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Fe Enhancements in SEP Onsets: Flare/CME Mixture or Transport Effect?

Mason, G. M. and Li, G. and Cohen, C. M. S. and Desai, M. I. and Haggerty, D. K. and Leske, R. A. and Mewaldt, R. A. and Zank, G. P. (2014) Fe Enhancements in SEP Onsets: Flare/CME Mixture or Transport Effect? In: Outstanding Problems in Heliophysics: From Coronal Heating to the Edge of the Heliosphere. Astronomical Society of the Pacific Conference Series. Vol.484. Astronomical Society of the Pacific , San Francisco, CA, pp. 137-144. ISBN 978-1-58381-852-7.

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During the onset phases of SEP events, the Fe/O ratio is often observed to be initially enhanced (˜1) over typical SEP values, followed by a decline to values close to typical averages over entire events (Fe/O ˜0.1). Two mechanisms have been suggested to explain this behavior, namely (1) a two-step process with an initial injection of “flare" particles with high Fe/O followed by shock-accelerated particles with lower Fe/O, and (2) a transport effect wherein the lower charge-to-mass ratio of Fe vs. O results in faster transport of Fe to the observer, leading to enhanced Fe/O in the early stages of the event. Distinguishing between these two scenarios is important to building a basic picture of processes taking place in large SEP events. We have carried out a detailed study of 17 large SEP events where energetic particle data were fitted by a state-of-the-art model whose computed time-intensity profiles were compared to the observed profiles of H, He, O, and Fe over a very broad energy range. We find that the observed decrease in Fe/O during the rise phase can be reasonably fitted by the transport model where the differences in Fe vs. O transport are due to the slope of the turbulence spectrum of the interplanetary magnetic field (IMF).

Item Type:Book Section
Related URLs:
URLURL TypeDescription
Mason, G. M.0000-0003-2169-9618
Li, G.0000-0001-9313-251X
Cohen, C. M. S.0000-0002-0978-8127
Desai, M. I.0000-0002-7318-6008
Haggerty, D. K.0000-0001-6395-8943
Leske, R. A.0000-0002-0156-2414
Mewaldt, R. A.0000-0003-2178-9111
Zank, G. P.0000-0002-4642-6192
Additional Information:© Copyright 1988 - 2016 - Astronomical Society of the Pacific. This work was supported by NASA under LWS TR&T grant NNX07-AP69G (APL), and other grants including NNX09AP74A (UAH), NNX08AI11G (Caltech), and NNX08AK87G (SwRI) and NSF grants including AGS-1135432(UAH) and ATM-0551127 (SwRI).
Group:Space Radiation Laboratory
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Space Radiation Laboratory2014-01
Series Name:Astronomical Society of the Pacific Conference Series
Record Number:CaltechAUTHORS:20160623-081846895
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:68626
Deposited By: Deborah Miles
Deposited On:29 Jun 2016 19:12
Last Modified:09 Mar 2020 13:19

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