Energy transport during O+ energization by ELF waves observed by the Frejasatellite

We present a study of strong ELF waves correlated with Of ion heating. We i nvestigate the kinetic energy flux of oxygen ions and electrons parallel to the ambient magnetic field and the Poynting flux along the magnetic field of waves in different frequency regions. We show that the Poynting flux of lower hybrid waves and waves with frequencies below the oxygen gyrofrequenc y is downward but much less than the upgoing oxygen ion energy flux. The Po ynting flux of ELF waves with frequencies at about half the local proton gy rofrequency is also downward, and it is comparable to, or larger, than the upward oxygen energy flux. Our results are consistent with a scenario where ELF waves with frequencies around half the proton gyrofrequency are genera ted above the satellite and transfer energy to oxygen ions in a region belo w the satellite.