Determination of the energy of auroral electrons by the measurements of the emission ratio and altitude of aurorae

Abstract

The energy of auroral electrons has been determined by two independent methods. First, the altitude of discrete auroral forms has been estimated from two all-sky camera pictures using an iterative method. The altitudes have been converted to energies using the theories of electron penetration into the atmosphere. Secondly, the intensity ratio of 630.0 and 427.8 nm emissions has been measured from the same auroral forms. The emission ratio energy has been derived from theoretical emission ratio calculations. Using these methods the two energies have been compared in about 140 cases. The emission ratio energies calculated on the basis of the monoenergetic electron flux theory by Vallance Jones (1975, Can. J. Phys. 53, 2267) are in the best agreement with the electron penetration theory by Banks et al. (1974, J. geophys. Res. 79, 1459). By using Maxwellian electron flux the emission ratio model by Rees and Luckey (1974, J. geophys. Res. 79, 5181) gives too high characteristic energies as compared with electron penetration theories. The measured emission ratios and altitude energies of the same auroral arcs have also been fitted to cubic spline function. A new nomogram has been drawn where the altitude energy of auroral electrons in discrete arcs can be determined as a function of 427.8 nm intensity and 630.0 nm/427.8 nm intensity ratio.