Constraining the Upper Level Vibrational Populations of the N₂ Lyman-Birge-Hopfield Band System Using GOLD Mission's Dayglow Observations

Current and previous thermospheric remote sensing missions use N₂ Lyman-Birge-Hopfield (LBH) band dayglow emission measurements to retrieve line-of-sight thermospheric composition and temperature. The precision of thermospheric composition and temperature retrieved from observations depends on the uncertainty in the relative LBH vibrational populations. In the laboratory, electron impact induced LBH emission measurements have shown that the relative vibrational populations change with gas pressure. However, it is not fully understood how these populations change for dayglow observations where the emissions that contribute to the observations vary with solar illumination and line-of-sight geometry. We quantify the relative vibrational populations as a function of solar zenith angle (SZA) and tangent altitude using Global-scale Observations of Limb and Disk mission's LBH dayglow observations. We find that, while some lower vibrational levels show potential enhancement with increasing pressure (decreasing altitude), in general, they do not change significantly with SZA or tangent altitude for dayglow observations. The vibrational populations can thus be assumed as fixed parameters when retrieving neutral disk temperatures from remotely sensed LBH dayglow observations.