Measurements of bow shock particles far upstream from the earth

Electrons and ions moving upstream frequently appear at distances up to 240 R/sub E/ from earth at times when the direction of the interplanetary magnetic field allows their propagation from the bow shock. Strong asymmetries in the ion angular pitch angle distribution are often observed, a consequence of the sharp gradient in guiding center density and very weak scattering. The gradient is due to the restricted spatial region over which these particles are accelerated. The solar wind electric field, E = -V/sub sw/ x B/sub imf/ acts on these particles and produces striking effects in both the ion angular distributions and the ion energy spectra. The frequent occurrence of these effects implies that the source region of the diffuse ions at the bow shock is not more than a few times 104 km