Abstract
During two diffuse energetic ion events upstream of the Earth's bow shock with radial interplanetary magnetic field conditions comprehensive energy spectra of the protons and power spectra of the magnetic field fluctuations were obtained with the instrumentation on AMPTE/IRM. For diffuse ions a continuous distribution from ≈ 5 keV (starting above the solar wind energy) to the instrumental limit (230 keV/e) is found upstream and downstream of the shock. This strongly indicates a single source for the upstream diffuse ion population over the total energy range. Assuming that the ions are shock accelerated, an efficiency for the production of upstream energetic ions of ≈ 4 to 11% is found by comparing the energy flux densities of the energetic ions and of the incoming solar wind. The lower value is observed during the period with a low interplanetary magnetic field strength. The measured energy densities of the particles and the waves are compared with the self‐consistent model of Fermi acceleration by Lee (1982) which includes the coupled wave and particle behaviour. The theoretically predicted wave energy density is in excellent agreement with the observed wave energy density.
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