Articles | Volume 17, issue 16
Atmos. Chem. Phys., 17, 9751–9760, 2017
Atmos. Chem. Phys., 17, 9751–9760, 2017

Research article 18 Aug 2017

Research article | 18 Aug 2017

Resolving the mesospheric nighttime 4.3 µm emission puzzle: comparison of the CO2(ν3) and OH(ν) emission models

Peter A. Panka1,2, Alexander A. Kutepov2,3, Konstantinos S. Kalogerakis4, Diego Janches2, James M. Russell5, Ladislav Rezac6, Artem G. Feofilov7, Martin G. Mlynczak8, and Erdal Yiğit1 Peter A. Panka et al.
  • 1Department of Physics and Astronomy, George Mason University, Fairfax, VA, USA
  • 2NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 3The Catholic University of America, Washington, DC, USA
  • 4Center for Geospace Studies, SRI International, Menlo Park, CA, USA
  • 5Center for Atmospheric Sciences, Hampton University, Hampton, VA, USA
  • 6Max Planck Institute for Solar System Research, Göttingen, Germany
  • 7Laboratoire de Météorologie Dynamique/IPSL/FX-Conseil, CNRS, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau, France
  • 8NASA Langley Research Center, Hampton, VA, USA

Abstract. In the 1970s, the mechanism of vibrational energy transfer from chemically produced OH(ν) in the nighttime mesosphere to the CO2(ν3) vibration, OH(ν) ⇒ N2(ν) ⇒ CO2(ν3), was proposed. In later studies it was shown that this "direct" mechanism for simulated nighttime 4.3 µm emissions of the mesosphere is not sufficient to explain space observations. In order to better simulate these observations, an additional enhancement is needed that would be equivalent to the production of 2.8–3 N2(1) molecules instead of one N2(1) molecule in each quenching reaction of OH(ν) + N2(0). Recently a new "indirect" channel of the OH(ν) energy transfer to N2(ν) vibrations, OH(ν) ⇒ O(1D) ⇒ N2(ν), was suggested and then confirmed in a laboratory experiment, where its rate for OH(ν = 9) + O(3P) was measured. We studied in detail the impact of the "direct" and "indirect" mechanisms on CO2(ν3) and OH(ν) vibrational level populations and emissions. We also compared our calculations with (a) the SABER/TIMED nighttime 4.3 µm CO2 and OH 1.6 and 2.0 µm limb radiances of the mesosphere–lower thermosphere (MLT) and (b) with ground- and space-based observations of OH(ν) densities in the nighttime mesosphere. We found that the new "indirect" channel provides a strong enhancement of the 4.3 µm CO2 emission, which is comparable to that obtained with the "direct" mechanism alone but assuming an efficiency that is 3 times higher. The model based on the "indirect" channel also produces OH(ν) density distributions which are in good agreement with both SABER limb OH emission observations and ground and space measurements. This is, however, not true for the model which relies on the "direct" mechanism alone. This discrepancy is caused by the lack of an efficient redistribution of the OH(ν) energy from higher vibrational levels emitting at 2.0 µm to lower levels emitting at 1.6 µm. In contrast, the new  indirect  mechanism efficiently removes at least five quanta in each OH(ν ≥ 5) + O(3P) collision and provides the OH(ν) distributions which agree with both SABER limb OH emission observations and ground- and space-based OH(ν) density measurements. This analysis suggests that the important mechanism of the OH(ν) vibrational energy relaxation in the nighttime MLT, which was missing in the emission models of this atmospheric layer, has been finally identified.

Short summary
Recently, theoretical and laboratory studies have suggested an additional nighttime channel of transfer of vibrational energy of OH molecules to CO2 in the mesosphere and lower thermosphere (MLT). We show that new mechanism brings modelled 4.3 μm emissions very close to the SABER/TIMED measurements. This renders new opportunities for the application of the CO2 4.3 μm observations in the study of the energetics and dynamics of the nighttime MLT.
Final-revised paper