Modeling pitch-angle and gyrophase restricted ~0.5~MeV foreshock ions

Details Modeling pitch-angle and gyrophase restricted ~0.5~MeV foreshock ions Modeling pitch-angle and gyrophase restricted ~0.5~MeV foreshock ions

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsm33b..02w&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #SM33B-02

Physics

2114 Energetic Particles (7514), 2154 Planetary Bow Shocks, 2451 Particle Acceleration, 7807 Charged Particle Motion And Acceleration

Scientific paper

Ions with energies > 100~keV backstreaming from the bow shock have been well-studied, with most observed fitting into three catagories: those with isotropic distributions accelerated via diffusive processes, typically having energies no greater than 250 keV; those with pitch angle, and sometimes gyrophase, constrained distributions extending past 1 MeV in energy, accelerated during single encounters with the shock via the shock drift mechanism; and those of magnetospheric origin that `leak' across the magnetopasue and find their way to the upstream. In principle, some of these mechanisms could act in concert, although that has not been examined thoroughly. We have examined relatively infrequent Wind/3DP observations that appear to be of the second type (restricted in pitch angle and gyrophase), but which have no apparent source of seed particles needed to produce the observed fluxes using straightforward application of shock drift acceleration theory. Due to the different travel times required for ions of different pitch angles and energies to travel from the shock to the spacecraft, and gyrophase dependent trajectories for ions with gyroradii of the order of an Earth radius, a single distribution snapshot is a convolution of sources that can be well-distributed along the bow shock. In order to better understand our observations we have applied particle tracking methods to find how ions at different energies and arrival directions map back to the shock, which permits us to model point-by-point contributions to the distributions observed at the spacecraft. We present results from this investigation, and consider different hypotheses for producing the unobserved, but required, seed populations.

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