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| Paper: |
Observations of Loss-Cone Pitch Angle Distributions of Solar Energetic Particles |
| Volume: |
484, Outstanding Problems in Heliophysics: From Coronal Heating to the Edge of the Heliosphere |
| Page: |
117 |
| Authors: |
Leske, R. A.; Cummings, A. C.; Cohen, C. M. S.; Mewaldt, R. A.; Labrador, A. W.; Stone, E. C.; Wiedenbeck, M. E.; Christian, E. R.; von Rosenvinge, T. T. |
| Abstract: |
Pitch angle distributions of solar energetic
particles (SEPs) in interplanetary space sometimes exhibit a loss cone
in which an incident beam of particles is partially mirrored;
particles with large pitch angles are reflected while those with smaller
pitch angles are not. Mirroring requires a magnetic field enhancement,
but if the field strength is not large enough to turn
around particles with the smallest pitch angles or if these
particles scatter before reaching their more distant mirror points,
a loss cone forms. Such distributions therefore
provide information on the interplanetary environment far from the spacecraft.
The Low Energy Telescopes onboard the twin STEREO spacecraft
have detected loss-cone distributions in several SEP events. We
present some of these and other interesting anisotropy observations,
and discuss their implications for SEP transport.
In particular, we find that the shapes of the
pitch angle distributions generally vary with energy and species, with lower
energy particles usually more anisotropic than higher energy particles.
Comparison with theory may be used to determine the energy and rigidity
dependences of the pitch angle diffusion coefficient. |
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