Atomic nitrogen in aurora: Production, chemistry, and optical emissions

Abstract

The production of ground configuration nitrogen atoms in aurora is investigated. The two principal mechanisms are electron impact dissociation of N2 and chemical‐ionic reactions, with the latter dominating the production of N(²D). Between 60 and 70% of the N atoms are produced in the excited ²P and ²D states over a large altitude range. Simultaneous field‐aligned measurements of the 5200‐Å and 3466‐Å lines of N I and the 4278‐Å first negative group band of N2+ were made in the northern nightside auroral oval under varying auroral conditions. These data, taken over a continuous 4‐hour period on the night of February 5, 1978, yield an average emission rate ratio of the 5200‐Å/3466‐Å lines near 0.5. Model calculations yield ratios of 0.5 and 1.4 for particle characteristic energies (alpha) of 2 keV and 0.1 keV in an assumed Maxwellian electron spectrum in good agreement with the observations reported here and consistent with those reported in the literature for very soft precipitation in the dayside cusp region. The production rate of energetic (hot) N(4S) atoms in the aurora is evaluated from considerations of the excess translational energy associated with N atom production. It may be a significant factor in the production rate of NO and the odd nitrogen density in general in the auroral atmosphere.