CO2(v2)-O quenching rate coefficient derived from coincidental SABER/TIMED and Fort Collins lidar observations of the mesosphere and lower thermosphere

Among the processes governing the energy balance in the mesosphere and lower thermosphere (MLT), the quenching of CO₂(v₂) vibrational levels by collisions with O atoms plays an important role. However, there is a factor of 3-4 discrepancy between the laboratory measurements of the CO₂-O quenching rate coefficient, kVT, and its value estimated from the atmospheric observations. In this study, we retrieve kVT in the altitude region 85-105 km from the coincident SABER/TIMED and Fort Collins sodium lidar observations by minimizing the difference between measured and simulated broadband limb 15 μm radiation. The averaged kVT value obtained in this work is 6.5 ± 1.5 × 10-12 cm3 s⁻¹ that is close to other estimates of this coefficient from the atmospheric observations. However, the retrieved kVT also shows altitude dependence and varies from 5.5 ± 1.1 × 10-12 cm3 s⁻¹ at 90 km to 7.9 ± 1.2 × 10-12 cm³ s⁻¹ at 105 km. Obtained results demonstrate the deficiency in current non-LTE modeling of the atmospheric 15 μm radiation, based on the application of the CO₂-O quenching and excitation rates, which are linked by the detailed balance relation. We discuss the possible model improvements, among them accounting for the interaction of the "non-thermal" oxygen atoms with CO₂ molecules.