• Barnes, E. A., and D. L. Hartmann, 2011: Rossby wave scales, propagation, and the variability of eddy-driven jets. J. Atmos. Sci., 68, 28932908.

    • Search Google Scholar
    • Export Citation
  • Barnes, E. A., D. L. Hartmann, D. M. W. Frierson, and J. Kidson, 2010: The effect of latitude on the persistence of eddy-driven jets. Geophys. Res. Lett., 37, L11804, doi:10.1029/2010GL043199.

    • Search Google Scholar
    • Export Citation
  • Butler, A., D. W. J. Thompson, and R. Heikes, 2010: The steady-state atmospheric circulation response to climate change–like thermal forcings in a simple general circulation model. J. Climate, 23, 34743496.

    • Search Google Scholar
    • Export Citation
  • Chen, G., and P. Zurita-Gotor, 2008: The tropospheric jet response to prescribed zonal forcing in an idealized atmospheric model. J. Atmos. Sci., 65, 22542271.

    • Search Google Scholar
    • Export Citation
  • Chen, G., I. M. Held, and W. A. Robinson, 2007: Sensitivity of the latitude of the surface westerlies to surface friction. J. Atmos. Sci., 64, 28992915.

    • Search Google Scholar
    • Export Citation
  • DelSole, T., 2001: A simple model for transient eddy momentum fluxes in the upper troposphere. J. Atmos. Sci., 58, 30193035.

  • Dickinson, R. E., 1970: Development of a Rossby wave critical level. J. Atmos. Sci., 27, 627633.

  • Frierson, D. M. W., I. M. Held, and P. Zurita-Gotor, 2006: A gray-radiation aquaplanet moist GCM. Part I: Static stability and eddy scale. J. Atmos. Sci., 63, 25482566.

    • Search Google Scholar
    • Export Citation
  • Fyfe, J. C., G. J. Boer, and G. M. Flato, 1999: The Arctic and Antarctic oscillations and their projected changes under global warming. Geophys. Res. Lett., 26, 16011604.

    • Search Google Scholar
    • Export Citation
  • Haigh, J. D., M. Blackburn, and R. Day, 2005: The response of tropospheric circulation to perturbations in lower-stratospheric temperature. J. Climate, 18, 36723685.

    • Search Google Scholar
    • Export Citation
  • Holton, J., 1992: An Introduction to Dynamic Meteorology. 3rd ed. Academic Press, 511 pp.

  • Hoskins, B. J., and D. J. Karoly, 1981: The steady linear response of a spherical atmosphere to thermal and orographic forcing. J. Atmos. Sci., 38, 11791196.

    • Search Google Scholar
    • Export Citation
  • Hoskins, B. J., and T. Ambrizzi, 1993: Rossby wave propagation on a realistic longitudinally varying flow. J. Atmos. Sci., 50, 16611671.

    • Search Google Scholar
    • Export Citation
  • Kidston, J., and G. K. Vallis, 2010: Relationship between eddy-driven jet latitude and width. Geophys. Res. Lett., 37, L21809, doi:10.1029/2010GL044849.

    • Search Google Scholar
    • Export Citation
  • Kidston, J., D. M. W. Frierson, J. A. Renwick, and G. K. Vallis, 2010: Observations, simulations, and dynamics of jet stream variability and annular modes. J. Climate, 23, 61866199.

    • Search Google Scholar
    • Export Citation
  • Lorenz, D. J., and E. T. DeWeaver, 2007: Tropopause height and zonal wind response to global warming in the IPCC scenario integrations. J. Geophys. Res., 112, D10119, doi:10.1029/2006JD008087.

    • Search Google Scholar
    • Export Citation
  • Lu, J., G. Chen, and D. M. W. Frierson, 2010: The position of the midlatitude storm track and eddy-driven westerlies in aquaplanet AGCMs. J. Atmos. Sci., 67, 39844000.

    • Search Google Scholar
    • Export Citation
  • Meehl, G. A., and Coauthors, 2007a: Global climate projections. Climate Change 2007: The Physical Science Basis. S. Solomon et al., Eds., Cambridge University Press, 747–845.

  • Meehl, G. A., C. Covey, T. Delworth, M. Latif, B. McAvaney, J. F. B. Mitchell, R. J. Stouffer, and K. E. Taylor, 2007b: The WCRP CMIP3 multi-model dataset: A new era in climate change research. Bull. Amer. Meteor. Soc., 88, 13831394.

    • Search Google Scholar
    • Export Citation
  • Polvani, L. M., and P. J. Kushner, 2002: Tropospheric response to stratospheric perturbations in a relatively simple general circulation model. Geophys. Res. Lett., 29, 1114, doi:10.1029/2001GL014284.

    • Search Google Scholar
    • Export Citation
  • Robinson, W. A., 2006: On the self-maintenance of midlatitude jets. J. Atmos. Sci., 63, 21092122.

  • Vallis, G. K., E. P. Gerber, P. J. Kushner, and B. A. Cash, 2004: A mechanism and simple dynamical model of the North Atlantic oscillation and annular modes. J. Atmos. Sci., 61, 264280.

    • Search Google Scholar
    • Export Citation
  • Williams, G. P., 2006: Circulation sensitivity to tropopause height. J. Atmos. Sci., 63, 19541961.

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The Relationship between the Speed and the Latitude of an Eddy-Driven Jet in a Stirred Barotropic Model

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  • 1 Climate Change Research Centre, The University of New South Wales, Sydney, New South Wales, Australia, and Princeton University, Princeton, New Jersey
  • | 2 Princeton University, Princeton, New Jersey
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Abstract

A stirred barotropic model on a sphere is used to investigate the relationship between the speed and the latitude of an eddy-driven jet. When the wind speed is increased in the model, the jet shifts poleward, despite the fact that the stirring of vorticity remains statistically constant. The cause is found to be increasing meridional shear that results from increasing the wind speed in a meridionally confined region and reduces the absolute vorticity gradient on the flanks of the jet. This has two related consequences. The first is that wave propagation is discouraged, as a turning latitude is created where the absolute vorticity gradient tends to zero. On the sphere, this occurs first at high latitudes, thereby shifting wave dissipation toward the equator. The reduced high-latitude dissipation causes a poleward shift of the jet. The second consequence occurs when the vorticity gradient actually becomes negative, in which case the waves may overreflect where an instability is present, providing a high-latitude source of pseudomomentum. This may further encourage the jet to shift poleward.

The relevance of the barotropic dynamics to more realistic atmospheres is unclear, but the intermodel variability of the poleward shift of the jet in response to increasing CO2 across a suite of state-of-the-art GCMs is consistent with the barotropic dynamics, suggesting that further investigation is warranted.

Corresponding author address: J. Kidston, Climate Change Research Centre, Level 4 Matthew’s Building, University of New South Wales, Sydney NSW 2052, Australia. E-mail: j.kidston@unsw.edu.au

Abstract

A stirred barotropic model on a sphere is used to investigate the relationship between the speed and the latitude of an eddy-driven jet. When the wind speed is increased in the model, the jet shifts poleward, despite the fact that the stirring of vorticity remains statistically constant. The cause is found to be increasing meridional shear that results from increasing the wind speed in a meridionally confined region and reduces the absolute vorticity gradient on the flanks of the jet. This has two related consequences. The first is that wave propagation is discouraged, as a turning latitude is created where the absolute vorticity gradient tends to zero. On the sphere, this occurs first at high latitudes, thereby shifting wave dissipation toward the equator. The reduced high-latitude dissipation causes a poleward shift of the jet. The second consequence occurs when the vorticity gradient actually becomes negative, in which case the waves may overreflect where an instability is present, providing a high-latitude source of pseudomomentum. This may further encourage the jet to shift poleward.

The relevance of the barotropic dynamics to more realistic atmospheres is unclear, but the intermodel variability of the poleward shift of the jet in response to increasing CO2 across a suite of state-of-the-art GCMs is consistent with the barotropic dynamics, suggesting that further investigation is warranted.

Corresponding author address: J. Kidston, Climate Change Research Centre, Level 4 Matthew’s Building, University of New South Wales, Sydney NSW 2052, Australia. E-mail: j.kidston@unsw.edu.au
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