Atmos. Chem. Phys. Discuss., 13, 25801-25825, 2013
www.atmos-chem-phys-discuss.net/13/25801/2013/
doi:10.5194/acpd-13-25801-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Technical Note: A simple procedure for removing temporal discontinuities in ERA-Interim upper stratospheric temperatures for use in nudged chemistry-climate model simulations
C. McLandress1, D. A. Plummer2, and T. G. Shepherd3
1Department of Physics, University of Toronto, Toronto, Ontario, Canada
2Canadian Centre for Climate Modelling and Analysis, Victoria, British Columbia, Canada
3Department of Meteorology, University of Reading, Reading, Berkshire, UK

Abstract. This note describes a simple procedure for removing unphysical temporal discontinuities in ERA-Interim upper stratospheric temperatures in March 1985 and August 1998 that have arisen due to changes in satellite radiance data used in the assimilation. The derived adjustments (offsets) to the global mean temperatures are suitable for use in chemistry-climate models that are nudged to ERA-Interim winds and temperatures. Simulations using a nudged version of the Canadian Middle Atmosphere Model (CMAM) show that the inclusion of the temperature adjustments produces temperature time series that are devoid of the large jumps in 1985 and 1998. Due to its strong temperature dependence, the simulated upper stratospheric ozone is also shown to vary smoothly in time, unlike in a nudged simulation without the adjustments where abrupt changes in ozone occur at the times of the temperature jumps. While the adjustments to the ERA-Interim temperatures remove significant artefacts in the nudged CMAM simulation, spurious transient effects that arise due to water vapour and persist for about five years after the 1979 switch to ERA-Interim data are identified, underlining the need for caution when analysing trends in runs nudged to reanalyses.

Citation: McLandress, C., Plummer, D. A., and Shepherd, T. G.: Technical Note: A simple procedure for removing temporal discontinuities in ERA-Interim upper stratospheric temperatures for use in nudged chemistry-climate model simulations, Atmos. Chem. Phys. Discuss., 13, 25801-25825, doi:10.5194/acpd-13-25801-2013, 2013.
 
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