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Simpson, I. R.; Hitchcock, P.; Shepherd, T. G.; Scinocca, J. F. (2011)
Publisher: American Geophysical Union
Languages: English
Types: Article
Climate models tend to exhibit much too persistent Southern Annular Mode (SAM) circulation anomalies in summer, compared to observations. Theoretical arguments suggest this bias may lead to an overly strong model response to anthropogenic forcing during this season, which is of interest since the largest observed changes in Southern Hemisphere high‐latitude climate over the last few decades have occurred in summer, and are congruent with the SAM. The origin of this model bias is examined here in the case of the Canadian Middle Atmosphere Model, using a novel technique to quantify the influence of stratospheric variability on tropospheric annular‐mode timescales. Part of the model bias is shown to be attributable to the too‐late breakdown of the stratospheric polar vortex, which allows the tropospheric influence of stratospheric variability to extend into early summer. However, the analysis also reveals an enhanced summertime persistence of the model’s SAM that is unrelated to either stratospheric variability or the bias in model stratospheric climatology, and is thus of tropospheric origin. No such feature is evident in the Northern Hemisphere. The effect of stratospheric variability in lengthening tropospheric annular‐mode timescales is evident in both hemispheres. While in the Southern Hemisphere the effect is restricted to late‐spring/early summer, in the Northern Hemisphere it can occur throughout the winter‐spring season, with the seasonality of peak timescales exhibiting considerable variability between different 50 year sections of the same simulation.
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    • Baldwin, M. P., and D. W. J. Thompson (2009), A critical comparison of stratosphere‐troposphere coupling indices, Q. J. R. Meteorol. Soc., 135, 1661-1672.
    • Baldwin, M. P., D. B. Stephenson, D. W. J. Thompson, T. J. Dunkerton, A. J. Charlton, and A. O'Neill (2003), Stratospheric memory and skill of extended‐range weather forecasts, Science, 301, 636-640, doi:10.1126/ science.1087143.
    • Butchart, N., et al. (2011), Multimodel climate and variability of the stratosphere, J. Geophys. Res., 116, D05102, doi:10.1029/2010JD014995.
    • Dee, D. P., et al. (2011), The ERA‐interim reanalysis: Configuration and performance of the data assimilation system, Q. J. R. Meteorol. Soc., 137, 553-597, doi:10.1002/qj.828.
    • Fogt, R. L., J. Perlwitz, A. J. Monaghan, D. H. Bromwich, J. M. Jones, and G. J. Marshall (2009), Historical SAM variability. Part II: Twentiethcentury variability and trends from reconstructions, observations, and the IPCC AR4 models, J.Clim., 22, 5346-5365, doi:10.1175/ 2009JCLI2786.1.
    • Fyfe, J. C., and O. A. Saenko (2006), Simulated changes in the extratropical Southern Hemisphere winds and currents, Geophys. Res. Lett., 33, L06701, doi:10.1029/2005GL025332.
    • Gerber, E. P., and L. M. Polvani (2009), Stratosphere‐troposphere coupling in a relatively simple AGCM: The importance of stratospheric variability, J. Clim., 22, 1920-1933.
    • Gerber, E. P., L. M. Polvani, and D. Ancukiewicz (2008), Annular mode time scales in the Intergovernmental Panel on Climate Change Fourth Assessment Report models, Geophys. Res. Lett., 35, L22707, doi:10.1029/2008GL035712.
    • Gerber, E. P., et al. (2010), Stratosphere‐troposphere coupling and annular mode variability in chemistry‐climate models, J. Geophys. Res., 115, D00M06, doi:10.1029/2009JD013770.
    • Keeley, S. P. E., R. T. Sutton, and L. C. Shaffrey (2009), Does the North Atlantic Oscillation show unusual persistence on intraseasonal timescales?, Geophys. Res. Lett., 36, L22706, doi:10.1029/2009GL040367.
    • Kidston, J., and E. P. Gerber (2010), Intermodel variability of the poleward shift of the austral jet stream in the CMIP3 integrations linked to biases in 20th century climatology, Geophys. Res. Lett., 37, L09708, doi:10.1029/2010GL042873.
    • Kushner, P. J. (2010), Annular modes of the troposphere and stratosphere, in The Stratosphere: Dynamics, Transport, and Chemistry, Geophys. Monogr. Ser., vol. 190, edited by L. M. Polvani, A. H. Sobel, and D. W. Waugh, pp. 59-91, AGU, Washington, D. C., doi:10.1029/ 2009GM000924.
    • Lorenz, D. J., and D. L. Hartmann (2001), Eddy‐zonal flow feedback in the Southern Hemisphere, J. Atmos. Sci., 58, 3312-3327.
    • Miller, R. L., G. A. Schmidt, and D. T. Shindell (2006), Forced annular variations in the 20th century Intergovernmental Panel on Climate Change Fourth Assessment Report models, J. Geophys. Res., 111, D18101, doi:10.1029/2005JD006323.
    • Mudryk, L. R., and P. J. Kushner (2011), A method to diagnose sources of annular mode time scales, J. Geophys. Res., 116, D14114, doi:10.1029/ 2010JD015291.
    • Norton, W. A. (2003), Sensitivity of Northern Hemisphere surface climate to simulation of the stratospheric polar vortex, Geophys. Res. Lett., 30(12), 1627, doi:10.1029/2003GL016958.
    • Ring, M. J., and R. A. Plumb (2008), The response of a simplified GCM to axisymmetric forcings: Applicability of the fluctuation-dissipation theorem, J. Atmos. Sci., 65, 3880-3898.
    • Scinocca, J. F., N. A. McFarlane, M. Lazare, J. Li, and D. Plummer (2008), Technical note: The CCCma third generation AGCM and its extension into the middle atmosphere, Atmos. Chem. Phys., 8, 7055-7074.
    • Thompson, D. W. J., and J. M. Wallace (2000), Annular modes in the extratropical circulation. Part I: Month‐to‐month variability, J. Clim., 13, 1000-1016.
    • P. Hitchcock, T. G. Shepherd, and I. R. Simpson, Department of Physics, University of Toronto, 60 St. George St., Toronto, ON M5S 1A7, Canada.
    • () J. F. Scinocca, Canadian Centre for Climate Modelling and Analysis, Environment Canada, PO Box 3065 STN CSC,Victoria, BC V8W 3V6, Canada.
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