Dependence of auroral middle UV emissions on the incident electron spectrum and neutral atmosphere

Abstract

In this paper we examine the relationship between three important middle UV auroral emissions, the electron energy spectrum, and the neutral atmosphere. We display calculated emission rates for the Vegard‐Kaplan and second positive band systems of N 2 and the O I (¹ S → ³ P ) 2972 Å line. All three features are proportional to the incoming energy flux, but they have different dependences on the characteristic energy of the incident electron spectrum and on the concentration of atomic oxygen. Therefore, in principle, observations of the intensities of these three emission features could be used to characterize the incident electron spectrum. Unfortunately, uncertainties in the chemistry of the ¹ S state of atomic oxygen and the A ³Σ u + state of nitrogen make it difficult to use such observations quantitatively. We discuss these uncertainties and possible alternative far ultraviolet features such as O I 1356 Å and 1304 Å and the N 2 Lyman‐Birge‐Hopfield bands.