Self‐absorption theory applied to rocket measurements of the nitric oxide (1, 0) γ band in the daytime thermosphere

Abstract

Sounding rocket observations of the ultraviolet fluorescent emissions of the nitric oxide molecule in the lower thermospheric dayglow are described and analyzed. The rocket experiment was an ultraviolet spectrometer which took limb‐viewing spectra of the dayglow between 90‐ and 185‐km altitude in the spectral region from 2120 to 2505 Å with a resolution of 2.0 Å. The flight occurred at local noon on March 7, 1989, from Poker Flat, Alaska. Several NO γ bands were visible at all altitudes of the flight, along with emission features of N2, O+, and N+. The data for the NO (1, 0) and (0, 1) γ bands were modeled with optically thin synthetic spectra and used as diagnostics of nitric oxide concentrations. The resonant NO (1, 0) γ band emissions were shown to be attenuated at low altitudes relative to the expected emission rates predicted from comparison with the nonresonant (0, 1) γ band. Inversion of the optically thin data resulted in a peak nitric oxide concentration of 3.1 × 108 cm−3 at an altitude of 100 km. A self‐absorption model using Holstein transmission functions was developed and applied to the (1, 0) γ band observations. The model results agree with the measured attenuation of the band, indicating the necessity of including self‐absorption theory in the analysis of satellite and rocket limb data of NO. The success of the model also confirms the value adopted for the absorption oscillator strength of the (1, 0) γ band transition and the instrument calibration.