AUREOL-3 Results on Ion Precipitation

This paper attempts to summarize recent experimental studies on suprathermal (<14 keV) ion precipitation in the morning side auroral zone from ion composition data provided by the low-altitude (400-2000 km) AUREOL-3 polar orbiting satellite. Plasma measurements show that on auroral and polar cap field-lines upflowing ionospheric ions, mostly O + and H + , are commonly observed. Imbedded in the discrete auroral region different narrow bands of ion precipitation are observed with a clear energy-lattitude dispersion. These structures can be interpreted as H + ion beams which have experienced velocity filter effects after ejection either from the conjugate ionosphere or from reconnection regions in the magnetotail. Finally the low energy (< 200 eV) ion precipitation (H + , O + , He + ) found equatoward of the precipitation region of more energetic and adiabatically accelerated ions can be satisfactorily explained by the drift of ionospheric ions, ejected with conical distributions and then convected earthward and eastward in a few bounce times.