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Published 2010 | Supplemental Material + Published
Journal Article Open

Trend in ice moistening the stratosphere – constraints from isotope data of water and methane


Water plays a major role in the chemistry and radiative budget of the stratosphere. Air enters the stratosphere predominantly in the tropics, where the very low temperatures around the tropopause constrain water vapour mixing ratios to a few parts per million. Observations of stratospheric water vapour show a large positive long-term trend, which can not be explained by change in tropopause temperatures. Trends in the partitioning between vapour and ice of water entering the stratosphere have been suggested to resolve this conundrum. We present measurements of stratospheric H_(2)O, HDO, CH_4 and CH_(3)D in the period 1991–2007 to evaluate this hypothesis. Because of fractionation processes during phase changes, the hydrogen isotopic composition of H_(2)O is a sensitive indicator of changes in the partitioning of vapour and ice. We find that the seasonal variations of H_(2)O are mirrored in the variation of the ratio of HDO to H_(2)O with a slope of the correlation consistent with water entering the stratosphere mainly as vapour. The variability in the fractionation over the entire observation period is well explained by variations in H_(2)O. The isotopic data allow concluding that the trend in ice arising from particulate water is no more than (0.01±0.13) ppmv/decade in the observation period. Our observations suggest that between 1991 and 2007 the contribution from changes in particulate water transported through the tropopause plays only a minor role in altering in the amount of water entering the stratosphere.

Additional Information

© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 30 June 2009; published in Atmos. Chem. Phys. Discuss.: 12 August 2009; revised: 14 December 2009; accepted: 15 December 2009; published: 12 January 2010. This research was financially supported by the EU-project SCOUT and by the national Helmholtz Association within the virtual institute PEP. We gratefully acknowledge Robert Toth (JPL/NASA, Pasadena) for updates of the H2O and HDO spectral line list. We thank the Columbia Scientific Balloon Facility (CSBF) who launched the balloons from which the MkIV data were acquired and the financial support from NASA. We acknowledge Jean-Francois Blavier, Bhaswar Sen, and David Petterson of JPL for their various contributions to the JPL MkIV instrument.

Attached Files

Published - Notholt2010p7131Atmos_Chem_Phys.pdf

Supplemental Material - acp-10-201-2010-supplement.pdf


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