Pitch-angle distributions and anisotropies of energetic particles at the termination shock: theory vs. Voyager observations

Details Pitch-angle distributions and anisotropies of energetic particles at the termination shock: theory vs. Voyager observations Pitch-angle distributions and anisotropies of energetic particles at the termination shock: theory vs. Voyager observations

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsh53a..07f&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #SH53A-07

Physics

2124 Heliopause And Solar Wind Termination, 2152 Pickup Ions, 7845 Particle Acceleration, 7851 Shock Waves (4455), 7859 Transport Processes

Scientific paper

We analyze and model plasma-frame pitch-angle distributions of low-energy accelerated ions observed by Voyager 1 in the immediate vicinity of the termination shock (TS). In view of limited applicability of Parker's transport equation to highly beamed upstream populations we developed a novel technique employing a three- moment expansion of the focused transport equation in Legendre harmonics. For the first time high temporal resolution LECP measurements are combined with Voyager magnetometer data to elucidate the dependence of the three Legendre harmonics (intensity, first-order anisotropy, and second-order anisotropy) on particle energy. Our analysis of pitch-angle and spatial distributions indicate that the observed low-energy populations were accelerated by a highly oblique shock wave (i.e., the TS). We show that measured intensities peak sharply at the shock crossing consistent with theoretical predictions of adiabatic reflection off a highly oblique shock. We show how derived first- and second-order anisotropies can be used to deduce the local obliquity of the TS at the time of crossing. The model predicts upstream anisotropies as high as 100% for a nearly perpendicular TS, whereas downstream distributions are nearly isotropic in all cases.

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