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Heavy-ion elemental abundances in large solar energetic particle events and their implications for the seed population

Desai, M. I. and Mason, G. M. and Gold, R. E. and Krimigis, S. M. and Cohen, C. M. S. and Mewaldt, R. A. and Mazur, J. E. and Dwyer, J. R. (2006) Heavy-ion elemental abundances in large solar energetic particle events and their implications for the seed population. Astrophysical Journal, 649 (1). pp. 470-489. ISSN 0004-637X.

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We have surveyed the ~0.1–10 MeV nucleon to the -1 abundances of heavy ions from 3He through Fe in 64 large solar energetic particle (LSEP) events observed on board the Advanced Composition Explorer from 1997 November through 2005 January. Our main results are (1) the 0.5–2.0 MeV nucleon to the -1 3He/ 4He ratio is enhanced between factors of ~2–150 over the solar wind value in 29 (~46%) events. (2) The Fe/O ratio in most LSEP events decreases with increasing energy up to ~60 MeV nucleon to the -1. (3) The Fe/O ratio is independent of CME speed, flare longitude, event size, the 3He/4He ratio, the pre-event Fe/O ratio, and solar activity. (4) The LSEP abundances exhibit unsystematic behavior as a function of M/Q ratio when compared with average solar wind values. (5) The survey-averaged abundances are enhanced with increasing M/Q ratio when compared with quiet coronal values and with average gradual SEP abundances obtained at 5–12 MeV nucleon to the -1. (6) The event-to-event variations in LSEP events are remarkably similar to those seen in CME-driven IP shocks and in 3He-rich SEP events. The above results cannot be explained by simply invoking the current paradigm for large gradual SEP events, i.e., that CME-driven shocks accelerate a seed population dominated by ambient coronal or solar wind ions. Instead, we suggest that the systematic M/Q-dependent enhancements in LSEP events are an inherent property of a highly variable suprathermal seed population, most of which is accelerated by mechanisms that produce heavy-ion abundances similar to those observed in impulsive SEP events. This heavy-ion-enriched material is subsequently accelerated at CME-driven shocks near the Sun by processes in which ions with higher M/Q ratios are accelerated less efficiently, thus causing the Fe/O ratios to decrease with increasing energy.

Item Type:Article
Related URLs:
URLURL TypeDescription
Desai, M. I.0000-0002-7318-6008
Mason, G. M.0000-0003-2169-9618
Krimigis, S. M.0000-0003-2781-2386
Cohen, C. M. S.0000-0002-0978-8127
Mewaldt, R. A.0000-0003-2178-9111
Additional Information:© 2006 The American Astronomical Society. Received 2006 February 13; accepted 2006 May 4. We are grateful to the members of the Space Physics Group, University of Maryland and the Johns Hopkins Applied Physics Laboratory (JHU/APL) for the construction of the ULEIS instrument. Work at the University of Maryland was supported by NASA contract NAS5-30927 and NASA grant PC 251428; work at Southwest Research Institute was partially supported by NASA grant NNG05GQ94G and NSF grant ATM 05-55878; work at JHU/APL was supported by NASA grant NNG04GJ51G. Work at the California Institute of Technology was supported by NASA grants NAG5-12929 and NNG05GQ94G and NSF grant ATM 04-54428. We acknowledge the use of the lists of Solar Proton Events Affecting the Earth Environment provided by the NOAA Space Environment Services Center at and that of CMEs provided by the SOHO LASCO team at
Group:Space Radiation Laboratory
Funding AgencyGrant Number
NASAPC 251428
Subject Keywords:Sun: particle emission
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Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2006-06
Issue or Number:1
Record Number:CaltechAUTHORS:DESapj06
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5744
Deposited By: Lindsay Cleary
Deposited On:31 Oct 2006
Last Modified:09 Mar 2020 13:18

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