Analysis of the N⁺₂ first negative band system in the Earth's upper atmosphere dayglow

Abstract

The First Negative (1N) band emission of the molecular nitrogen ion, N⁺₂ , is one of the most prominent features of the terrestrial dayglow spectrum. However, past N⁺₂ studies have encountered problems in validating the intensity of this emission. Also, some anomalous characteristics of the dayglow 1N spectrum remain unexplained, such as a highly developed rotational and vibrational structure. These anomalies appear to be due to the charge exchange reaction: O⁺ + N₂ → N⁺₂ + O, which dominates N⁺₂ ion production at high altitudes. This thesis examines dayglow 1N spectra acquired by the Arizona Airglow Experiment (GLO) flown on the space shuttle mission STS-74. In the analysis the emission is separated into two components. First is the emission from ions produced by photoionization and electron bombardment. Second is emission from ions produced by the charge exchange reaction, which cannot be modeled. The first source is evaluated and subtracted from the observed spectrum. The remaining emission is then used to derive empirical parameters related to the charge exchange reaction. These parameters can be used to estimate the 1N emission rate expected from the thermosphere, based on model atmosphere predictions. This emission rate can be used to determine the dayside O⁺ concentration using the GLO observations.