PROBING THE EARTH BOW SHOCK WITH UPSTREAM ELECTRONS

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 mag netic field of the shock are observed. The loss cone angle that separa tes 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 typi cally less than or equal to 30 degrees at energies greater than or equ al to 100 eV, corresponding to peak shock magnetic field to local magn etic field ratio of greater than or equal to 5, while the loss cone va riation with energy gives typical shock potentials of similar to 85 V. Thus the measurements of back-streaming foreshock electrons can be us ed as a tool to remotely probe the characteristics of the bow shock.