H+ AND HE2+ HEATING AT THE EARTHS BOW SHOCK

The origins of ion heating at the Earth's bow shock are explored for a wide range of Mach numbers using data from composition experiments that separate solar wind H+ and He-2+ downstream from the shock. Both of these ion species are important in the production of low-frequency waves in the downstream magnetosheath. Consistent with previous results, the majority of the H+ dissipation at the bow shock is provided by a relatively small amount of the incident solar wind distribution that specularly reflects off the shock and returns to the downstream region. Although the He-2+ distribution downstream from the shock may show some evidence for a reflected-returned component, this component has a much lower relative density compared to that of the analogous H+ component and does not have the same strong Mach number dependence. Thus in contrast to the H+ results, the He-2+ dissipation at the shock is provided by the directly transmitted core of the distribution.