Ion cyclotron absorption at the second harmonic of the oxygen gyrofrequency

The ray paths of unstable electromagnetic waves generated inside the plasmapause during magnetic storm conditions are followed using the HOTRAY code. Unducted waves which are preferentially generated in the field aligned direction are rapidly refracted to large wave normal angles. At frequencies between the Oxygen and Helium gyrofrequencies the waves reflect once their frequency falls below the bi‐ion frequency and the waves subsequently bounce back and forth across the equator. The wave energy is ultimately absorbed by Landau resonance with plasmaspheric electrons or by second harmonic cyclotron resonance with thermal Oxygen; the latter being an important effect which has not previously been considered. Both processes may provide a significant heating mechanism for either population during storms.

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