• Aceituno, P., 1988: On the functioning of the Southern Oscillation in the South American sector. Mon. Wea. Rev., 116 , 505525.

  • Aceituno, P., , and A. Montecinos, 1993: Circulation anomalies associated with dry and wet periods in the South American Altiplano. Proc. Fourth Int. Conf. on Southern Hemisphere Meteorology, Hobart, Australia, Amer. Meteor. Soc., 330–331.

    • Search Google Scholar
    • Export Citation
  • Berbery, E. H., , and E. A. Collini, 2000: Springtime precipitation and water vapor flux over southeastern South America. Mon. Wea. Rev., 128 , 13281346.

    • 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 (Precipitation anomalies over Southern Brazil and variations in the atmospheric circulation). Rev. Bras. Meteor., 1 , 217231.

    • Search Google Scholar
    • Export Citation
  • Davidson, N. E., , J. L. McBride, , and B. J. McAvaney, 1983: The onset of the Australian monsoon during winter MONEX: Synoptic aspects. Mon. Wea. Rev., 111 , 496516.

    • Search Google Scholar
    • Export Citation
  • Davidson, N. E., , J. L. McBride, , and B. J. McAvaney, 1984: Divergent circulations during the onset of the 1978–79 Australian monsoon. Mon. Wea. Rev., 112 , 16841696.

    • Search Google Scholar
    • Export Citation
  • De Maria, M., 1985: Linear response of a stratified tropical atmosphere to convective forcing. J. Atmos. Sci., 42 , 19441969.

  • Figueroa, S. N., , and C. A. Nobre, 1990: Precipitation distribution over central and western tropical South America. Climanálise, 5 , 2540.

    • Search Google Scholar
    • Export Citation
  • Figueroa, S. N., , P. Satyamurty, , and P. L. Silva Dias, 1995: Simulations of the summer circulation over the South American region with an Eta coordinate model. J. Atmos. Sci., 52 , 15731584.

    • Search Google Scholar
    • Export Citation
  • Fu, R., , B. Zhu, , and R. Dickinson, 1999: How do atmosphere and land surface influence seasonal changes of convection in the tropical Amazon. J. Climate, 12 , 13061321.

    • Search Google Scholar
    • Export Citation
  • Gill, A. E., 1980: Some simple solutions for heat tropical circulation. Quart. J. Roy. Meteor. Soc., 106 , 447462.

  • Hendon, H. H., , and B. Liebmann, 1990: A composite study of onset of the Australian summer monsoon. J. Atmos. Sci., 47 , 22272240.

  • Holland, G. J., 1986: Interannual variability of the Australian monsoon at Darwin. Mon. Wea. Rev., 114 , 594604.

  • Horel, J. D., , A. N. Hahmann, , and J. E. Geisler, 1989: An investigation of the annual cycle of convective activity over the tropical Americas. J. Climate, 2 , 13881403.

    • Search Google Scholar
    • Export Citation
  • Jones, C., , and L. M. V. Carvalho, 2002: Active and break phases in the South American monsoon system. J. Climate, 15 , 905914.

  • Kalnay, E., and Coauthors, 1996: The NCEP/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, and the SACZ). Part I: Characteristics of subtropical frontal zones. J. Meteor. Soc. Japan, 70 , 813836.

    • Search Google Scholar
    • Export Citation
  • Koteswaram, P., 1958: The easterly jet stream in the Tropics. Tellus, 10 , 4357.

  • Kousky, V. E., 1979: Frontal influences on northeast Brazil. Mon. Wea. Rev., 107 , 11401153.

  • Kousky, V. E., 1985: Atmospheric circulation changes associated with rainfall anomalies over tropical Brazil. Mon. Wea. Rev., 113 , 19511957.

    • Search Google Scholar
    • Export Citation
  • Kousky, V. E., 1988: Pentad outgoing longwave radiation climatology for the South American sector. Rev. Bras. Meteor., 3 , 217231.

  • Kousky, V. E., , and M. A. Gan, 1981: Upper tropospheric cyclonic vortices in the tropical South Atlantic. Tellus, 33 , 538551.

  • Kousky, V. E., , and I. F. A. Cavalcanti, 1988: Precipitation and atmospheric circulation anomaly patterns in the South American sector. Rev. Bras. Meteor., 3 , 199206.

    • Search Google Scholar
    • Export Citation
  • Kousky, V. E., , and C. F. Ropelewski, 1989: Extremes in the Southern Oscillation and their relationship to precipitation anomalies with emphasis on the South American region. Rev. Bras. Meteor., 4 , 351363.

    • Search Google Scholar
    • Export Citation
  • Kousky, V. E., , and M. T. Kayano, 1994: Principal modes of outgoing longwave radiation and 250-mb circulation for the South American sector. J. Climate, 7 , 11311143.

    • Search Google Scholar
    • Export Citation
  • Kousky, V. E., , and C. F. Ropelewski, 1997: The Tropospheric Seasonally Varying Mean Climate over the Western Hemisphere (1979–1995). NCEP/Climate Prediction Center ATLAS, No. 3, 135 pp.

    • Search Google Scholar
    • Export Citation
  • Kousky, V. E., , M. T. Kagano, , and I. F. A. Cavalcanti, 1984: A review of the Southern Oscillation: Oceanic–atmospheric changes and related rainfall anomalies. Tellus, 36A , 490504.

    • Search Google Scholar
    • Export Citation
  • Krishnamurti, T. N., , and H. N. Bhalme, 1976: Oscillations of a monsoon system. Part I: Observational aspects. J. Atmos. Sci., 33 , 19371954.

    • 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
  • Madden, R. A., , and P. R. Julian, 1972: Description of global-scale circulation cells in the Tropics with a 40–50 day period. J. Atmos. Sci., 29 , 11091123.

    • Search Google Scholar
    • Export Citation
  • Marengo, J. A., , B. Liebmann, , V. E. Kousky, , N. P. Filizola, , and I. C. Wainer, 2001: Onset and end of the rainy season in the Brazilian Amazon basin. J. Climate, 14 , 833852.

    • Search Google Scholar
    • Export Citation
  • Matsuno, T., 1966: Quasi-geostrophic motions in the equatorial area. J. Meteor. Soc. Japan, 44 , 2542.

  • Murakami, T., , and A. Sumi, 1982: Southern Hemisphere summer monsoon circulation during the 1978/79 WMONEX. Part II: Onset, active and break monsoon. J. Meteor. Soc. Japan, 60 , 649671.

    • Search Google Scholar
    • Export Citation
  • Nicholls, N., , J. L. McBride, , and R. J. Ormerod, 1982: On predicting the onset of the Australian wet season at Darwin. Mon. Wea. Rev., 110 , 1417.

    • Search Google Scholar
    • Export Citation
  • 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
  • Ramage, C. S., 1971: Monsoon Meteorology. Academic Press, 296 pp.

  • Rao, G. V., , and S. Erdogan, 1989: The atmospheric heat source over the Bolivian plateau for a mean January. Bound.-Layer Meteor., 46 , 1333.

    • Search Google Scholar
    • Export Citation
  • Rao, V. B., , and K. Hada, 1990: Characteristics of rainfall over Brazil: Annual variations and connections with the Southern Oscillation. Theor. Appl. Climatol., 42 , 8192.

    • Search Google Scholar
    • Export Citation
  • Rao, V. B., , I. F. A. Cavalcanti, , and K. Hada, 1996: Annual variations of rainfall over Brazil and water vapor characteristics over South America. J. Geophys. Res., 101 , 2653926551.

    • Search Google Scholar
    • Export Citation
  • Ropelewski, C. F., , and M. S. Halpert, 1987: Global and regional scale precipitation patterns associated with the El Niño/Southern Oscillation. Mon. Wea. Rev., 115 , 16061626.

    • Search Google Scholar
    • Export Citation
  • Silva, V. B. S., , and V. E. Kousky, 2001: Variabilidade intrasazonal de precipitação sobre o leste do Brasil durante o verão de 1999/2000. (Intraseasonal variability of precipitation over eastern Brazil during the summer of 1999/2000). Rev. Bras. Meteor., 16 , 187199.

    • Search Google Scholar
    • Export Citation
  • Silva Dias, P. L., , W. Schubert, , and M. De Maria, 1983: Large-scale response of the tropical atmosphere to transient convection. J. Atmos. Sci., 40 , 26892707.

    • Search Google Scholar
    • Export Citation
  • Silva Dias, P. L., , J. P. Bonatti, , and V. E. Kousky, 1987: Diurnally forced tropical tropospheric circulation over South America. Mon. Wea. Rev., 115 , 14651478.

    • Search Google Scholar
    • Export Citation
  • Troup, A. J., 1961: Variation in upper-tropospheric flow associated with the onset of the Australian summer monsoon. Indian J. Meteor. Geophys., 12 , 217230.

    • 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 , 599610.

    • Search Google Scholar
    • Export Citation
  • Weickmann, K. M., 1983: Intraseasonal circulation and outgoing longwave radiation modes during Northern Hemisphere winter. Mon. Wea. Rev., 111 , 18381858.

    • Search Google Scholar
    • Export Citation
  • Weickmann, K. M., , G. R. Lussky, , and J. E. Kutzbach, 1985: Intraseasonal (30–60 day) fluctuations of outgoing longwave radiation and 250 mb streamfunction during Northern Winter. Mon. Wea. Rev., 113 , 941961.

    • Search Google Scholar
    • Export Citation
  • WMO, 1998: CLIVAR initial implementation plan. International CLIVAR Project Office, WCRP No. 103, WMO/TD No. 869, ICPO No. 14, 356 pp.

  • Zhou, J., , and K-M. Lau, 1998: Does a monsoon climate exist over South America? J. Climate, 11 , 10201040.

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The South America Monsoon Circulation and Its Relationship to Rainfall over West-Central Brazil

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  • 1 National Institute for Space Research (INPE) of Brazil, Sao Paulo, Brazil
  • | 2 National Centers for Environmental Prediction, Camp Springs, Maryland
  • | 3 International Research Institute for Climate Prediction, Palisades, New York
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Abstract

The mean atmospheric circulation for the rainy season over west-central Brazil (20°–10°S, 60°–50°W) is investigated for a 21-yr period (July 1979–June 2000). The NCEP–NCAR reanalysis, pentad outgoing longwave radiation (OLR), and daily gridded precipitation analyses from NCEP are used in this study. The analysis presented here provides an improved description of the mean annual cycle based on daily and pentad (5-day) rainfall and atmospheric circulation data. The pentad precipitation averaged for the study region shows a rapid increase during the spring months (September–November) and a rapid decrease in April. The rainiest period (more than 8 mm day−1) is from December to February. There are distinct wet (7 months) and dry (5 months) seasons, with approximately 90% of the total annual rainfall occurring during October–April.

The rainy season begins following the period when temperature is at its seasonal maximum. The pre-rainy-season warmth acts to destabilize the atmosphere and to create a reversal in the low-latitude temperature gradient. This results in a reversal of the vertical shear of the zonal wind from increasing (decreasing) westerly (easterly) winds with height to decreasing (increasing) westerly (easterly) winds with height. The examination of the vertical structure of the average zonal wind over the area reveals that prior to the onset of the rainy season easterlies prevail in the lower troposphere (up to 600 hPa) and westerly winds prevail at upper levels with maximum speed in the layer 200–150 hPa. During the rainy season the vertical structure of zonal wind is opposite to that of winter (June–August).

Within each rainy season, west-central Brazil experiences anomalously wet and dry periods. Wet periods are associated with low-level northwesterly and westerly flow east of the Andes that converges on west-central Brazil. Dry periods are associated with enhanced northwesterly flow over Paraguay and northern Argentina, and easterly anomalies over west-central Brazil.

Corresponding author address: Dr. M. A. Gan, INPE, CP515, 12201-970 Sao Jose dos Campos, Sao Paulo, Brazil. Email: alonso@cptec.inpe.br

Abstract

The mean atmospheric circulation for the rainy season over west-central Brazil (20°–10°S, 60°–50°W) is investigated for a 21-yr period (July 1979–June 2000). The NCEP–NCAR reanalysis, pentad outgoing longwave radiation (OLR), and daily gridded precipitation analyses from NCEP are used in this study. The analysis presented here provides an improved description of the mean annual cycle based on daily and pentad (5-day) rainfall and atmospheric circulation data. The pentad precipitation averaged for the study region shows a rapid increase during the spring months (September–November) and a rapid decrease in April. The rainiest period (more than 8 mm day−1) is from December to February. There are distinct wet (7 months) and dry (5 months) seasons, with approximately 90% of the total annual rainfall occurring during October–April.

The rainy season begins following the period when temperature is at its seasonal maximum. The pre-rainy-season warmth acts to destabilize the atmosphere and to create a reversal in the low-latitude temperature gradient. This results in a reversal of the vertical shear of the zonal wind from increasing (decreasing) westerly (easterly) winds with height to decreasing (increasing) westerly (easterly) winds with height. The examination of the vertical structure of the average zonal wind over the area reveals that prior to the onset of the rainy season easterlies prevail in the lower troposphere (up to 600 hPa) and westerly winds prevail at upper levels with maximum speed in the layer 200–150 hPa. During the rainy season the vertical structure of zonal wind is opposite to that of winter (June–August).

Within each rainy season, west-central Brazil experiences anomalously wet and dry periods. Wet periods are associated with low-level northwesterly and westerly flow east of the Andes that converges on west-central Brazil. Dry periods are associated with enhanced northwesterly flow over Paraguay and northern Argentina, and easterly anomalies over west-central Brazil.

Corresponding author address: Dr. M. A. Gan, INPE, CP515, 12201-970 Sao Jose dos Campos, Sao Paulo, Brazil. Email: alonso@cptec.inpe.br

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