A posteriori calculation of δ 18O and δD in atmospheric water vapour from ground-based near-infrared FTIR retrievals of H 216O, H 218O, and HD 16O

Rokotyan, N. V.; Zakharov, V. I.; Gribanov, K. G.; Schneider, M.; Bréon, F.-M.; Jouzel, J.; Imasu, R.; Werner, M.; Butzin, M.; Petri, C.; Warneke, T.; Notholt, J.

This paper investigates the scientific value of retrieving H 218O and HDO columns in addition to H 216O columns from high-resolution ground-based near-infrared spectra. We present a set of refined H 216O, H 218O, and HDO spectral windows. The retrieved H 216O, H 218O, and HDO columns are used for an a posteriori calculation of columnar δD and δ 18O. We estimate the uncertainties for the so-calculated columnar δD and δ 18O values. These estimations include uncertainties due to the measurement noise, errors in the a priori data, and uncertainties in spectroscopic parameters. Time series of δ 18O obtained from ground-based FTIR (Fourier transform infrared) spectra are presented for the first time.

For our study we use a full physics isotopic general circulation model (ECHAM5-wiso). We show that the full physics simulation of HDO and H 218O can already be reasonably predicted from the H 216O columns by a simple linear regression model (scatter values between full physics and linear regression simulations are 35 and 4‰ for HDO and H 218O, respectively). We document that the columnar δD and δ 18O values as calculated a posteriori from the retrievals of H 216O, H 218O, and HDO show a better agreement with the ECHAM5-wiso simulation than the δD and δ 18O values as calculated from the H 216O retrievals and the simple linear regression model. This suggests that the H 218O and HDO column retrievals add complementary information to the H 216O retrievals. However, these data have to be used carefully, because of the different vertical sensitivity of the H 216O, H 218O, and HDO columnar retrievals. Furthermore, we have to note that the retrievals use reanalysis humidity profiles as a priori input and the results are thus not independent of the reanalysis data.

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Rokotyan, N. V. / Zakharov, V. I. / Gribanov, K. G. / et al: A posteriori calculation of δ18O and δD in atmospheric water vapour from ground-based near-infrared FTIR retrievals of H216O, H218O, and HD16O. 2014. Copernicus Publications.

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