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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 05 Aug 2019

Submitted as: research article | 05 Aug 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Description and Evaluation of the Specified-Dynamics Experiment in the Chemistry-Climate Model Initiative (CCMI)

Clara Orbe1, David A. Plummer2, Darryn W. Waugh3, Huang Yang3,4, Patrick Jöckel5, Douglas E. Kinnison6, Beatrice Josse7, Virginie Marecal7, Makoto Deushi8, Nathan Luke Abraham9,10, Alexander T. Archibald9,10, Martyn P. Chipperfield11, Sandip Dhomse11, Wuhu Feng10,11, and Slimane Bekki12 Clara Orbe et al.
  • 1NASA Goddard Institute for Space Studies, New York, NY, USA
  • 2Climate Research Branch, Environment and Climate Change Canada, Montreal, QC, Canada
  • 3Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland, USA
  • 4Department of Atmospheric and Ocean Sciences, University of California, Los Angeles
  • 5Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 6National Center for Atmospheric Research (NCAR), Atmospheric Chemistry Observations and Modeling (ACOM) Laboratory, Boulder, USA
  • 7Centre National de Recherches Météorologiques UMR 3589, Météo-France/CNRS, Toulouse, France
  • 8Meteorological Research Institute (MRI), Tsukuba, Japan
  • 9Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK
  • 10National Centre for Atmospheric Science, UK
  • 11School of Earth and Environment, University of Leeds, Leeds, UK
  • 12Laboratoire de Météorologie Dynamique (LMD/IPSL)

Abstract. Here we provide an overview of the REF-C1SD Specified-Dynamics experiment that was conducted as part of Phase 1 of the Chemistry-Climate Model Initiative (CCMI). The REF-C1SD experiment, which consisted of mainly online general circulation models (GCMs) constrained with (re)analysis fields, was designed to examine the influence of the large-scale circulation on past trends in atmospheric composition. The REF-C1SD simulations were produced across various model frameworks and we evaluate how well the simulations represent different measures of the dynamical and transport circulations. In the troposphere there are large (~ 40 %) differences in the climatological mean distributions and seasonal cycle amplitude of the meridional and vertical winds. In the stratosphere there are similarly large (~ 50 %) differences in the magnitude and seasonal cycle amplitude of the Transformed Eulerian Mean circulation and among various chemical and idealized tracers. For nearly all variables these differences are not related to the use of different reanalysis products; rather, we show they are associated with how the simulations were implemented, by which we refer both to how the large-scale flow was prescribed and to biases in the underlying free-running models. Furthermore, in most cases these differences are shown to be as large or even larger than the differences exhibited by free-running simulations produced using the exact same models. Overall, our results suggest that care must be taken when using specified-dynamics simulations to examine the influence of large-scale dynamics on composition.

Clara Orbe et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Clara Orbe et al.
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Publications Copernicus
Short summary
Atmospheric composition is strongly influenced by global-scale winds that are not always properly simulated in computer models. A common approach to correct for this bias is to relax or nudge to the observed winds. Here we systematically evaluate how well this technique performs across a large suite of chemistry climate models in terms of its ability to reproduce key aspects of both the tropospheric and stratospheric circulations.
Atmospheric composition is strongly influenced by global-scale winds that are not always...