Auroral ionospheric ion feeding of the inner plasma sheet during substorms

During the last decade, satellite observations in the nightside magnetosphere have confirmed the presence of energetic (>20 keV) ionospheric-origin ions in the near-Earth magnetotail. Observations also imply that the feeding of the equatorial magnetosphere with ions from the high-latitude ionosphere can be very fast and intense at times. In the present paper we use observations from the Combined Release and Radiation Effects Satellite (CRRES) to investigate the characteristics of ion energy density variations. Multispecies studies of the energy density give important clues on the coupling of the different plasma sources and their participation in the substorm energization. The measurements, coming from the Magnetospheric Ion Composition Spectrometer (MICS), confirm previous results obtained from the AMPTE/CCE-CHEM spectrometer, with regard to the timing of the high-latitude ionosphere response to the equatorial magnetosphere disturbances. The energy density profile of the ionospheric-origin O⁺ follows the intensity enhancements of the westward electrojet very closely in time, exhibiting a continuing increase, contrary to the behaviour of the other major ion species H⁺ and He⁺⁺. This feature, which is consistent with statistical studies of AMPTE/CCE observations, points towards a fast activation of an extraction/acceleration mechanism which feeds the inner plasma sheet with ions of ionospheric origin during the substorm expansion.