• Berri, G. J., , P. L. Antico, , and L. Goddard, 2005: Evaluation of the climate outlook forum’s seasonal precipitation forecasts of southeast South America during 1998-2002. Int. J. Climatol., 25 , 365377.

    • Search Google Scholar
    • Export Citation
  • Casarin, D. P., , and V. E. Kousky, 1986: Anomalias de precipitação no sul do Brasil e variações na circulação atmosférica. Rev. Bras. Med., 1 , 8390.

    • 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 over Uruguay. J. Climate, 16 , 11591176.

    • Search Google Scholar
    • Export Citation
  • Chaves, R. R., , and P. Nobre, 2004: Interactions between sea surface temperature over the South Atlantic Ocean and the South Atlantic Convergence Zone. Geophys. Res. Lett., 31 , L03204. doi:10.1029/2003GL018647.

    • Search Google Scholar
    • Export Citation
  • Coelho, C. A. S., , S. Pezzulli, , M. Balmaseda, , F. J. Doblas-Reyes, , and D. B. Stephenson, 2004: Forecast calibration and combination: A simple Bayesian approach for ENSO. J. Climate, 17 , 15041516.

    • Search Google Scholar
    • Export Citation
  • Coelho, C. A. S., , D. B. Stephenson, , M. Balmaseda, , F. J. Doblas-Reyes, , and G. J. van Oldenborgh, 2006: Toward an integrated seasonal forecasting system for South America. J. Climate, 19 , 37043721.

    • Search Google Scholar
    • Export Citation
  • Díaz, A., , and P. Aceituno, 2003: Atmospheric circulation anomalies during episodes of enhanced and reduced convective cloudiness over Uruguay. J. Climate, 16 , 31713185.

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

    • Search Google Scholar
    • Export Citation
  • Doyle, M., , and V. Barros, 2002: Midsummer low-level circulation and precipitation in subtropical South America and related sea surface temperature anomalies in the South Atlantic. J. Climate, 15 , 33943410.

    • Search Google Scholar
    • Export Citation
  • Ferreira, R. N., , T. M. Rickenbach, , D. L. Herdies, , and L. M. V. Carvalho, 2003: Variability of South American convective cloud systems and tropospheric circulation during January–March 1998 and 1999. Mon. Wea. Rev., 131 , 961973.

    • Search Google Scholar
    • Export Citation
  • Goddard, L., , A. D. Barnston, , and S. J. Mason, 2003: Evaluation of the IRI’s “net assessment” seasonal climate forecasts 1997–2001. Bull. Amer. Meteor. Soc., 84 , 17611781.

    • Search Google Scholar
    • Export Citation
  • Grimm, A. M., 2003: The El Niño impact on the summer monsoon in Brazil: Regional processes versus remote influences. J. Climate, 16 , 263280.

    • Search Google Scholar
    • Export Citation
  • Grimm, A. M., , V. R. Barros, , and M. E. Doyle, 2000: Climate variability in southern South America associated with El Niño and La Niña events. J. Climate, 13 , 3558.

    • Search Google Scholar
    • Export Citation
  • Grimm, A. M., , J. S. Pal, , and F. Giorgi, 2007: Connection between spring conditions and peak summer monsoon rainfall in South America: Role of soil moisture, surface temperature, and topography in eastern Brazil. J. Climate, 20 , 59295945.

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

  • Liebmann, B., , G. N. Kiladis, , C. S. Vera, , A. C. Saulo, , and L. M. V. Carvalho, 2004: Subseasonal variations of rainfall in South America in the vicinity of the low-level jet east of the Andes and comparison to those in the South Atlantic convergence zone. J. Climate, 17 , 38293842.

    • Search Google Scholar
    • Export Citation
  • Mo, K. C., 2000: Relationships between low-frequency variability in the Southern Hemisphere and sea surface temperature anomalies. J. Climate, 13 , 35993610.

    • Search Google Scholar
    • Export Citation
  • Mo, K. C., , and J. N. Paegle, 2001: The Pacific–South American modes and their downstream effects. Int. J. Climatol., 21 , 12111229.

  • Montecinos, A., , A. Diaz, , and P. Aceituno, 2000: Seasonal diagnostic and predictability of rainfall in subtropical South America based on tropical Pacific SST. J. Climate, 13 , 746758.

    • Search Google Scholar
    • Export Citation
  • New, M., , M. Hulme, , and P. Jones, 1999: Representing twentieth-century space–time climate variability. Part I: Development of a 1961–90 mean monthly terrestrial climatology. J. Climate, 12 , 829856.

    • Search Google Scholar
    • Export Citation
  • New, M., , M. Hulme, , and P. Jones, 2000: Representing twentieth-century space–time climate variability. Part II: Development of monthly grids of terrestrial surface climate. J. Climate, 13 , 22172238.

    • Search Google Scholar
    • Export Citation
  • Paegle, J. N., , and K. C. Mo, 1997: Alternating wet and dry conditions over South America during summer. Mon. Wea. Rev., 125 , 279291.

  • Paegle, J. N., , and K. C. Mo, 2002: Linkages between summer rainfall variability over South America and sea surface temperature anomalies. J. Climate, 15 , 13891407.

    • Search Google Scholar
    • Export Citation
  • Paegle, J. N., and Coauthors, 2002: Progress in pan-American CLIVART research: Understanding the South American monsoon. Meteorologica, 27 , 332.

    • Search Google Scholar
    • Export Citation
  • Palmer, T. N., and Coauthors, 2004: The economic value of ensemble forecasts as a tool for risk assessment: From days to decades. Quart. J. Roy. Meteor. Soc., 128 , 747774.

    • 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
  • Robertson, A. W., , and C. R. Mechoso, 2003: Circulation regimes and low-frequency oscillations in the South Pacific sector. Mon. Wea. Rev., 131 , 15661576.

    • Search Google Scholar
    • Export Citation
  • Silva, G. A. M., , T. Ambrizzi, , and J. A. Marengo, 2009: Observational evidences on the modulation of the South American low level jet east of the Andes according the ENSO variability. Ann. Geophys., 27 , 645657.

    • Search Google Scholar
    • Export Citation
  • Smith, T. M., , and R. W. Reynolds, 2004: Improved extended reconstruction of SST (1854–1997). J. Climate, 17 , 24662477.

  • Wilks, D. S., 1995: Statistical Methods in the Atmospheric Sciences. Academic Press, 467 pp.

  • Zamboni, L., 2009: Relationships between upper level circulation over South America and rainfall over southeastern South America: A physical base for seasonal predictions. Ph.D. thesis, Universitá degli Studi di Trieste, 103 pp.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 23 23 4
PDF Downloads 12 12 1

Relationships between Upper-Level Circulation over South America and Rainfall over Southeastern South America: A Physical Base for Seasonal Predictions

View More View Less
  • 1 The Abdus Salam International Centre for Theoretical Physics, Earth System Physics Section, Dipartimento di Matematica, Universitá degli Studi di Trieste, Trieste, Italy, and Department of Atmospheric and Oceanic Science, University of California, Los Angeles, Los Angeles, California
  • | 2 Department of Atmospheric and Oceanic Science, University of California, Los Angeles, Los Angeles, California
  • | 3 The Abdus Salam International Centre for Theoretical Physics, Earth System Physics Section, Trieste, Italy
© Get Permissions
Restricted access

Abstract

The existence of a significant simultaneous correlation between bimonthly mean precipitation anomalies over southeastern South America (SESA) and either the first or the second (depending on season) leading mode of interannual variability of upper-level wind over South America (SA) is demonstrated during all seasons except winter. The pattern associated with these modes of variability is similar during all seasons and consists of a continental-scale vortex centered over the eastern coast of subtropical SA. The vortex has a quasi-barotropic structure during all seasons, and its variability modifies moisture transport from the South American low-level jet and the western tropical Atlantic to SESA thus creating precipitation anomalies in this region. During spring (October–November) and summer (January–February) the circulation creates a second center of precipitation anomalies over the South Atlantic convergence zone that are of opposite sign to those over SESA, while during fall (April–May) precipitation anomalies are primarily confined to SESA. On the basis of the correlation between upper-level winds and precipitation, an empirical method to produce long-range forecasts of bimonthly mean precipitation over SESA is developed. Method tests in hindcast mode for the period 1959–2001 show a potential for reliable predictions during the southern spring, summer, and fall. The method is further tested in an experimental mode by using Development of a European Multimodel Ensemble System for Seasonal-to-Interannual Prediction (DEMETER) wind hindcasts. Forecasts obtained in this way are skillful during spring only, with highest skill during El Niño–Southern Oscillation years. During summer and fall, the DEMETER forecasts of wind anomalies limit the method’s ability to make reliable real predictions.

Corresponding author address: Laura Zamboni, Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC), Viale Aldo Moro, 44 I-40127 Bologna, Italy. Email: laura.zamboni@cmcc.it

Abstract

The existence of a significant simultaneous correlation between bimonthly mean precipitation anomalies over southeastern South America (SESA) and either the first or the second (depending on season) leading mode of interannual variability of upper-level wind over South America (SA) is demonstrated during all seasons except winter. The pattern associated with these modes of variability is similar during all seasons and consists of a continental-scale vortex centered over the eastern coast of subtropical SA. The vortex has a quasi-barotropic structure during all seasons, and its variability modifies moisture transport from the South American low-level jet and the western tropical Atlantic to SESA thus creating precipitation anomalies in this region. During spring (October–November) and summer (January–February) the circulation creates a second center of precipitation anomalies over the South Atlantic convergence zone that are of opposite sign to those over SESA, while during fall (April–May) precipitation anomalies are primarily confined to SESA. On the basis of the correlation between upper-level winds and precipitation, an empirical method to produce long-range forecasts of bimonthly mean precipitation over SESA is developed. Method tests in hindcast mode for the period 1959–2001 show a potential for reliable predictions during the southern spring, summer, and fall. The method is further tested in an experimental mode by using Development of a European Multimodel Ensemble System for Seasonal-to-Interannual Prediction (DEMETER) wind hindcasts. Forecasts obtained in this way are skillful during spring only, with highest skill during El Niño–Southern Oscillation years. During summer and fall, the DEMETER forecasts of wind anomalies limit the method’s ability to make reliable real predictions.

Corresponding author address: Laura Zamboni, Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC), Viale Aldo Moro, 44 I-40127 Bologna, Italy. Email: laura.zamboni@cmcc.it

Save