Electric field Deformation and Behavior of the Suprathermal Ionospheric Ions Observed in Density Depletion Regions in the High Altitude Auroral Ionosphere

The nominal wave forms measured by the electric field detector (EFD) onboard Akebono(Exos-D) satellite are sine curves of the satellite spin period. However, for some short periods near its apogee when the satellite passes over the auroral latitudes, the observed wave forms are either deformed significantly from sinosuidal or characterized by very small amplitude. The deformation of the wave form or extreme decrease in amplitude is correlated with energetic electron precipitation measured by the low energy plasma (LEP) instrument onboard. Hence, it has been considered that these wave form deformations are caused by the density depletion in the auroral acceleration region. The transition from normal sine wave to deformed wave form occurs within a spin period of 8 second, less than 50 km along the trajectory of the spacecraft at the apogee altitude of 9000km. We will discuss the cause of these abnormal wave form structures using data from the suprathermal ion mass spectrometer(SMS) onboard which has not been included in the analysis previously.