Unified theory of SAR arc formation at the plasmapause

TLDR

During the recovery phase of a geomagnetic storm, the plasmapause expands outward into the symmetric ring current. The study proposes that SAR arcs are generated at the plasmapause as a consequence of turbulent dissipation of ring‑current energy. When cold plasma densities reach ~100 cm⁻³, ring‑current protons become unstable and generate intense ion‑cyclotron wave turbulence in a narrow region just inside the plasmapause, and about half of the ring‑current energy is dissipated into this turbulence, which is then absorbed via Landau resonance with plasmaspheric electrons. The combined heat flux from Landau absorption and proton‑electron Coulomb dissipation is sufficient to drive SAR arcs at observed intensities, predicts that the arcs are localized just inside the stormtime plasmapause, occur at all local times for 10–20 h, and are not contaminated by proton precipitation.

Abstract

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.