Simulations of the Atmospheric Response to South Atlantic Sea Surface Temperature Anomalies

Andrew W. Robertson International Research Institute for Climate Prediction, Palisades, New York

Search for other papers by Andrew W. Robertson in
Current site
Google Scholar
PubMed
Close
,
John D. Farrara Department of Atmospheric Sciences, University of California, Los Angeles, Los Angeles, California

Search for other papers by John D. Farrara in
Current site
Google Scholar
PubMed
Close
, and
Carlos R. Mechoso Department of Atmospheric Sciences, University of California, Los Angeles, Los Angeles, California

Search for other papers by Carlos R. Mechoso in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

The sensitivity of the atmospheric circulation to sea surface temperature (SST) anomalies in the tropical and subtropical South Atlantic Ocean is studied by means of simulations with an atmospheric general circulation model (GCM). Two types of prescribed SST anomalies are used, motivated by previous analyses of data. The first occurs during austral summers in association with a strengthening of the South Atlantic convergence zone (SACZ) and consists of cold SST anomalies over the subtropical South Atlantic. The second is the leading seasonally varying empirical orthogonal function of SST, consisting of warm basin-scale anomalies with maximum amplitude in the subtropics during January–March and at the equator in June. An ensemble of about 10 seasonal simulations is made using each type of anomaly, focusing on the January–March period in the first case and the January–June seasonal evolution in the second.

During January–March both experiments yield a statistically significant baroclinic response over the subtropical Atlantic with dipolar SACZ-like anomalies. Some evidence of positive feedback is found. The response is shown to be fairly similar in pattern as well as amplitude to the linear regression of observed interannual low-level wind anomalies with subtropical SST anomalies. However, in the first experiment with cold SST anomalies, the simulated response contrasts with the leading interannual mode of observed SACZ variability.

Warm basin-scale anomalies are found to have their largest impact during boreal summer, with a strong statistically significant equatorial baroclinic response and positive rainfall anomalies over the equatorial ocean. The latter do not extend appreciably into the adjacent continents, although there are significant positive rainfall anomalies over the Sahel in April–June and negative anomalies over the western Indian Ocean. In the upper troposphere, a statistically significant wave train extends southwestward to southern South America and northeastward to Europe in April–June, while there is some linkage between the tropically and subtropically forced responses during January–March.

Corresponding author address: Dr. Andrew W. Robertson, International Research Institute for Climate Prediction, P.O. Box 1000, Palisades, NY 10964. Email: awr@iri.columbia.edu

Abstract

The sensitivity of the atmospheric circulation to sea surface temperature (SST) anomalies in the tropical and subtropical South Atlantic Ocean is studied by means of simulations with an atmospheric general circulation model (GCM). Two types of prescribed SST anomalies are used, motivated by previous analyses of data. The first occurs during austral summers in association with a strengthening of the South Atlantic convergence zone (SACZ) and consists of cold SST anomalies over the subtropical South Atlantic. The second is the leading seasonally varying empirical orthogonal function of SST, consisting of warm basin-scale anomalies with maximum amplitude in the subtropics during January–March and at the equator in June. An ensemble of about 10 seasonal simulations is made using each type of anomaly, focusing on the January–March period in the first case and the January–June seasonal evolution in the second.

During January–March both experiments yield a statistically significant baroclinic response over the subtropical Atlantic with dipolar SACZ-like anomalies. Some evidence of positive feedback is found. The response is shown to be fairly similar in pattern as well as amplitude to the linear regression of observed interannual low-level wind anomalies with subtropical SST anomalies. However, in the first experiment with cold SST anomalies, the simulated response contrasts with the leading interannual mode of observed SACZ variability.

Warm basin-scale anomalies are found to have their largest impact during boreal summer, with a strong statistically significant equatorial baroclinic response and positive rainfall anomalies over the equatorial ocean. The latter do not extend appreciably into the adjacent continents, although there are significant positive rainfall anomalies over the Sahel in April–June and negative anomalies over the western Indian Ocean. In the upper troposphere, a statistically significant wave train extends southwestward to southern South America and northeastward to Europe in April–June, while there is some linkage between the tropically and subtropically forced responses during January–March.

Corresponding author address: Dr. Andrew W. Robertson, International Research Institute for Climate Prediction, P.O. Box 1000, Palisades, NY 10964. Email: awr@iri.columbia.edu

Save
  • Arakawa, A., and W. H. Schubert, 1974: Interaction of a cumulus ensemble with the large-scale environment. Part I. J. Atmos. Sci., 31 , 674701.

    • Search Google Scholar
    • Export Citation
  • Barreiro, M., P. Chang, and R. Saravanan, 2002: Variability of the South Atlantic convergence zone simulated by an atmospheric general circulation model. J. Climate, 15 , 745763.

    • Search Google Scholar
    • Export Citation
  • Barros, V., M. Gonzalez, B. Liebmann, and I. Camilloni, 2000: Influence of the South Atlantic convergence zone and South Atlantic sea surface temperature on interannual summer rainfall variability in southeastern South America. Theor. Appl. Climatol., 67 , 123133.

    • Search Google Scholar
    • Export Citation
  • Barsugli, J. J., and D. S. Battisti, 1998: The basic effects of atmosphere–ocean thermal coupling on midlatitude variability. J. Atmos. Sci., 55 , 477493.

    • Search Google Scholar
    • Export Citation
  • Cazes-Boezio, G., A. W. Robertson, and C. R. Mechoso, 2003: Seasonal dependence of ENSO teleconnections over South America and relationships with precipitation in Uruguay. J. Climate, 16 , 11591176.

    • Search Google Scholar
    • Export Citation
  • Chang, P., L. Ji, and H. Li, 1997: A decadal climate variation in the tropical Atlantic ocean from thermodynamic air–sea interactions. Nature, 385 , 516518.

    • Search Google Scholar
    • Export Citation
  • Chang, P., R. Saravanan, L. Ji, and G. C. Hegerl, 2000: The effect of local sea surface temperatures on atmospheric circulation over the tropical Atlantic sector. J. Climate, 13 , 21952216.

    • Search Google Scholar
    • Export Citation
  • Davis, R. E., 1976: Predictability of sea surface temperature and sea level pressure anomalies over the North Pacific Ocean. J. Phys. Oceanogr., 6 , 249266.

    • Search Google Scholar
    • Export Citation
  • Diaz, A. F., C. D. Studzinski, and C. R. Mechoso, 1998: Relationships between precipitation anomalies in Uruguay and Southern Brazil and sea surface temperatures in the Pacific and Atlantic Oceans. J. Climate, 11 , 251271.

    • Search Google Scholar
    • Export Citation
  • Dommenget, D., and M. Latif, 2000: Interannual to decadal variability in the tropical Atlantic. J. Climate, 13 , 777792.

  • Enfield, D. B., and D. A. Mayer, 1997: Tropical Atlantic sea surface temperature variability and its relation to El Niño–Southern Oscillation. J. Geophys. Res., 102 , 929945.

    • Search Google Scholar
    • Export Citation
  • Farrara, J. D., C. R. Mechoso, and A. W. Robertson, 2000: Ensembles of AGCM two-tier predictions and simulations of the circulation anomalies during winter 1997–98. Mon. Wea. Rev., 128 , 35893604.

    • Search Google Scholar
    • Export Citation
  • Gandu, A. W., and P. L. Silva Dias, 1998: Impact of tropical heat sources on the South American tropospheric upper circulation and subsidence. J. Geophys. Res., 103 , 60016015.

    • Search Google Scholar
    • Export Citation
  • Harshvardhan, R. Davies, D. A. Randall, and T. G. Corsetti, 1987: A fast radiation parameterization for atmospheric circulation models. J. Geophys. Res., 92 , 10091016.

    • Search Google Scholar
    • Export Citation
  • Harshvardhan, R. Davies, D. A. Randall, T. G. Corsetti, and D. A. Dazlich, 1989: Earth radiation budget and cloudiness simulations with a general circulation model. J. Atmos. Sci., 46 , 19221942.

    • Search Google Scholar
    • Export Citation
  • Horel, J. D., A. N. Hahnmann, and J. E. Geisler, 1989: An investigation of the annual cycle of the convective activity over the tropical Americas. J. Climate, 2 , 13881403.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E., K. C. Mo, and J. Paegle, 1986: Large-amplitude, short-scale stationary Rossby waves in the Southern Hemisphere: Observations and mechanistic experiments to determine their origin. J. Atmos. Sci., 43 , 252275.

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

  • Kodama, Y-M., 1992: Large-scale common features of subtropical precipitation zones (the Baiu frontal zone, the SPCZ, the SACZ). Part I: Characteristics of subtropical frontal zones. J. Meteor. Soc. Japan, 70 , 813835.

    • Search Google Scholar
    • Export Citation
  • Kodama, Y-M., 1993: Large-scale common features of subtropical precipitation zones (the Baiu frontal zone, the SPCZ, the SACZ). Part II: Conditions of the circulations for generating the STCZs. J. Meteor. Soc. Japan, 71 , 581610.

    • Search Google Scholar
    • Export Citation
  • Li, J-L., A. Arakawa, and C. R. Mechoso, 1999: Improved simulation of PBL moist processes with the UCLA GCM. Preprints, Seventh Conf. on Climate Variations, Long Beach, CA, Amer. Meteor. Soc., 35–40.

    • Search Google Scholar
    • Export Citation
  • Liebmann, B., G. N. Kiladis, J. A. Marengo, T. Ambrizzi, and J. D. Glick, 1999: Submonthly convective variability over South America and the South Atlantic convergence zone. J. Climate, 12 , 18771891.

    • Search Google Scholar
    • Export Citation
  • Mechoso, C. R., J-Y. Yu, and A. Arakawa, 2000: A coupled GCM pilgrimage: From climate catastrophe to ENSO simulations. General Circulation Model Development: Past, Present and Future: Proceedings of a Symposium in Honor of Professor Akio Arakawa, D. A. Randall, Ed., Academic Press, 539–575.

    • Search Google Scholar
    • Export Citation
  • Namias, J., 1972: Influence of Northern Hemisphere general circulation on drought in northeastern Brazil. Tellus, 24 , 336342.

  • Nogués-Paegle, J., and K. C. Mo, 1997: Alternating wet and dry conditions over South America during summer. Mon. Wea. Rev., 125 , 279291.

    • Search Google Scholar
    • Export Citation
  • Paegle, J. N., L. A. Byerle, and K. C. Mo, 2000: Intraseasonal modulation of South American summer precipitation. Mon. Wea. Rev., 128 , 837850.

    • Search Google Scholar
    • Export Citation
  • Randall, D. A., and D. M. Pan, 1993: Implementation of the Arakawa–Schubert cumulus parameterization with a prognostic closure. The Representation of Cumulus Convection in Numerical Models of the Atmosphere, K. A. Emanuel and D. J. Raymond, Eds., Amer. Meteor. Soc., 137–144.

    • Search Google Scholar
    • Export Citation
  • 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 69, 13 pp.

    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., and T. M. Smith, 1994: Improved global sea surface temperature analyses using optimum interpolation. J. Climate, 7 , 929948.

    • Search Google Scholar
    • Export Citation
  • Robertson, A. W., and C. R. Mechoso, 1998: Interannual and decadal cycles in river flows of southeastern South America. J. Climate, 11 , 25702581.

    • Search Google Scholar
    • Export Citation
  • Robertson, A. W., and C. R. Mechoso, 2000: Interannual and interdecadal variability of the South Atlantic convergence zone. Mon. Wea. Rev., 128 , 29472957.

    • Search Google Scholar
    • Export Citation
  • Saravanan, R., and P. Chang, 2000: Interactions between tropical Atlantic variability and El Niño–Southern Oscillation. J. Climate, 13 , 21772194.

    • Search Google Scholar
    • Export Citation
  • Suarez, M. J., A. Arakawa, and D. A. Randall, 1983: The parameterization of the planetary boundary layer in the UCLA general circulation model: Formulation and results. Mon. Wea. Rev., 111 , 22242243.

    • Search Google Scholar
    • Export Citation
  • Tseng, L., and C. R. Mechoso, 2000: A quasi-biennial oscillation in the equatorial Atlantic Ocean. Geophys. Res. Lett., 28 , 187190.

  • Venegas, S. A., L. A. Mysak, and D. N. Straub, 1997: Atmosphere–ocean coupled variability in the South Atlantic. J. Climate, 10 , 29042920.

    • Search Google Scholar
    • Export Citation
  • Virji, H., 1981: A preliminary study of summertime tropospheric circulation patterns over South America estimated from cloud winds. Mon. Wea. Rev., 109 , 596610.

    • Search Google Scholar
    • Export Citation
  • Zebiak, S. E., 1993: Air–sea interaction in the equatorial Atlantic region. J. Climate, 6 , 15671586.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 407 167 8
PDF Downloads 190 71 3