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Published 2013 | Published
Book Section - Chapter Open

A survey of anisotropic energetic particle flows observed by STEREO


The Low Energy Telescopes (LETs) onboard the twin STEREO spacecraft have been measuring the anisotropies of energetic particles since before the beginning of solar cycle 24. Large unidirectional anisotropies often appear at the onset of magnetically well-connected solar energetic particle (SEP) events, suggesting beamed particles with relatively little scattering. Also, long-lasting bidirectional flows are seen during the decay phase of several SEP events. Some of these instances appear to be within interplanetary coronal mass ejections (ICMEs), as indicated by characteristics such as magnetic field rotations or bidirectional suprathermal electrons. We present preliminary findings from a survey of LET proton anisotropy observations, which illustrate that bidirectional flows appear more likely to come from directions far from the nominal Parker spiral direction than do unidirectional beams, consistent with previous studies. Individual cases that show unusual intensity depletions perpendicular to the magnetic field or pitch angle distributions otherwise indicative of magnetic mirroring are presented in more detail.

Additional Information

© 2013 AIP Publishing LLC. This work was supported by the National Aeronautics and Space Administration (NASA) at Caltech and JPL 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 MAG investigators on STEREO formaking their data publicly available.

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August 19, 2023
January 13, 2024