Coupled Ion Acceleration and Wave Excitation at Earth's Bow Shock

A brief observational and theoretical history of coupled ion acceleration and wave excitation at Earth's bow shock is presented including the "reflected" (R), "intermediate" (I), and "diffuse" (D) ion populations, the ultra-low-frequency (ULF) waves upstream of Earth's bow shock, and the spatial structure of the wave and ion "foreshock". Emphasis is placed on the spatial transition of the bow shock from "quasi-perpendicular" to "quasi-parallel". In addition, the origin of the ions, the acceleration of electrons, the downstream "thermalization" of ions at weak quasi-perpendicular portions of the shock, and the foreshocks observed at other planets are reviewed. The current understanding of these phenomena is assessed. Finally, a few issues which remain unresolved or controversial since the era of the ISEE 1, 2, and 3 spacecraft are discussed including the origin of the exponential ion energy spectra, the ion "injection" mechanisms at the shock, and the relative contribution of magnetospheric ions to the diffuse ion population.