Cyclotron absorption of ion-cyclotron waves at the bi-ion frequency

We demonstrate that geomagnetically trapped ion-cyclotron waves that are generated near the equator with frequencies below ΩHe+, can experience significant O+ cyclotron resonant absorption near the reflection point at frequencies just above the bi-ion frequency. The absorption is strongest when the wave normal angle is highly oblique and when the heavy ions are relatively hot (T > 1 keV) with a concentration of no more than 1 or 2%. This suggests that wave absorption near the bi-ion frequency could contribute to the heating process for energetic ring current O+; in the outer radiation zone during geomagnetic storms.