CO2(ν2)-O quenching rate coefficient derived from coincidental SABER/TIMED and Fort Collins lidar observations of the mesosphere and lower thermosphere

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Feofilov, A. G. ; Kutepov, A. A. ; She, C.-Y. ; Smith, A. K. ; Pesnell, W. D. ; Goldberg, R. A. (2012)

Among the processes governing the energy balance in the mesosphere and lower thermosphere (MLT), the quenching of CO<sub>2</sub>(&nu;<sub>2</sub>) 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 CO<sub>2</sub>-O quenching rate coefficient, <i>k</i><sub>VT</sub>, and its value estimated from the atmospheric observations. In this study, we retrieve <i>k</i><sub>VT</sub> 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 <i>k</i><sub>VT</sub> value obtained in this work is 6.5 &plusmn; 1.5 &times; 10<sup>&minus;12</sup> cm<sup>3</sup> s<sup>−1</sup> that is close to other estimates of this coefficient from the atmospheric observations. However, the retrieved <i>k</i><sub>VT</sub> also shows altitude dependence and varies from 5.5 &plusmn; 1.1 &times; 10<sup>&minus;12</sup> cm<sup>3</sup> s<sup>−1</sup> at 90 km to 7.9 &plusmn; 1.2 &times; 10<sup>&minus;12</sup> cm<sup>3</sup> s<sup>−1</sup> 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 CO<sub>2</sub>-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 CO<sub>2</sub> molecules.
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