Acceleration of Energetic Ions at the Earth's Perpendicular Shock: 3D Observations
K. Meziane, A. J. Hull, R. P. Lin, T. J. Freeman, D. E. Larson
	Space Sciences Laboratory, University of California, Berkeley, CA, USA
G. K. Parks,
	University of Washington, Seattle, WA, USA

We discuss in detail the observation of energetic ions (30 keV - 1 MeV) measured by the WIND-3DP Plasma and Energetic Particle experiment at the Earth's bow shock. The events are observed near the electron foreshock boundary, and it seems that their occurence requires the presence of a relatively high ion flux of ambient energetic ions as in CIR or SEP events.
Upstream, the ion energy-spectrum is usually peaked at few hundreds of keV. The ion propagate upstream with an angular distribution peaked at 30 degrees pitch-angle. However, the angular distribution is non-gyrotropic with a range of gyrophase <~ 180 degrees. In the downstream side of the shock, the angular distribution of energetic particles is peaked at ~ 90 degrees and also appears non gyrotropic.
We study the gyrophase range versus the energy and the shock velocity along the upstream field line; we compare the results with particle simulations.
On the other hand, we show that the energy-spectrum is consistent with an adiabatic-like reflection at the shock of the incoming CIR ions. However, the pitch angle distribution is satisfied only within a certain range of gyrophase angle. Similar comparison is made for energetic ions observed downstream.