The contribution of ion‐cyclotron waves to electron heating and SAR‐arc excitation near the storm‐time plasmapause

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Abstract
The excitation of SAR arcs requires the transfer of energy from the energetic storm‐time ring current ions to tonal electrons located just inside the plasmapause. A recent observational study has indicated that Coulomb scattering with energetic O+ can at times provide sufficient electron hearing to maintain the energy dissipated in SAR arcs, but the question of how this energy is transported to the ionosphere remains unresolved. We demonstrate here that ion‐cyclotron waves can play an important role in both the energy transfer to plasmaspheric electrons and the subsequent downward heat conduction to SAR arc altitudes. Specifically such waves can experience enhanced path integrated amplification along the steep plasmapause density gradient; the later tends to keep the wave normal angle small on several successive bounces across the equator, thus allowing repeated cyclotron‐resonant amplification leading to a total gain of up to 20 e‐foldings. Subsequently, when the wave propagation vector becomes highly oblique, absorption occurs during Landau resonance with thermal plasmaspheric electrons. This increases the electron temperature in the direction parallel to the ambient field and leads directly to heat conduction into the ionosphere.