Simultaneous measurements of energetic protons and alpha particles by the ISEE 1 and AMPTE/IRM spacecraft in the region upstream of the Earth's bow shock are reported during the period 0700–0900 UT on October 19, 1984. IRM was positioned at about 0900 local time close to the bow shock, whereas ISEE 1 was to the duskside of the bow shock and further upstream. The magnetic field was on average in the Parker spiral direction, so that IRM was connected to the parallel bow shock whereas ISEE 1 was connected for most of the time to the perpendicular bow shock. IRM observes a diffuse distribution over the whole two hour period. In the spacecraft frame an anisotropy exists with more particles streaming toward the bow shock. ISEE 1 observes occasional bursts of energetic ions which exhibit a beam like distribution along the magnetic field away from the bow shock. The occurrence of these beams is in most cases correlated with a change of the longitudinal interplanetary magnetic field direction, such that a field line from the position of the spacecraft meets the shock with a smaller angle between magnetic field and shock normal. The differential intensity at IRM is about one order of magnitude higher than at ISEE 1. Simultaneously measured spectra by AMPTE/CCE within the magnetosphere close to the magnetopause are considerably harder than the spectra at both upstream locations. A comparison of a CCE spectrum in the magnetosheath with an upstream IRM spectrum shows that the proton intensity observed just outside of the magnetopause between 15 and 80 keV is lower than the upstream spectrum. In the magnetosheath the protons stream away from the bow shock toward the magnetopause and the anisotropy increases with energy. Predictions of the magnetospheric leakage model and of the bow shock acceleration model are compared, and it is shown that the observations are consistent with bow shock acceleration, whereas there are extreme difficulties with an explanation in terms of magnetospheric leakage.
