A Comparative Analysis of the OI 130.4-nm Emission Observed by NASA's TIMED Mission Using a Monte Carlo Radiative Transfer Model

Remote sensing of the OI 130.4-nm emission is potentially a useful means for routine monitoring of the atomic oxygen abundance in the upper atmosphere, especially for altitudes above similar to 300 km where the OI 135.6-nm emission becomes too dim to be useful. However, to date, the interpretation of the OI 130.4-nm emission as a proxy for the O density remains ambiguous in that the relative contribution of the external and internal sources to the production of this emission has not been fully understood. In this study, we perform a comparative analysis of the OI 130.4-nm dayglow observed by NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission using a Monte Carlo radiative transfer model to investigate the consistency between models and the TIMED/Global UltraViolet Imager (GUVI) data. The solar 130.4-nm flux is measured by TIMED/Solar EUV Experiment (SEE). The Global Airglow (GLOW) and the Atmospheric Ultraviolet Radiance Integrated Code (AURIC) models are used to calculate the initial volume emission rates due to photoelectron impact excitation, and the NRLMSISE-00 model is used to provide the atmospheric density and temperature profiles. Our data-model comparisons suggest that the model predicted contributions from photoelectron impact excitation need to be scaled by a factor of similar to 0.1-0.5 to achieve good fits with the data. Moreover, the modeled solar contributions need to be scaled up/down to fit the observations at small (similar to 20)/large (similar to 60) solar zenith angles, with a factor of similar to 0.5-1.7. These scale factors are larger than the uncertainties in the GUVI and SEE instrument calibrations, which might suggest inaccurate model predictions of the dayside O density and temperature variations with solar zenith angles. Plain Language Summary The OI 130.4-nm emission is one of the most prominent features in the far ultraviolet spectrum of Earth, Mars, and Venus. It has long been hoped that this bright airglow emission could be used to probe the atomic oxygen abundance in the upper atmosphere of terrestrial planets, where atomic oxygen is one of the key neutral species. However, owing to the very large opacity of the atmospheres to the OI 130.4-nm resonant lines, interpretation of their observations is very challenging. In this study, we develop a radiative transfer model for the calculation of the OI 130.4-nm emission in planetary atmospheres. The model is first validated and then applied to analyze the OI 130.4-nm emission observed by NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics mission. Data-model comparisons show that our current understanding of the relative contribution of different source mechanisms to the production of the OI 130.4-nm emission is not accurate and that refined models are needed to enable accurate remote sensing of the atomic oxygen density using the OI 130.4-nm emission in space missions.