Proton observations supporting the ion cyclotron wave heating theory of SAR arc formation

Low altitude satellite observations of precipitated and locally mirroring protons during periods of ground-based SAR arc observations are presented. The SAR arcs are found to be located in a region with significantly enhanced proton pitch angle scattering and enhanced electron temperature, but inside the plasmapause where the proton pitch angle distribution is anisotropic. The increase in the pitch angle scattering takes place in a localised region having a width of a few tenths of an L-value. The observations can favourably be accounted for by the Cornwall et al. (1971) theory for the SAR arc formation. Using observed proton fluxes and typical energy spectra, the expected Hβ intensity in the SAR arc region is estimated to be a few Rayleighs, and the energy flux from precipitated protons above a few keV to be 10-2 - 10-1 ergs/cm2sec. These estimates are in reasonable agreement with previously published theoretical and experimental values. Simultaneous ground-based observations of Hα emissions were found in the region of intense, isotropic proton precipitation located outside the plasmapause. (Auth.)