CO2([nu]2)-O quenching rate coefficient derived from coincidental SABER/TIMED and Fort Collins lidar observations of the mesosphere and lower thermosphere

Abstract

Among the processes governing the energy balance in the mesosphere and lower thermosphere (MLT), the quenching of CO₂ (ν₂ ) 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, k_VT , and its value estimated from the atmospheric observations. In this study, we retrieve k_VT 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 k_VT 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 k_VT 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.

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