Energetic ions upstream of the Earth's bow shock: INTERBALL-1 survey

A statistical survey of energetic ions (> 20 keV) observed by the DOK2 experiment on Interball-1 during foreshock intervals from 1996 to 1998 is presented. Flux levels depend on the connection geometry, with higher values at quasi-parallel shocks, particularly at lower energies. The decrease of flux in diffusive events with distance from the bow shock is consistent with results from earlier surveys performed closer to the bow shock. The energy spectra are softer for quasi-parallel than quasi-perpendicular connections. The reflected ions have musch softer spectra. The cumulative frequencies for flux level occurrence patterns exhibit differences for quasi-parallel and quasi-perpendicular geometries up to approximately 200 keV.