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Constraints on Mechanisms for Longitudinal Spreading of Impulsive SEPs from Multispacecraft Observations of Scatter-free Events

Wiedenbeck, M. E. and Cohen, C. M. S. and Klassen, A. and Leske, R. A. and Liewer, P. A. and Mason, G. M. and Nitta, N. V. (2015) Constraints on Mechanisms for Longitudinal Spreading of Impulsive SEPs from Multispacecraft Observations of Scatter-free Events. In: 34th International Cosmic Ray Conference (ICRC2015). Proceedings of Science. No.236. SISSA , Trieste, Italy, Art. No. 106.

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Impulsive solar energetic particle (ISEP) events are understood to involve particle acceleration in relatively compact regions of the solar corona where reconnection causes the release of magnetic energy and produces both turbulence and larger scale motions that can interact with and accelerate charged particles. In many cases the longitudinal spread of ISEPs observed at 1 AU is relatively narrow and possibly consistent with a point source of acceleration. However, several ISEP events observed with the two STEREO spacecraft and near-Earth instruments have had exceptionally wide longitudinal spreads, sometimes significantly greater than 90°. It has been suggested that this spreading could be caused by interplanetary scattering in conjunction with corotation of the interplanetary field. There exists a subset of ISEP events that are referred to as “scatter free” due to characteristics such as velocity dispersion, strong particle anisotropy, and/or flux dropouts observed at 1 AU. We report on scatter-free events observed by both of the STEREOs in 2014 when the spacecraft were separated by 38°. Producing such a large spread in the absence of significant interplanetary scattering requires a process other than cross-field diffusion for the longitudinal transport and suggests that the spreading could have its origin in the solar corona.

Item Type:Book Section
Related URLs:
URLURL TypeDescription Section
Wiedenbeck, M. E.0000-0002-2825-3128
Cohen, C. M. S.0000-0002-0978-8127
Leske, R. A.0000-0002-0156-2414
Mason, G. M.0000-0003-2169-9618
Additional Information:Copyright owned by the author(s) under the term of the Creative Commons Attribution-NonCommercial-ShareAlike. We thank Joe Giacalone for his comments on field line random walk. This work was supported by NASA at JPL, Caltech, APL, and LMSAL. The STEREO/SEPT projects are supported under Grant 50 OC 1302 by the German Bundesministerium für Wirtschaft through the Deutsches Zentrum für Luft- und Raumfahrt (DLR).
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Deutsches Zentrum für Luft- und Raumfahrt (DLR)50 OC 1302
Bundesministerium für Wirtschaft und Technologie (BMWi)UNSPECIFIED
Series Name:Proceedings of Science
Issue or Number:236
Record Number:CaltechAUTHORS:20180828-122926312
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89246
Deposited By: George Porter
Deposited On:30 Aug 2018 20:42
Last Modified:16 Nov 2021 00:33

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