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Accession Number:
ADA561741
Title:
A Comparison of Ground Level Event e/p and Fe/O Ratios with Associated Solar Flare and CME Characteristics (Postprint)
Descriptive Note:
Technical paper, 1 Oct 2007-15 Apr 2011
Corporate Author:
AIR FORCE RESEARCH LAB KIRTLAND AFB NM SPACE VEHICLES DIRECTORATE
Report Date:
2012-03-06
Pagination or Media Count:
22.0
Abstract:
Solar energetic particle SEP events reaching rigidities 1 GV are observed at 1 AU as ground-level events GLEs. They are considered to be extreme cases of gradual SEP events, produced by shocks driven by wide and fast CMEs that are usually associated with long-duration 1 hour soft X-ray SXR flares. However, some large gradual SEP events, including GLEs, are associated with flares of short-duration 1 hour timescales comparable to those of flares seen with impulsive, low-energy SEP events with enhanced charge states, heavy-element abundances, and ep ratios. The association of some GLEs with short-duration SXR events challenges us to understand the GLE event-to-event variation with SXR durations and whether it truly reflects the nature of the particle acceleration processes or simply the characteristics of the solar regions from which large, fast CMEs arise. We examine statistically the associated flare, active region AR, and CME characteristics of 40 GLEs observed since 1976 to determine how the GLE ep and FeO ratios, each measured in two energy ranges, depend on those characteristics. The abundance ratios trend weakly to lower, more coronal, and less scattered values with increasing flare timescales, thermal and nonthermal peak fluxes, and measures of source AR sizes. These results and the wide range of solar longitude connections for GLEs with high abundance ratios argue against a significant role for flare effects in the GLEs. We suggest that GLE SEPs are accelerated predominately in CME-driven shocks and that a coupling of flare size and timescales with CME properties could explain the SEP abundance correlations with flare properties.
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
