γa; and 6) Many extreme
events (associated with faster CMEs and GLEs) are Fe-rich and 3He-rich, have
large α ≥1.4, flatter spectra at low and high energies with γb–γa <3, and EB that
anti-correlates with γb–γa. In most events, the Q/M-dependence of EB is consistent
with the equal diffusion coefficient condition, while the event-to-event variations in
α may be driven by differences in the near-shock wave intensity spectra, which
are flatter than the Kolmogorov turbulence spectrum but weaker when compared
to extreme events. We interpret these results as being due to weaker turbulence
that allows the SEPs to easily escape, resulting in weaker Q/M-dependence of EB,
lower α values, and spectral steepening at higher energies. In contrast for extreme
events, the stronger Q/M-dependence of EB, larger α values, and harder spectra
at high and low energy occur because enhanced wave power enables faster CME
shocks to accelerate flare suprathermals more efficiently than ambient coronal ions. |
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