Comparison of ground-based optical observations of N2 second positive to N2+ first negative emission ratios with electron precipitation energies inferred from the Sondre Stromfjord radar

Optical emission ratios of the N2 Second Positive Group 0,0 band to N2+ First Negative Group 0,0 band were observed in the magnetic zenith at Sondre Stromfjord in parallel with radar observations of the electron density height profile. The dependence of the optical ratios on the inferred incident electron energies was investigated to assess whether the ratios could be used as an electron energy monitor. Analysis procedures were developed to minimize the effects of atmospheric scattering as well as spectral blending with other emission features. Two independent computational techniques for inferring the electron energies from the electron density profiles were compared and found to agree sufficiently well for the current study. The observed optical emission ratios were found to vary by less than 15% over the incident electron energy range from 2 to 12 keV. Comparisons were made with the ratios predicted by several auroral electron deposition models