CO2(v2)-O Quenching Rate Coefficient Derived From Coincidental SABER/TIMED And Ground-Based Lidar Observations Of The Mesosphere And Lower Thermosphere

Infrared emission in 15 μm CO2 band (I15 μm) is the dominant cooling mechanism in the Earth's mesosphere and lower thermosphere (MLT). On Earth, the magnitude of the MLT cooling affects both the mesopause temperature and height; the stronger the cooling, the colder and higher is the mesopause. This process is also important for the energy budgets of Martian and, especially, Venusian atmospheres, where CO2 cooling compensates for the EUV heating of the dayside upper atmosphere. The I15 μm radiation is used to retrieve vertical temperature distributions T(z) in Earth's atmosphere by a number of satellite instruments. Both the cooling efficiency and I15 μm strongly depend on the rate coefficient of the quenching of the CO2(ν2) vibrational levels by collisions with oxygen atoms. However, there is a factor of 3-4 discrepancy between the laboratory measurements of this 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 ground-based lidar observations in different locations by minimizing the difference between measured and simulated broadband limb 15 μm radiation. 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.