Assessment of the consistency of H2O line intensities over the near-infrared using sun-pointing ground-based Fourier transform spectroscopy |
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Authors: | L Tallis M Coleman IV Ptashnik KP Shine |
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Institution: | a Department of Meteorology, University of Reading, Reading, UK b National Physical Laboratory, Teddington, UK c V.E. Zuev Institute of Atmospheric Optics, SB Russian Academy of Science, Tomsk, Russia |
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Abstract: | We report on the consistency of water vapour line intensities in selected spectral regions between 800-12,000 cm−1 under atmospheric conditions using sun-pointing Fourier transform infrared spectroscopy. Measurements were made across a number of days at both a low and high altitude field site, sampling a relatively moist and relatively dry atmosphere. Our data suggests that across most of the 800-12,000 cm−1 spectral region water vapour line intensities in recent spectral line databases are generally consistent with what was observed. However, we find that HITRAN-2008 water vapour line intensities are systematically lower by up to 20% in the 8000-9200 cm−1 spectral interval relative to other spectral regions. This discrepancy is essentially removed when two new linelists (UCL08, a compilation of linelists and ab-initio calculations, and one based on recent laboratory measurements by Oudot et al. (2010) 10] in the 8000-9200 cm−1 spectral region) are used. This strongly suggests that the H2O line strengths in the HITRAN-2008 database are indeed underestimated in this spectral region and in need of revision. The calculated global-mean clear-sky absorption of solar radiation is increased by about 0.3 W m−2 when using either the UCL08 or Oudot line parameters in the 8000-9200 cm−1 region, instead of HITRAN-2008. We also found that the effect of isotopic fractionation of HDO is evident in the 2500-2900 cm−1 region in the observations. |
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Keywords: | Atmospheric absorption Fourier transform infrared spectroscopy HITRAN UCL08 line list Oudot line list Water vapour |
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