Editorial Type:
Article
Article Type:
Research Article

Eddy–Zonal Flow Feedback in the Southern Hemisphere Winter and Summer

Xiaosong Yang ITPA/Marine Sciences Research Center, Stony Brook University, Stony Brook, New York

Search for other papers by Xiaosong Yang in
Current site
Google Scholar
PubMed Close
and
Edmund K. M. Chang ITPA/Marine Sciences Research Center, Stony Brook University, Stony Brook, New York

Search for other papers by Edmund K. M. Chang in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Sep 2007
DOI:
https://doi.org/10.1175/JAS4005.1
Page(s):
3091–3112
Restricted access

Abstract

The eddy–zonal flow feedback in the Southern Hemisphere (SH) winter and summer is investigated in this study. The persistence time scale of the leading principal components (PCs) of the zonal-mean zonal flow shows substantial seasonal variation. In the SH summer, the persistence time scale of PC1 is significantly longer than that of PC2, while the persistence time scales of the two PCs are quite similar in the SH winter. A storm-track modeling approach is applied to demonstrate that seasonal variations of eddy–zonal flow feedback for PC1 and PC2 account for the seasonal variations of the persistence time scale. The eddy feedback time scale estimated from a storm-track model simulation and a wave-response model diagnostic shows that PC1 in June–August (JJA) and December–February (DJF), and PC2 in JJA, have significant positive eddy–mean flow feedback, while PC2 in DJF has no positive feedback. The consistency between the persistence and eddy feedback time scales for each PC suggests that the positive feedback increases the persistence of the corresponding PC, with stronger (weaker) positive feedback giving rise to a longer (shorter) persistence time scale.

Eliassen–Palm flux diagnostics have been performed to demonstrate the dynamics governing the positive feedback between eddies and anomalous zonal flow. The mechanism of the positive feedback, for PC1 in JJA and DJF and PC2 in JJA, is as follows: an enhanced baroclinic wave source (heat fluxes) at a low level in the region of positive wind anomalies propagates upward and then equatorward from the wave source, thus giving momentum fluxes that reinforce the wind anomalies. The difference of PC2 between DJF and JJA is because of the zonal asymmetry of the climatological flow in JJA. For PC2 in DJF, wind anomalies reinforce the climatological jet, thus increasing the barotropic shear of the jet flow. The “barotropic governor” plays an important role in suppressing eddy generations for PC2 in DJF and thus inhibiting the positive eddy–zonal flow feedback.

* Current affiliation: Center for Ocean–Land–Atmosphere Studies, Calverton, Maryland

Corresponding author address: Dr. Edmund K. M. Chang, Institute for Terrestrial and Planetary Atmospheres, Marine Sciences Research Center, Stony Brook University, Stony Brook, NY 11794-5000. Email: kmchang@notes.cc.sunysb.edu

Abstract

The eddy–zonal flow feedback in the Southern Hemisphere (SH) winter and summer is investigated in this study. The persistence time scale of the leading principal components (PCs) of the zonal-mean zonal flow shows substantial seasonal variation. In the SH summer, the persistence time scale of PC1 is significantly longer than that of PC2, while the persistence time scales of the two PCs are quite similar in the SH winter. A storm-track modeling approach is applied to demonstrate that seasonal variations of eddy–zonal flow feedback for PC1 and PC2 account for the seasonal variations of the persistence time scale. The eddy feedback time scale estimated from a storm-track model simulation and a wave-response model diagnostic shows that PC1 in June–August (JJA) and December–February (DJF), and PC2 in JJA, have significant positive eddy–mean flow feedback, while PC2 in DJF has no positive feedback. The consistency between the persistence and eddy feedback time scales for each PC suggests that the positive feedback increases the persistence of the corresponding PC, with stronger (weaker) positive feedback giving rise to a longer (shorter) persistence time scale.

Eliassen–Palm flux diagnostics have been performed to demonstrate the dynamics governing the positive feedback between eddies and anomalous zonal flow. The mechanism of the positive feedback, for PC1 in JJA and DJF and PC2 in JJA, is as follows: an enhanced baroclinic wave source (heat fluxes) at a low level in the region of positive wind anomalies propagates upward and then equatorward from the wave source, thus giving momentum fluxes that reinforce the wind anomalies. The difference of PC2 between DJF and JJA is because of the zonal asymmetry of the climatological flow in JJA. For PC2 in DJF, wind anomalies reinforce the climatological jet, thus increasing the barotropic shear of the jet flow. The “barotropic governor” plays an important role in suppressing eddy generations for PC2 in DJF and thus inhibiting the positive eddy–zonal flow feedback.

* Current affiliation: Center for Ocean–Land–Atmosphere Studies, Calverton, Maryland

Corresponding author address: Dr. Edmund K. M. Chang, Institute for Terrestrial and Planetary Atmospheres, Marine Sciences Research Center, Stony Brook University, Stony Brook, NY 11794-5000. Email: kmchang@notes.cc.sunysb.edu

Save
Cover Journal of the Atmospheric Sciences
Journal of the Atmospheric Sciences

  • Anderson, D., K. I. Hodges, and B. J. Hoskins, 2003: Sensitivity of feature-based analysis methods of storm tracks to the form of background field removal. Mon. Wea. Rev., 131 , 565–573.

    • Search Google Scholar
    • Export Citation

  • Bals-Elsholz, T. M., E. H. Atallah, L. F. Bosart, T. A. Wasula, M. J. Cempa, and A. R. Lupo, 2001: The wintertime Southern Hemisphere split jet: Structure, variability, and evolution. J. Climate, 14 , 4191–4215.

    • Search Google Scholar
    • Export Citation

  • Branstator, G., 1995: Organization of storm track anomalies by recurring low-frequency circulation anomalies. J. Atmos. Sci., 52 , 207–226.

    • Search Google Scholar
    • Export Citation

  • Chang, E. K. M., 1993: Downstream development of baroclinic waves as inferred from regression analysis. J. Atmos. Sci., 50 , 2038–2053.

    • Search Google Scholar
    • Export Citation

  • Chang, E. K. M., S. Lee, and K. L. Swanson, 2002: Storm track dynamics. J. Climate, 15 , 2163–2183.

  • Codron, F., 2005: Relation between annular modes and the mean state: Southern Hemisphere summer. J. Climate, 18 , 320–330.

  • Edmon, H. J., B. J. Hoskins, and M. E. McIntyre, 1980: Eliassen–Palm cross sections for the troposphere. J. Atmos. Sci., 37 , 2600–2616. Corrigendum, 38, 1115.

    • Search Google Scholar
    • Export Citation

  • Feldstein, S. B., 2000: Is interannual zonal mean flow variability simply climate noise? J. Climate, 13 , 2356–2362.

  • Feldstein, S. B., and S. Lee, 1996: Mechanisms of zonal index variability in an aquaplanet GCM. J. Atmos. Sci., 53 , 3541–3555.

  • Feldstein, S. B., and S. Lee, 1998: Is the atmospheric zonal index driven by an eddy feedback? J. Atmos. Sci., 55 , 3077–3086.

  • Gong, D., and S. Wang, 1999: Definition of Antarctic Oscillation index. Geophys. Res. Lett., 26 , 459–462.

  • Hartmann, D. L., and F. Lo, 1998: Wave-driven zonal flow vacillation in the Southern Hemisphere. J. Atmos. Sci., 55 , 1303–1315.

  • Held, I. M., and M. J. Suarez, 1994: A proposal for the intercomparison of the dynamical cores of atmospheric circulation models. Bull. Amer. Meteor. Soc., 75 , 1825–1830.

    • Search Google Scholar
    • Export Citation

  • Hurrell, J. W., H. Van Loon, and D. J. Shea, 1998: The mean state of the troposphere. Meteorology of the Southern Hemisphere, Meteor. Monogr., No. 49, Amer. Meteor. Soc., 1–46.

  • James, I. N., 1987: Suppression of baroclinic instability in horizontal sheared flows. J. Atmos. Sci., 44 , 3710–3720.

  • Karoly, D. J., 1990: The role of transient eddies in low-frequency zonal variations of the Southern Hemisphere circulation. Tellus, 42A , 41–50.

    • Search Google Scholar
    • Export Citation

  • Kidson, J. W., 1988: Indices of the Southern Hemisphere zonal wind. J. Climate, 1 , 183–194.

  • Kidson, J. W., and M. R. Sinclair, 1995: The influence of persistent anomalies on Southern Hemisphere storm tracks. J. Climate, 8 , 1938–1950.

    • Search Google Scholar
    • Export Citation

  • Lee, S., 1997: Maintenance of multiple jets in a baroclinic flow. J. Atmos. Sci., 54 , 1726–1738.

  • Lee, S., and S. B. Feldstein, 1996: Mechanism of zonal index evolution in a two-layer model. J. Atmos. Sci., 53 , 2232–2246.

  • Lorenz, D. J., and D. L. Hartmann, 2001: Eddy–zonal flow feedback in the Southern Hemisphere. J. Atmos. Sci., 58 , 3312–3327.

  • Lorenz, D. J., and D. L. Hartmann, 2003: Eddy–zonal flow feedback in the Northern Hemisphere winter. J. Climate, 16 , 1212–1227.

  • Nakamura, H., and A. Shimpo, 2004: Seasonal variations in the Southern Hemisphere storm tracks and jet streams as revealed in a reanalysis dataset. J. Climate, 17 , 1828–1844.

    • Search Google Scholar
    • Export Citation

  • Ogi, M., K. Yamazaki, and Y. Tachibana, 2004: The summertime annular mode in the Northern Hemisphere and its linkage to the winter mode. J. Geophys. Res., 109 .D20114, doi:10.1029/2004JD004514.

    • Search Google Scholar
    • Export Citation

  • Pan, L-L., and F-F. Jin, 2005: Seasonality of synoptic eddy feedback and the AO/NAO. Geophys. Res. Lett., 32 .L21708, doi:10.1029/2005GL024133.

    • Search Google Scholar
    • Export Citation

  • Portis, D. H., J. E. Walsh, M. E. Hamly, and P. J. Lamb, 2001: Seasonality of the North Atlantic Oscillation. J. Climate, 14 , 2069–2078.

    • Search Google Scholar
    • Export Citation

  • Robinson, W. A., 1996: Does eddy feedback sustain variability in the zonal index? J. Atmos. Sci., 53 , 3556–3569.

  • Taljaard, J. J., 1972: Synoptic meteorology of the Southern Hemisphere. Meteorology of the Southern Hemisphere, Meteor. Monogr., No. 35, Amer. Meteor. Soc., 139–211.

  • Thompson, D. W. J., and J. M. Wallace, 1998: The Arctic Oscillation signature in the wintertime geopotential height and temperature fields. Geophys. Res. Lett., 25 , 1297–1300.

    • Search Google Scholar
    • Export Citation

  • Thompson, D. W. J., and J. M. Wallace, 2000: Annular modes in the extratropical circulation. Part I: Month-to-month variability. J. Climate, 13 , 1000–1016.

    • Search Google Scholar
    • Export Citation

  • Trenberth, K. E., 1991: Storm tracks in the Southern Hemisphere. J. Atmos. Sci., 48 , 2159–2178.

  • Watterson, I. G., 2002: Wave–mean flow feedback and the persistence of simulated zonal flow vacillation. J. Atmos. Sci., 59 , 1274–1288.

    • Search Google Scholar
    • Export Citation

  • Watterson, I. G., 2007: Southern “annular modes” simulated by a climate model—Patterns, mechanisms, and uses. J. Atmos. Sci., 64 , 3113–3131.

    • Search Google Scholar
    • Export Citation

  • Yang, X., and E. K. M. Chang, 2006: Variability of the Southern Hemisphere winter split flow—A case of two-way reinforcement between mean flow and eddy anomalies. J. Atmos. Sci., 63 , 634–650.

    • Search Google Scholar
    • Export Citation

  • Zhang, Y., and I. M. Held, 1999: A linear stochastic model of a GCM’s midlatitude storm tracks. J. Atmos. Sci., 56 , 3416–3435.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 150 41 2
PDF Downloads 82 31 3