12-20 July 2017
Asia/Seoul timezone
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BEXCO - Room C(109/110)

[SH022] Magnetic Fluctuations and Peculiar Anisotropy Oscillations in the 23 July 2012 SEP Event


  • Richard LESKE

Primary authors



The pitch-angle distributions of solar energetic particles (SEPs) provide a wealth of information about particle transport through interplanetary space, and can 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. We have previously reported apparent "oscillations" in the pitch-angle width of this beam when using measurements at a 1-minute cadence. After further analysis we find this behavior is largely a result of relatively rapid variations in the magnetic field direction along with the fact that energetic particles average over much larger spatial and temporal scales than represented by solar wind measurements at the same cadence. Analysis of similar differences between directions of peak particle intensities and magnetic field directions in earlier events by others have been interpreted in terms of magnetic turbulence. We review the STEREO/LET anisotropy observations made during the 23 July 2012 event, present our new interpretation of the apparent oscillations as arising from the effects of magnetic turbulence on the calculated particle pitch angle distributions, and discuss the implications of these observations for SEP transport in the heliosphere.