The Modeled Response of the Mean Winter Circulation to Zonally Averaged SST Trends

Gudrun Magnusdottir Department of Earth System Science, University of California, Irvine, Irvine, California

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Abstract

The response of the atmospheric winter circulation in both hemispheres to changes in the meridional gradient of sea surface temperature (SST) is examined in an atmospheric general circulation model. Climatological SSTs are employed for the control run. The other runs differ in that a zonally symmetric component is added to or subtracted from the climatological SST field. The meridional structure of the variation in SST gradient is based on the observed change in zonally averaged SST over the last century. The SST trend has maxima of about 1 K at high latitudes of both hemispheres. Elsewhere, the increase in SST over the last century is fairly uniform at about 0.5 K.

In both hemispheres the response to decreased SST gradients is decreased baroclinity in the lower troposphere and increased baroclinity in the upper troposphere, with the reverse response when the SST gradient is increased. Because the cases with decreased SST gradients correspond to warmer SSTs everywhere, they are accompanied by an increase in moisture and a general expansion of the troposphere. The warming cases in the Northern Hemisphere (NH) winter are marked by greatly increased tropical convection, a stronger subtropical jet that is shifted upward and equatorward, and a robust stationary-wave response. Many aspects of the response are remarkably consistent among the different warming experiments, both in pattern and amplitude. The storm-track response is weaker but still consistent among the different warming experiments. Despite general decrease in storm-track activity, there is a tendency for the upper-level NH storm tracks to strengthen at their downstream end and to weaken at their upstream and northward end. When the zonally symmetric SST anomaly field is subtracted from the climatological SST (resulting in lower SST with increased latitudinal gradient), the response is different in many fields and is considerably weaker.

In the winter Southern Hemisphere the change in baroclinity of the low-level flow plays a greater role in the response than in the winter NH. The response in the storm track is zonal with a decrease in midlatitude storm-track activity in the warming cases and an increase in the case that has an increased SST gradient (and cooler SST). There is close correspondence between the pattern of response in all the experiments, irrespective of the sign of the SST anomaly field.

Corresponding author address: Dr. Gudrun Magnusdottir, Department of Earth System Science, University of California, Irvine, Irvine, CA 92697-3100. Email: gudrun@uci.edu

Abstract

The response of the atmospheric winter circulation in both hemispheres to changes in the meridional gradient of sea surface temperature (SST) is examined in an atmospheric general circulation model. Climatological SSTs are employed for the control run. The other runs differ in that a zonally symmetric component is added to or subtracted from the climatological SST field. The meridional structure of the variation in SST gradient is based on the observed change in zonally averaged SST over the last century. The SST trend has maxima of about 1 K at high latitudes of both hemispheres. Elsewhere, the increase in SST over the last century is fairly uniform at about 0.5 K.

In both hemispheres the response to decreased SST gradients is decreased baroclinity in the lower troposphere and increased baroclinity in the upper troposphere, with the reverse response when the SST gradient is increased. Because the cases with decreased SST gradients correspond to warmer SSTs everywhere, they are accompanied by an increase in moisture and a general expansion of the troposphere. The warming cases in the Northern Hemisphere (NH) winter are marked by greatly increased tropical convection, a stronger subtropical jet that is shifted upward and equatorward, and a robust stationary-wave response. Many aspects of the response are remarkably consistent among the different warming experiments, both in pattern and amplitude. The storm-track response is weaker but still consistent among the different warming experiments. Despite general decrease in storm-track activity, there is a tendency for the upper-level NH storm tracks to strengthen at their downstream end and to weaken at their upstream and northward end. When the zonally symmetric SST anomaly field is subtracted from the climatological SST (resulting in lower SST with increased latitudinal gradient), the response is different in many fields and is considerably weaker.

In the winter Southern Hemisphere the change in baroclinity of the low-level flow plays a greater role in the response than in the winter NH. The response in the storm track is zonal with a decrease in midlatitude storm-track activity in the warming cases and an increase in the case that has an increased SST gradient (and cooler SST). There is close correspondence between the pattern of response in all the experiments, irrespective of the sign of the SST anomaly field.

Corresponding author address: Dr. Gudrun Magnusdottir, Department of Earth System Science, University of California, Irvine, Irvine, CA 92697-3100. Email: gudrun@uci.edu

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  • Carnell, R. E., C. A. Senior, and J. F. B. Mitchell, 1996: An assessment of measures of storminess: simulated changed in northern hemisphere winter due to increasing CO2. Climate Dyn, 12 , 467476.

    • Search Google Scholar
    • Export Citation
  • Edmon, H. J., B. J. Hoskins, and M. E. McIntyre, 1980: Eliassen–Palm cross sections for the troposphere. J. Atmos. Sci, 37 , 26002616.

    • Search Google Scholar
    • Export Citation
  • Hack, J. J., J. T. Kiehl, and J. W. Hurrell, 1998: The hydrologic and thermodynamic characteristics of the NCAR CCM3. J. Climate, 11 , 11791206.

    • Search Google Scholar
    • Export Citation
  • Hall, N. M. J., B. J. Hoskins, P. J. Valdes, and C. A. Senior, 1994: Storm tracks in a high-resolution GCM with doubled carbon dioxide Quart. J. Roy. Meteor. Soc, 120 , 12091230.

    • Search Google Scholar
    • Export Citation
  • Held, I. M., and P. J. Phillips, 1993: Sensitivity of the eddy momentum flux to meridional resolution in atmospheric GCMs. J. Climate, 6 , 499507.

    • Search Google Scholar
    • Export Citation
  • Hoskins, B. J., I. N. James, and G. H. White, 1983: The shape, propagation and mean flow interactions of large scale weather systems. J. Atmos. Sci, 40 , 15951612.

    • Search Google Scholar
    • Export Citation
  • Hurrell, J. W., J. J. Hack, B. A. Boville, D. L. Williamson, and J. T. Kiehl, 1998: The dynamical simulation of the NCAR Community Climate Model Version 3 (CCM3). J. Climate, 11 , 12071236.

    • Search Google Scholar
    • Export Citation
  • Kageyama, M., P. J. Valdes, G. Ramstein, C. Hewitt, and U. Wyputta, 1999: Northern Hemisphere storm tracks in present day and last glacial maximum climate simulations: A comparison of the European PMIP models. J. Climate, 12 , 742760.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E., and and Coauthors, 1996: The NCAR/NCEP 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc, 77 , 437471.

  • Kiehl, J. T., J. J. Hack, G. B. Bonan, B. A. Boville, D. L. Williamson, and P. J. Rasch, 1998: The National Center for Atmospheric Research Community Climate Model: CCM3. J. Climate, 11 , 11311149.

    • Search Google Scholar
    • Export Citation
  • Magnusdottir, G., and R. Saravanan, 1999: The response of atmospheric heat transport to zonally averaged SST trends. Tellus, 51A , 815832.

    • Search Google Scholar
    • Export Citation
  • Pavan, V., 1996: Sensitivity of a multi-layer quasi-geostrophic β-channel to the vertical structure of the equilibrium meridional temperature gradient. Quart. J. Roy. Meteor. Soc, 122 , 5572.

    • Search Google Scholar
    • Export Citation
  • Pavan, V., N. Hall, P. Valdes, and M. Blackburn, 1999: The importance of moisture distribution for the growth and energetics of mid-latitude systems. Ann. Geophys, 17 , 242256.

    • Search Google Scholar
    • Export Citation
  • Peixoto, J. P., and A. H. Oort, 1992: Physics of Climate. American Institute of Physics, 550 pp.

  • Rayner, N. A., C. K. Folland, D. E. Parker, and E. B. Horton, 1995: A new global sea-ice and sea surface temperature (GISST) data set for 1903–1994 for forcing climate models. Hadley Centre Internal Note No. 69, 9 pp. [Available from the Hadley Centre, Met Office, London Road, Bracknell, Berkshire RG12 2SZ United Kingdom.].

    • Search Google Scholar
    • Export Citation
  • Rind, D., 1998: Latitudinal temperature gradients and climate change. J. Geophys. Res, 103 , 59435971.

  • Robinson, W. A., 2000: Review of the workshop on extratropical SST anomalies. Bull. Amer. Meteor. Soc, 81 , 567577.

  • Schubert, M., J. Perlwitz, R. Blender, K. Fraedrich, and F. Lunkeit, 1998: North Atlantic cyclones in CO2-induced warm climate simulations: Frequency, intensity, and tracks. Climate Dyn, 14 , 827837.

    • Search Google Scholar
    • Export Citation
  • Stephenson, D. B., and I. M. Held, 1993: GCM response of northern winter stationary waves and storm tracks to increasing amounts of carbon dioxide. J. Climate, 6 , 18591870.

    • Search Google Scholar
    • Export Citation
  • Thuburn, J., and G. C. Craig, 1997: GCM tests of theories for the height of the tropopause. J. Atmos. Sci, 54 , 869882.

  • Timbal, B., J-F. Mahfouf, J-F. Royer, and D. Cariolle, 1995: Sensitivity to prescribed changes in sea surface temperature and sea ice in doubled carbon dioxide experiments. Climate Dyn, 12 , 120.

    • Search Google Scholar
    • Export Citation
  • Trenberth, K. E., 1991: Storm tracks in the Southern Hemisphere. J. Atmos. Sci, 48 , 21592178.

  • Ulbrich, U., and M. Cristoph, 1999: A shift of the NAO and increasing storm activity over Europe due to anthropogenic greenhouse gas forcing. Climate Dyn, 15 , 551559.

    • Search Google Scholar
    • Export Citation
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