Evidence for acceleration of ions to similar to 1 MeV by adiabatic-like reflection at the quasi-perpendicular Earth's bow shock

On December 6, 1994, during a CIR (Corotating Interaction Region) event, th e WIND 3D-Plasma and energetic particle experiment observed a burst (less t han or equal to 24 s) of 238-676 keV protons close to the electron foreshoc k boundary, followed by a 156-236 keV, 101-156 keV and 33-101 keV proton bu rsts about similar to 40 s, 65 s and 85 s later, respectively. Similar disp ersed bursts of helium with energies between similar to 50 keV and similar to 1 MeV followed the proton bursts. During this time, the IMF direction va ried slowly with an almost monotonic decrease in theta(Bn). The proton ener gy spectrum is initially peaked at similar to 350 keV, and progresses to lo wer energies with time. The proton 3D angular distributions are peaked at s imilar to 30 degrees pitch-angle, propagating away from the shock, but they are non-gyrotropic. Finally, we show that the proton energy-spectra as wel l as the pitch angle distribution agree quantitatively with a model of a si ngle adiabatic reflection of the incident energetic interplanetary ions by the quasi-perpendicular shock.