Simulation of the isotopic composition of stratospheric water vapour – Part 1: Description and evaluation of the EMAC model
This modelling study aims at an improved understanding of the processes that determine the water vapour budget in the stratosphere by means of the investigation of water isotope ratios. An additional (and separate from the actual) hydrological cycle has been introduced into the chemistry–climate mod...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-05-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/15/5537/2015/acp-15-5537-2015.pdf |
| Summary: | This modelling study aims at an improved understanding of the processes that
determine the water vapour budget in the stratosphere by means of the
investigation of water isotope ratios. An additional (and separate
from the actual) hydrological cycle has been introduced into the
chemistry–climate model EMAC, including the water isotopologues HDO and
H<sub>2</sub><sup>18</sup>O and their physical fractionation processes. Additionally an
explicit computation of the contribution of methane oxidation to H<sub>2</sub>O and
HDO has been incorporated. The model expansions allow detailed analyses of
water vapour and its isotope ratio with respect to deuterium throughout the
stratosphere and in the transition region to the troposphere. In order to
assure the correct representation of the water isotopologues in the model's
hydrological cycle, the expanded system has been evaluated in several steps.
The physical fractionation effects have been evaluated by comparison of the
simulated isotopic composition of precipitation with measurements from a
ground-based network (GNIP) and with the results from the
isotopologue-enabled general circulation model ECHAM5-wiso. The model's
representation of the chemical HDO precursor CH<sub>3</sub>D in the stratosphere has
been confirmed by a comparison with chemical transport models (1-D, CHEM2D)
and measurements from radiosonde flights. Finally, the simulated
stratospheric HDO and the isotopic composition of water vapour have been
evaluated, with respect to retrievals from three different satellite
instruments (MIPAS, ACE-FTS, SMR). Discrepancies in stratospheric water
vapour isotope ratios between two of the three satellite retrievals can now
partly be explained. |
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| ISSN: | 1680-7316 1680-7324 |