OXYGEN CYCLOTRON HARMONIC-WAVES IN THE DEEP PLASMASPHERE DURING MAGNETIC STORMS

A new approach to the generation of storm-associated ULF waves with di screte spectra (ion cyclotron harmonic waves) observed in the equatori al plasmasphere is presented. It is proposed that the appearance of wa ves with phase velocities smaller than the Alfven velocity is connecte d with a strong dispersion of magnetosonic waves near the bi-ion frequ ency occurring in the presence of oxygen ions of ionospheric origin. T he waves are generated by an instability involving hot oxygen ions wit h loss cone or ring like distributions. Such ions are found in the mag netosphere during magnetic storms. A simple analytical model of this i nstability is elaborated. It is shown that ULF wave observations on bo ard Akebono satellite are in a reasonable agreement with the present t heoretical approach.