Characteristics and sources of E-region ionization in the continuous aurora

The continuous aurora is defined as E-region ionization that is steady in time and uniformly distributed over a large portion of the auroral oval. We have studied the characteristics and sources of ionization in the continuous aurora using data from the Chatanika radar and the DMSP AND NOAA satellites. The predominant source of ionization in the continuous aurora is precipitating electrons. The energy distribution of these energetic electrons is approximately Maxwellian. Satellite measurements of electron fluxes can be used to infer the ionospheric electron density along the path of the satelllite in the altitude range 90 to 160 km. However, these calculations underestimate the actual electron density when other ionization sources are present. Precipitating protons, in particular, can occasionally produce ionization comparable to that produced by precipitating electrons. Measurements of proton fluxes measured by the NOAA 6 satellite were used to estimate the ionization produced by protons. These estimates were compared with the results of measurements made simultaneously by the Chatanika radar. Calculations based on linear transport theory were found to reproduce the observed profiles fairly well. In sunlit conditions photoioniaztion can also produce continuous auroral E region ionization. Chatanika radar data were used to examine the dependence of this source on solar zenith angle and solar flux.