Auroral electrons and the optical emissions of nitrogen

The differential flux of auroral primary and secondary electrons and the emission of the 1 PG and 2 PG (first and second positive) systems of N2 and the 1 NG (first negative) system of N2+ were measured in a rocket experiment during a steady IBC II+ aurora. The electron data indicate that the incident auroral electrons were nearly monoenergetic with energy of about 25 keV. A single power law of the form F = F0Eα cannot accurately describe the secondary electron spectrum in the energy range of 3–85 eV. However, the spectrum may be approximated by using α = −3.2 between 7 and 20 eV and α = −0.9 between 25 and 85 eV. The measured intensity and altitude profile of the N2 1 PG (5, 2) band at 6685 Å agree well with the values calculated by using the measured electron flux and laboratory cross-section data. About 40% of the N2+ 1 NG (0, 0) band emission at 3914 Å is excited by electrons with energy below 85 eV.