Statistical properties of the multiple ion band structures observed by the FAST satellite

Abstract

Data of low-energy (<28 keV) H+ and O+ ions obtained by the FAST satellite were used to investigate the statistical properties of multiple ion band structures (MIBS) that are characterized by multiple O+/H+ components with discrete energies. MIBS distributions for H+ and O+ ions had different relationships with the AL index, invariant latitude (ILAT), and magnetic local time, suggesting different formation mechanisms. O+ MIBSs were observed during magnetically active periods around the equatorward boundary of the auroral oval mainly in the dusk and midnight sectors, while H+ MIBSs were observed during quiet times at higher latitudes in the dawn and dusk sectors. O+ MIBSs shifted toward lower latitudes with decreasing AL index due to the expansion of the auroral oval during magnetically active periods. Both maximum and minimum energies of O+ MIBSs decrease with decreasing ILAT, which is consistent with velocity filter effects caused by convective transport from high to low latitudes in the nightside. The statistical properties obtained from the FAST observations suggest that O + MIBSs supply O+ ions from the ionosphere to the inner magnetosphere during magnetic storms and contribute to the storm time ring current development. Copyright 2008 by the American Geophysical Union.