Observations of upper tropospheric/lower stratospheric water vapor and its isotopes

Airborne observations of high‐resolution infrared absorption, recorded between 1978 and 2005, are used to retrieve column amounts of H 2 16 O, H 2 17 O, H 2 18 O and HDO. Observations span a wide range of years, seasons and latitudes, all made with essentially the same spectrometer system. A spectral optimal estimator fitting technique, SFIT2, has been used uniformly to analyze all the data. The latitudinal distributions of H 2 16 O, H 2 17 O and H 2 18 O are similar and much like those from other observations (e.g., SPARC (Kley et al., 2000)). The column of HDO above 13 km exhibits a distribution with latitude that is much less pronounced. From 1978 to 2005 the long‐term increase in the column of Northern Hemisphere H 2 16 O above 13 km is found to be 1.16 ± 0.4%/year, consistent with previous observations. HDO is found to decrease by about 0.4%/year during the same period. In low latitudes, from 35°S to 35°N, large depletions of HDO relative to H 2 16 O, δD (−460 ± 21‰), and H 2 18 O relative to H 2 16 O (−104 ± 47‰) are determined. δD shows an unexpected trend of enhanced depletion of about 5–6‰ per year for the period from 1978 to 2005.