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The relative abundance of the heavy water isotopologue HDO provides a deeper insight into the atmospheric hydrological cycle. The SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) allows for global retrievals of the ratio HDO/HO in the 2.3 micron wavelength range. However, the spectroscopy of water lines in this region remains a large source of uncertainty for these retrievals. We therefore evaluate and improve the water spectroscopy in the range 4174–4300 cm⁻¹ and test if this reduces systematic uncertainties in the SCIAMACHY retrievals of HDO/H₂O. We use a laboratory spectrum of water vapour to fit line intensity, air broadening and wavelength shift parameters. The improved spectroscopy is tested on a series of ground-based high resolution FTS spectra as well as on SCIAMACHY retrievals of H2O and the ratio HDO/H₂O. We find that the improved spectroscopy leads to lower residuals in the FTS spectra compared to HITRAN 2008 and Jenouvrier et al. (2007) spectroscopy, and the retrievals become more robust against changes in the retrieval window. For both the FTS and SCIAMACHY measurements, the retrieved total H₂O columns decrease by 2–4% and we find a negative shift of the HDO/H₂O ratio, which for SCIAMACHY is partly compensated by changes in the retrieval setup and calibration software. The updated SCIAMACHY HDO/H₂O product shows somewhat steeper latitudinal and temporal gradients and a steeper Rayleigh distillation curve, strengthening previous conclusions that current isotope-enabled general circulation models underestimate the variability in the near-surface HDO/H₂O ratio.

This is the second of a series of articles reporting critically evaluated rotational-vibrational line positions, transition intensities, pressure dependences, and energy levels, with associated critically reviewed assignments and uncertainties, for all the main isotopologues of water. This article presents energy levels and line positions of the following singly deuterated isotopologues of water: HD16O, HD17O, and HD18O. The MARVEL (measured active rotational-vibrational energy levels) procedure is used to determine the levels, the lines, and their self-consistent uncertainties for the spectral regions 0-22708, 0-1674, and 0-12105cm-1 for HD16O, HD17O, and HD18O, respectively. For HD16O, 54740 transitions were analyzed from 76 sources, the lines come from spectra recorded both at room temperature and from hot samples. These lines correspond to 36690 distinct assignments and 8818 energy levels. For HD17O, only 485 transitions could be analyzed from three sources; the lines correspond to 162 MARVEL energy levels. For HD18O, 8729 transitions were analyzed from 11 sources and these lines correspond to 1864 energy levels. The energy levels are checked against ones determined from accurate variational nuclear motion computations employing exact kinetic energy operators. This comparison shows that the measured transitions account for about 86% of the anticipated absorbance of HD16O at 296K and that the transitions predicted by the MARVEL energy levels account for essentially all the remaining absorbance. The extensive list of MARVEL lines and levels obtained are given in the Supplementary Material of this article, as well as in a distributed information system applied to water, W@DIS, where they can easily be retrieved. In addition, the transition and energy level information for H217O and H218O, given in the first paper of this series [Tennyson, et al. J Quant Spectr Rad Transfer 2009;110:573-96], has been updated. © 2010 Elsevier Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published

Laboratory absorption spectra of H2O-D2O mixtures have been recorded in the spectral region 8800-1500 cm-1 by Fourier transform spectroscopy at high resolution (0.03 cm-1 ). The 50 m base long cell from Reims was used to record spectra with total pressure £ absorption path products of about 6000 torr m. In the continuation of our previous work concerning water vapor 1 ; 2 ; 3 ; 4 ; 5 ; 6 ; 7 ; 8 ; 9 ; 10 , the present study deals with the Deuterium enriched spectra. Two spectra with diÆerent mixing ratios for H 2 O, HDO and D 2 O species were recorded. The identiØcation of the HDO and D 2 O lines has been made by comparison of ratios between pure and enriched spectra. Partial pressures were carefully determined using (i) H2 ^16O previously determined line intensities, (ii) HDO and D 2 O line intensity ratios, and (iii) total pressures. The lines identiØcation was checked through the evolution of the integrated absorption coe±cients with the partial pressures. The observed lines have been Øtted to Voigt line proØles from which line positions (cali- brated afterwards), integrated absorption cross-sections and self-broadening coe±cients have been determined. For the two deuterated species the integrated absorption cross sections could be measured down to 5 10-27 cm/molecule. Comparisons with the most recent experimental data and calculations are presented.

Line parameters for water vapour in natural abundance have recently been determined for the 9250-13 000 cm(-1) region [M.-F. Wrienne, A. Jenouvrier, C. Hermans, A.C. Vandaele, M. Carleer, C. Clerbaux, P.-F. Coheur, R. Colin, S. Fally, M. Bach, J. Quant. Spectrosc. Radiat. Transfer 82 (2003) 99] and the 13 000-26 000 cm(-1) region [P.-F. Coheur, S. Fally, M. Carleer, C. Clerbaux, R. Colin, A. Jenouvrier, M.-F. Wrienne, C. Hermans, A.C. Vandaele, J. Quant. Spectrosc. Radial. Transfer 74 (2002) 493] using a high-resolution Fourier-transform spectrometer with a long-path absorption cell. These spectra are analysed using several techniques including variational line lists and assignments made. In total, over 15 000 lines were assigned to transitions involving more than 150 exited vibrational states of (H2O)-O-16. Twelve new vibrational band origins are determined and estimates for a further 16 are presented. (c) 2005 Elsevier Inc. All rights reserved.