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

We present detailed measurements from the WIND 3D Plasma and Energetic Particle experiment of electron distributions in the deep foreshock, well away from the foreshock boundaries. Both electrons escaping from the magnetosheath and solar wind electrons reflected by the strong magnetic field of the shock are observed. The loss cone angle that separates the reflected electrons from the escaping magnetosheath electrons can be determined as a function of electron energy. At lower energies, the loss cone angle increases because the cross-shock potential tends to pull electrons into the magnetosheath. The loss cone angle is typically £ 30° at energies ³ 100 eV, corresponding to peak shock magnetic field to local magnetic field ratio of ³ 5, while the loss cone variation with energy gives typical shock potentials of ~85 V. Thus the measurements of back-streaming foreshock electrons can be used as a tool to remotely probe the characteristics of the bow shock.

Geophys. Res. Lett., Vol. 23, No. 17, 2203-2206, 1996