TRANSVERSE ION ENERGIZATION AND WAVE EMISSIONS OBSERVED BY THE FREJA SATELLITE

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