LOCAL TIME OCCURRENCE FREQUENCY OF ENERGETIC IONS IN THE EARTHS MAGNETOSHEATH

The occurrence frequency of energetic ions in the energy range from 8 to 40 keV/e as a function of local time in the magnetosheath is presented. Energetic ions are observed in the magnetosheath with a minimum probability of 25% for all local times. The occurrence frequency for the energetic ions is higher on the dawnside than on the duskside but shows a relative maximum post-noon in the local time range from 12 to 15 hours. The post-noon relative maximum is attributed to a magnetospheric source for the energetic ions while the dawn-dusk asymmetry is attributed to a quasi-parallel bow shock source.