Technical Note: A simple procedure for removing temporal discontinuities in ERA-Interim upper stratospheric temperatures for use in nudged chemistry-climate model simulations 1Department of Physics, University of Toronto, Toronto, Ontario, Canada
12 Feb 2014
2Canadian Centre for Climate Modelling and Analysis, Victoria, British Columbia, Canada
3Department of Meteorology, University of Reading, Reading, Berkshire, UK
Received: 25 Jul 2013 – Published in Atmos. Chem. Phys. Discuss.: 08 Oct 2013 Abstract. This note describes a simple procedure for removing unphysical temporal
discontinuities in ERA-Interim upper stratospheric global mean temperatures
in March 1985 and August 1998 that have arisen due to changes in satellite
radiance data used in the assimilation. The derived temperature adjustments
(offsets) are suitable for use in stratosphere-resolving chemistry-climate
models that are nudged (relaxed) 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 5 yr after the 1979 switch to ERA-Interim data are identified, underlining
the need for caution when analysing trends in runs nudged to reanalyses.
Revised: 21 Dec 2013 – Accepted: 07 Jan 2014 – Published: 12 Feb 2014
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., 14, 1547-1555, doi:10.5194/acp-14-1547-2014, 2014.