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

K. Meziane, R. P. Lin, G. K. Parks, D. E. Larson, S. D. Bale, G. M. Mason, J. R. Dwyer, and R. P. Lepping

Space Sciences Laboratory, University of California, Berkeley, CA 94720

Abstract:

On December 6, 1994, during a CIR (Corotating Interaction Region) event, the WIND 3D-Plasma and energetic particle experiment observed a burst (£ 24 s) of 238-676 keV protons close to the electron foreshock boundary, followed by a 156-236 keV, 101-156 keV and 33-101 keV proton bursts about ~40 s, 65 s and 85 s later, respectively. Similar dispersed bursts of helium with energies between ~50 keV and 1 MeV followed the proton bursts. During this time, the IMF direction varied slowly with an almost monotonic decrease in qBn. The proton energy spectrum is initially peaked at ~350 keV, and progresses to lower energies with time. The proton 3D angular distributions are peaked at ~30 pitch-angle, propagating away from the shock, but they are non-gyrotropic. Finally, we show that the proton energy-spectra as well as the pitch angle distribution agree quantitatively with a model of a single adiabatic reflection of the incident energetic interplanetary ions by the quasi-perpendicular shock.

Geophys. Res. Lett., Vol. 26, No. 19, 1999