We report measurements of H+ and He++ ions in field‐aligned beams (∼ 10 keV/nuc) made with the AMPTECCE spacecraft. The proton beam population has a density ≲ 1% of the solar wind density and a significant thermal anisotropy (ω⟂ > ω∥), in agreement with previous observations. The beam density is found to be anti‐correlated with the angle θBn. The observed beam velocities are in reasonable agreement with the “direct reflection” model, in which a portion of the solar wind is reflected and energized at the earth's bow shock, but are consistently larger than expected from magnetosheath leakage models. The He++ ions in the beams have approximately the same velocity as the H+ ions, but the He++ to H+ density ratio is dramatically smaller than that measured simultaneously in the solar wind. Our beam observations were obtained during several of the time intervals previously analyzed by other workers, using data from the same spacecraft, who attributed the streaming upstream ions to magnetospheric rather than bow shock origin.
