Beams of protons and alpha particles ≳30 keV/charge from the Earth's bow shock

We have investigated two beamlike particle events (30 keV/charge to 160 keV/charge) upstream of the earth's bow shock with the Max‐Planck‐Institut/University of Maryland ultralow energy and charge analyzer on Isee 1. These beams consist of protons as well as of alpha particles, and the spectra are generally steep and are decreasing with increasing energy. During one event the spectra of both protons and alpha particles have a maximum at ∼65 keV/charge. During these events the interplanetary magnetic field through the satellite position was almost tangent to the bow shock, and application of the theory of acceleration predicts acceleration of a solar wind particle up to 60 keV/nucleon in a single reflection. The observation of reflected protons as well as alpha particles has implications for the physical reflection process usually not discussed in the acceleration theories.