Energization of solar wind ions by reflection from the earth's bow shock

The existence of ion beams with energies a few times the solar wind energy and streaming outward from the earth's bow shock has been known for some time. To explain the observed ion energies, a simple reflection model has been proposed in which the particles gain energy by displacement parallel to the interplanetary electric field. In this model the energy gained in the reflection can be described as a function of the angles between the interplanetary magnetic field, the solar wind velocity, and the local shock normal. Ion beams under widely varying conditions have been observed with Los Alamos Scientific Laboratory/Max-Planck-Institut instrumentation on Isee 1 and 2. For 18 cases, with beam energies ranging from approx.1.4 to approx.30 times the solar wind energy, a comparison between the observed and the predicted beam energies has been made. Good agreement between the reflection theory and the observations has been found. Thus simple reflection can account for the several keV ion beams observed upstream from the earth's bow shock