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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 6 | Copyright
Atmos. Chem. Phys., 17, 4177-4187, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 28 Mar 2017

Research article | 28 Mar 2017

Measuring FeO variation using astronomical spectroscopic observations

Stefanie Unterguggenberger1, Stefan Noll1, Wuhu Feng2,3, John M. C. Plane2, Wolfgang Kausch4,1, Stefan Kimeswenger5,1, Amy Jones6,1, and Sabine Moehler7 Stefanie Unterguggenberger et al.
  • 1Institut für Astro- und Teilchenpyhsik, Universität Innsbruck, Technikerstr. 25/8, 6020 Innsbruck, Austria
  • 2School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS 9JT, UK
  • 3National Centre for Atmospheric Science, University of Leeds, Woodhouse Lane, Leeds, LS 9JT, UK
  • 4Institute for Astrophysics, University of Vienna, Türkenschanzstr. 17, 1180 Vienna, Austria
  • 5Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile
  • 6Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
  • 7European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

Abstract. Airglow emission lines of OH, O2, O and Na are commonly used to probe the MLT (mesosphere–lower thermosphere) region of the atmosphere. Furthermore, molecules like electronically excited NO, NiO and FeO emit a (pseudo-) continuum. These continua are harder to investigate than atomic emission lines. So far, limb-sounding from space and a small number of ground-based low-to-medium resolution spectra have been used to measure FeO emission in the MLT. In this study the medium-to-high resolution echelle spectrograph X-shooter at the Very Large Telescope (VLT) in the Chilean Atacama Desert (24°37′S, 70°24′W; 2635m) is used to study the FeO pseudo-continuum in the range from 0.5 to 0.72µm based on 3662 spectra. Variations of the FeO spectrum itself, as well as the diurnal and seasonal behaviour of the FeO and Na emission intensities, are reported. These airglow emissions are linked by their common origin, meteoric ablation, and they share O3 as a common reactant. Major differences are found in the main emission peak of the FeO airglow spectrum between 0.58 and 0.61µm, compared with a theoretical spectrum. The FeO and Na airglow intensities exhibit a similar nocturnal variation and a semi-annual seasonal variation with equinoctial maxima. This is satisfactorily reproduced by a whole atmosphere chemistry climate model, if the quantum yields for the reactions of Fe and Na with O3 are 13±3 and 11±2% respectively. However, a comparison between the modelled O3 in the upper mesosphere and measurements of O3 made with the SABER satellite instrument suggests that these quantum yields may be a factor of ∼2 smaller.

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This study focuses on the analysis of astronomical medium-resolution spectra from the VLT in Chile to measure airglow pseudo-continuum emission of FeO in the optical regime. Compared to OH or Na emissions, this emission is difficult to measure. Using 3.5 years of spectroscopic data, we found annual and semi-annual variations of the FeO emission. Furthermore, we used WACCM to determine the quantum yield of the FeO-producing Fe + O3 reaction in the atmosphere, which has not been done before.
This study focuses on the analysis of astronomical medium-resolution spectra from the VLT in...