Editorial Type:
Article
Article Type:
Research Article

The Role of Nonquasigeostrophic Forcing in Southern Hemisphere Blocking Onsets

Li Dong Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York

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Stephen J. Colucci Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York

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Print Publication:
01 Apr 2015
DOI:
https://doi.org/10.1175/MWR-D-14-00356.1
Page(s):
1455–1471
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Abstract

A generalized frictionless, adiabatic geostrophic zonal wind tendency equation is derived to diagnose the nonquasigeostrophic forcings to blocking onset in the Southern Hemisphere through case study and composite analysis. In general, the quasigeostrophic model is capable of representing the key physical processes associated with blocking onset in the troposphere reasonably well in most blocking cases. The consideration of nonquasigeostrophic forcings moderately improves the quasigeostrophic representation in a majority of the blocking events selected for this study, but not all events. This suggests that the nonquasigeostrophic terms could be important in a specific blocking event but not in a composite meaning. Furthermore, the nonquasigeostrophic forcing of geostrophic advection of ageostrophic relative vorticity term, , is extensively examined in this study. This forcing is found to be the leading nonquasigeostrophic forcing term among all nonquasigeostrophic forcings. In a composite sense, the forcing appears to have an alternative contribution that is dependent upon the curvature of the geostrophic flow within the blocking structure. In general, the southwesterly flow is likely associated with the -favoring effect to blocking onset whereas northwesterly flow is associated with the -opposing effect. Therefore, it is important to use the geostrophic flow pattern prior to blocking onset to foresee this ageostrophic-related nonquasigeostrophic forcing to blocking onset. Finally, a pronounced overestimation of geostrophic zonal wind tendency by the quasigeostrophic model is commonly found for selected blocking events within the stratosphere, in comparison to the nonquasigeostrophic model. This overestimation is essentially caused by geostrophic wind approximation.

Current affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, and Department of Geology and Geography, Auburn University, Auburn, Alabama.

Corresponding author address: Li Dong, School of Forestry and Wildlife Sciences, Auburn University, 602 Duncan Dr., Rm. 4229, Auburn, AL 36849. E-mail: ldong@auburn.edu

Abstract

A generalized frictionless, adiabatic geostrophic zonal wind tendency equation is derived to diagnose the nonquasigeostrophic forcings to blocking onset in the Southern Hemisphere through case study and composite analysis. In general, the quasigeostrophic model is capable of representing the key physical processes associated with blocking onset in the troposphere reasonably well in most blocking cases. The consideration of nonquasigeostrophic forcings moderately improves the quasigeostrophic representation in a majority of the blocking events selected for this study, but not all events. This suggests that the nonquasigeostrophic terms could be important in a specific blocking event but not in a composite meaning. Furthermore, the nonquasigeostrophic forcing of geostrophic advection of ageostrophic relative vorticity term, , is extensively examined in this study. This forcing is found to be the leading nonquasigeostrophic forcing term among all nonquasigeostrophic forcings. In a composite sense, the forcing appears to have an alternative contribution that is dependent upon the curvature of the geostrophic flow within the blocking structure. In general, the southwesterly flow is likely associated with the -favoring effect to blocking onset whereas northwesterly flow is associated with the -opposing effect. Therefore, it is important to use the geostrophic flow pattern prior to blocking onset to foresee this ageostrophic-related nonquasigeostrophic forcing to blocking onset. Finally, a pronounced overestimation of geostrophic zonal wind tendency by the quasigeostrophic model is commonly found for selected blocking events within the stratosphere, in comparison to the nonquasigeostrophic model. This overestimation is essentially caused by geostrophic wind approximation.

Current affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, and Department of Geology and Geography, Auburn University, Auburn, Alabama.

Corresponding author address: Li Dong, School of Forestry and Wildlife Sciences, Auburn University, 602 Duncan Dr., Rm. 4229, Auburn, AL 36849. E-mail: ldong@auburn.edu
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  • Alberta, T. L., S. J. Colucci, and J. C. Davenport, 1991: Rapid 500-mb cyclogenesis and anticyclogenesis. Mon. Wea. Rev., 119, 1186–1204, doi:10.1175/1520-0493(1991)119<1186:RMCAA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Bengtsson, L., 1981: Numerical prediction of atmospheric blocking—A case study. Tellus, 33A, 19–42, doi:10.1111/j.2153-3490.1981.tb01728.x.

    • Search Google Scholar
    • Export Citation

  • Berrisford, P., B. J. Hoskins, and E. Tyrlis, 2007: Blocking and Rossby wave breaking on the dynamical tropopause in the Southern Hemisphere. J. Atmos. Sci., 64, 2881–2898, doi:10.1175/JAS3984.1.

    • Search Google Scholar
    • Export Citation

  • Bluestein, H. B., 1992: Synoptic-Dynamic Meteorology in Midlatitudes. Vol. 2. Oxford University Press, 594 pp.

  • Boville, B. A., 1987: The validity of the geostrophic approximation in the winter stratosphere and troposphere. J. Atmos. Sci., 44, 443–457, doi:10.1175/1520-0469(1987)044<0443:TVOTGA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Dong, L., and S. J. Colucci, 2005: The role of deformation and potential vorticity in Southern Hemisphere blocking onsets. J. Atmos. Sci., 62, 4043–4056, doi:10.1175/JAS3576.1.

    • Search Google Scholar
    • Export Citation

  • Gong, T., S. B. Feldstein, and D. Luo, 2010: The impact of ENSO on wave breaking and southern annular mode events. J. Atmos. Sci., 67, 2854–2870, doi:10.1175/2010JAS3311.1.

    • Search Google Scholar
    • Export Citation

  • Holton, J. R., 2004: An Introduction to Dynamic Meteorology. 4th ed. Academic Press, 535 pp.

  • Illari, L., 1984: A diagnostic study of the potential vorticity in a warm blocking anticylone. J. Atmos. Sci., 41, 3518–3526, doi:10.1175/1520-0469(1984)041<3518:ADSOTP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77, 437–471, doi:10.1175/1520-0477(1996)077<0437:TNYRP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Krishnamurti, T. N., 1968: A diagnostic balance model for studies of weather systems of low and high latitudes, Rossby number less than 1. Mon. Wea. Rev., 96, 197–207, doi:10.1175/1520-0493(1968)096<0197:ADBMFS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Lupo, A. R., 2002: Ageostrophic forcing in a height tendency equation. Mon. Wea. Rev., 130, 115–126, doi:10.1175/1520-0493(2002)130<0115:AFIAHT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Lupo, A. R., and P. J. Smith, 1995: Planetary and synoptic-scale interactions during the life cycle of a mid-latitude blocking anticyclone over the North Atlantic. Tellus, 47A, 575–596, doi:10.1034/j.1600-0870.1995.00106.x.

    • Search Google Scholar
    • Export Citation

  • Mullen, S. L., 1987: Transient eddy forcing of blocking flows. J. Atmos. Sci., 44, 3–22, doi:10.1175/1520-0469(1987)044<0003:TEFOBF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Peters, D., and D. W. Waugh, 2003: Robssy wave breaking in the Southern Hemisphere wintertime upper troposphere. Mon. Wea. Rev., 131, 2623–2634, doi:10.1175/1520-0493(2003)131<2623:RWBITS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Raisanen, J., 1997: Height tendency diagnostics using a generalized omega equation, the vorticity equation, and a nonlinear balance equation. Mon. Wea. Rev., 125, 1577–1597, doi:10.1175/1520-0493(1997)125<1577:HTDUAG>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Randel, W. J., 1987: The evaluation of winds from geopotential height data in the stratosphere. J. Atmos. Sci., 44, 3097–3120, doi:10.1175/1520-0469(1987)044<3097:TEOWFG>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Shutts, G. J., 1983: The propagation of eddies in diffluent jetstreams: Eddy vorticity forcing of “blocking” flow fields. Quart. J. Roy. Meteor. Soc., 109, 737–761, doi:10.1002/qj.49710946204.

    • Search Google Scholar
    • Export Citation

  • Tibaldi, S., and F. Molteni, 1990: On the operational predictability of blocking. Tellus, 42A, 343–365, doi:10.1034/j.1600-0870.1990.t01-2-00003.x.

    • Search Google Scholar
    • Export Citation

  • Tsou, C.-H., and P. J. Smith, 1990: The role of synoptic/planetary scale interactions during the development of a blocking anticyclone. Tellus, 42A, 174–193, doi:10.1034/j.1600-0870.1990.00015.x.

    • Search Google Scholar
    • Export Citation

  • Watson, J. S., and S. J. Colucci, 2002: Evaluation of ensemble predictions of blocking in the NCEP global spectral model. Mon. Wea. Rev., 130, 3008–3021, doi:10.1175/1520-0493(2002)130<3008:EOEPOB>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
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