Unified theory of SAR arc formation at the plasmapause

We propose that SAR arcs are generated at the plasmapause as a consequence of the turbulent dissipation of ring current energy. During the recovery phase of a geomagnetic storm, the plasmapause expands outward into the symmetric ring current. When the cold plasma densities reach about 100 cm−3, ring current protons (Ep∼20 kev) become unstable and generate intense ion cyclotron wave turbulence in a narrow region ½ RE wide (just inside the plasmapause). Approximately one-half of the ring current energy is dissipated into wave turbulence, which in turn is absorbed through a Landau resonant interaction with plasmaspheric electrons. The combined thermal heat flux to the ionosphere due to Landau absorption of the wave energy and proton-electron Coulomb dissipation is sufficient to drive SAR arcs at the observed intensities. We thus predict that the arcs should be localized to a narrow latitudinal range just within the stormtime plasmapause. They should occur at all local times and persist for the 10- to 20-hour duration of the plasmapause expansion. Expected proton precipitation fluxes will not contaminate the spectral purity of SAR arcs.