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Magnetic Fluctuations and Peculiar Anisotropy Oscillations in the 23 July 2012 SEP Event

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. (2017) Magnetic Fluctuations and Peculiar Anisotropy Oscillations in the 23 July 2012 SEP Event. In: 35th International Cosmic Ray Conference (ICRC2017). Proceedings of Science. No.301. SISSA , Trieste, Italy, Art. No. 144.

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The pitch-angle distributions of solar energetic particles (SEPs) provide a wealth of information about particle transport through interplanetary space, and depend on the magnetic field strength, topology, and turbulence at remote heliospheric locations. The Low Energy Telescope (LET) on STEREO measures angular distributions in the ecliptic for SEP ions from protons to iron with energies of about 2--12 MeV/nucleon. At the onset of the 23 July 2012 extreme SEP event, a beamed distribution was observed at STEREO-Ahead using LET. We have previously reported apparent "oscillations" in the pitch-angle width of this beam when using simultaneous particle and magnetic field measurements at a 1-minute cadence. We have now determined that this behavior is largely a result of the effects of magnetic turbulence on the calculated particle pitch angle distributions. The locally measured magnetic field direction varies relatively rapidly, while the energetic particle distribution is governed by magnetic fields averaged over much larger spatial and temporal scales than represented by solar wind measurements at the same cadence. Similar behavior in earlier events has been reported by others and analyzed in the framework of quasilinear theory.

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-NoDerivatives 4.0 International License. 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 00008864 from the University of California at Berkeley under NASA grant NNX15AG09G. We thank the STEREO/MAG team for making their data publicly available, and we thank Andrew Davis and Chris Russell for help in understanding the LET and MAG data timetags.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Series Name:Proceedings of Science
Issue or Number:301
Record Number:CaltechAUTHORS:20180828-122926202
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89245
Deposited By: George Porter
Deposited On:30 Aug 2018 20:33
Last Modified:09 Mar 2020 13:19

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