INTERBALL-Auroral observations of 0.1-12 keV ion gaps in the diffuse auroral zone

We examine ion Aux dropouts detected by INTERBALL-Auroral upon traversal of the auroral zone at altitudes of similar to 13 000 up to 20 000 km. These dropouts which we refer to as "gaps", are frequently observed irrespectivel y of longitudinal sector and appear characteristic of INTERBALL-Auroral ion spectrograms. Whereas some of these gaps display a nearly monoenergetic ch aracter (similar to 12keV), others occur at energies of a few hundreds of e V up to several keV. INTERBALL-Auroral data exhibit the former monoenergeti c gap variety essentially in the evening sector. As examined ill previous s tudies, these gaps appear related to transition from particle orbits that a re connected with the magnetotail plasma source to closed orbits encircling the Earth. The latter gap variety, which spreads over several hundreds of eV to a few keV is often observed in the dayside magnetosphere. It is argue d that such gaps are due to magaetospheric residence times well above the i on lifetime. This interpretation is supported by numerical orbit calculatio ns which reveal extremely large (up to several tens of hours) times of flig ht in a limited energy range as a result of conflicting E x B and gradient- curvature drifts. The characteristic energies obtained numerically depend u pon both longitude and latitude and are quite consistent with those measure d insitu.