TRANSVERSE ION ENERGIZATION AND WAVE EMISSIONS OBSERVED BY THE FREJA SATELLITE

Observations by the Freja satellite at altitudes of about 1700 km in the auroral zone sometimes show energization of both light and heavy ions to characteristic energies of up to about 50-100 eV. This ion heating is often associated with lower hybrid waves, and also with wave emissions at lower frequencies. No obvious decrease of electric field wave power below the proton gyrofrequency, reported by other spacecraft at similar altitudes, is observed in the regions of intense ion heating. Furthermore, localized density depletions associated with lower hybrid waves have not been detected in these regions. We present a preliminary model where waves observed during an event in the evening-side auroral zone are used to explain the observed ion energies.