1Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Institut für Physik der Atmosphäre, Münchner Straße 20, Oberpfaffenhofen, 82234 Weßling, Germany
2Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Section Paleoclimate Dynamics, Bussestrasse 24, 27570 Bremerhaven, Germany
3Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Hermann-von-Helmholtz-Platz 1, 76344 Leopoldshafen, Germany
Received: 07 Aug 2014 – Discussion started: 16 Sep 2014
Abstract. 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 H218O and their physical fractionation processes. Additionally an explicit computation of the contribution of methane oxidation to H2O 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 CH3D 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.
Revised: 18 Apr 2015 – Accepted: 25 Apr 2015 – Published: 21 May 2015
Eichinger, R., Jöckel, P., Brinkop, S., Werner, M., and Lossow, S.: Simulation of the isotopic composition of stratospheric water vapour – Part 1: Description and evaluation of the EMAC model, Atmos. Chem. Phys., 15, 5537-5555, doi:10.5194/acp-15-5537-2015, 2015.