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Insights Into Particle Transport Obtained from Solar Energetic Particle Anisotropies

Leske, R. A. and Cummings, A. C. and Cohen, C. M. S. and Mewaldt, R. A. and Labrador, A. W. and Stone, E. C. and Wiedenbeck, M. E. and Christian, E. R. and von Rosenvinge, T. T. (2015) Insights Into Particle Transport Obtained from Solar Energetic Particle Anisotropies. In: 34th International Cosmic Ray Conference (ICRC2015) - Solar and Heliospheric Physics: Experimental Results. Proceedings of Science. No.236. SISSA , Trieste, Italy, Art. No. 072.

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Solar energetic particle (SEP) pitch-angle distributions are shaped by the competing effects of magnetic focusing and scattering as the particles travel through interplanetary space. Therefore, measurements of SEP anisotropies provide insight into particle transport and can probe interplanetary conditions at remote locations from the observer. The Low Energy Telescopes (LETs) onboard the twin STEREO spacecraft measure pitch-angle distributions for protons and heavier ions at energies of about 2-12 MeV/nucleon. Using these instruments, we have observed a wide variety of SEP anisotropies, such as bidirectional flows within interplanetary coronal mass ejections, sunward-flowing particles when the spacecraft was magnetically connected to the back side of a distant shock, and loss-cone distributions in which particles with large pitch angles magnetically mirror at an interplanetary field enhancement that is too weak to reflect particles with the smallest pitch angles. One of the more puzzling observations is unusual oscillations on a timescale of several minutes in the width of a beamed distribution at the onset of the very large 23 July 2012 SEP event. We report LET anisotropy observations at both STEREO spacecraft during the extreme event of 23 July 2012, in which a large range of anisotropies were observed at various times during the event, and discuss their implications for SEP transport.

Item Type:Book Section
Related URLs:
URLURL TypeDescription
Leske, R. A.0000-0002-0156-2414
Cummings, A. C.0000-0002-3840-7696
Cohen, C. M. S.0000-0002-0978-8127
Mewaldt, R. A.0000-0003-2178-9111
Labrador, A. W.0000-0001-9178-5349
Stone, E. C.0000-0002-2010-5462
Wiedenbeck, M. E.0000-0002-2825-3128
Christian, E. R.0000-0003-2134-3937
Additional Information:Copyright owned by the author(s) under the term of the Creative Commons Attribution-NonCommercial-ShareAlike. This work was supported by the National Aeronautics and Space Administration (NASA) at the California Institute of Technology and the Jet Propulsion Laboratory under sub-contract SA2715-26309 from the University of California at Berkeley under NASA contract NAS5-03131, and by NASA award NNX08AK87G. We thank the STEREO/PLASTIC (NASA contract NAS5-00132), MAG, and SWEA teams for making their data publicly available, and Lan Jian and Ying Liu for helpful discussions.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Series Name:Proceedings of Science
Issue or Number:236
Record Number:CaltechAUTHORS:20180910-131322207
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89502
Deposited By: George Porter
Deposited On:10 Sep 2018 20:46
Last Modified:16 Nov 2021 00:35

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