Acceleration of energetic ions at the earth's near perpendicular shock: Three-dimensional observations

We discuss in detail the observation of energetic ions (30 keV-2 MeV) measured by the WIND-3D Plasma and Energetic Particle experiment at the Earth's bow shock. The events are observed near the perpendicular shock, and it seems that their occurrence requires the presence of a relatively high ion flux of ambient energetic ions as in Corotating Interaction Region or Solar Energetic Particle events. Upstream, the ion energy spectrum is usually peaked at a few hundred keV. The ions propagate upstream with an angular distribution peaked at 150 deg. pitch-angle. However, the angular distribution is non-gyrotropic with a range of gyrophase ≤180 deg. . In the downstream side of the shock, the angular distribution of energetic particles is peaked at ∼90 deg. and is also non-gyrotropic. We show that the energy-spectrum is consistent with an adiabatic-like reflection at the shock of the incoming Corotating Interaction Region ions. However, the pitch angle distribution is satisfied only within a certain range of gyrophase angle. A similar comparison is made for energetic ions observed downstream