• Ambrizzi, T., and B. J. Hoskins, 1997: Stationary Rossby-wave propagation in a baroclinic atmosphere. Quart. J. Roy. Meteor. Soc, 123 , 919928.

    • Search Google Scholar
    • Export Citation
  • Berbery, E. H., J. Nogués-Paegle, and J. Horel, 1992: Wavelike Southern Hemisphere extratropical teleconnections. J. Atmos. Sci, 49 , 155177.

    • Search Google Scholar
    • Export Citation
  • Berri, G. J., and J. Inzunza B, 1993: The effect of the low-level jet on the poleward water vapour transport in the central region of South America. Atmos. Environ, 27A , 335341.

    • Search Google Scholar
    • Export Citation
  • Bonner, W. D., 1968: Climatology of the low level jet. Mon. Wea. Rev, 96 , 833850.

  • Brooks, C. E. P., and N. Carruthers, 1953: Handbook of Statistical Methods in Meteorology. Her Majesty's Stationary Office, 412 pp.

  • Campetella, C., and C. Vera, 2002: The influence of the Andes Mountains on the South American low-level flow. Geophys. Res. Lett, 29, 1826, doi:10.1029/2002GL015451.

    • Search Google Scholar
    • Export Citation
  • Carvalho, L. M. V., C. Jones, and B. Liebmann, 2004: The South Atlantic convergence zone: Intensity, form, persistence, and relationships with intraseasonal to interannual activity and extreme rainfall. J. Climate, 17 , 88108.

    • Search Google Scholar
    • Export Citation
  • Casarin, D. P., and V. E. Kousky, 1986: Anomalias de precipitacão no sul do Brasil e variacoes na circulacão atmosferica. Rev. Bras. Meteor, 1 , 8390.

    • Search Google Scholar
    • Export Citation
  • Douglas, M. W., M. Nicolini, and C. Saulo, 1998: Observational evidences of a low level jet east of the Andes during January– March 1998. Meteorologica, 23 , 6372.

    • Search Google Scholar
    • Export Citation
  • Douglas, M. W., M. Peña, and W. R. Villarpando, 2000: Special observations of the low-level flow over eastern Bolivia during the 1999 Atmospheric Mesoscale Campaign. Preprints, Sixth Int. Conf. on Southern Hemisphere Meteorology and Oceanography, Santiago, Chile, Amer. Meteor. Soc., 157–158.

    • Search Google Scholar
    • Export Citation
  • Ferranti, L., T. N. Palmer, F. Molteni, and E. Klinker, 1990: Tropical– extratropical interaction associated with the 30–60 day oscillation and its impact on medium and extended range prediction. J. Atmos. Sci, 47 , 21772199.

    • Search Google Scholar
    • Export Citation
  • Figueroa, S. N., P. Satyamurty, and P. L. da 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
  • Garreaud, R. D., and J. M. Wallace, 1998: Summertime incursions of midlatitude air into subtropical and tropical South America. Mon. Wea. Rev, 126 , 27132733.

    • Search Google Scholar
    • Export Citation
  • Hendon, H. H., and M. L. Salby, 1994: The life cycle of the Madden– Julian oscillation. J. Atmos. Sci, 51 , 22252237.

  • Herdies, D. L., A. da Silva, M. A. F. Silva Dias, and R. Nieto Ferreira, 2002: Moisture budget of the bimodal pattern of the summer circulation over South America. J. Geophys. Res.,107, 8075, doi:10.1029/2001JD000997.

    • 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.

  • Jones, C., L. M. V. Carvalho, R. W. Higgins, D. E. Waliser, and J-K. Schemm, 2004: A statistical forecast model of tropical intraseasonal convective anomalies. J. Climate, 17 , 20782095.

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

  • Kiladis, G. N., and K. M. Weickmann, 1992: Circulation anomalies associated with tropical convection during northern winter. Mon. Wea. Rev, 120 , 19001923.

    • Search Google Scholar
    • Export Citation
  • Knutson, T. R., and K. M. Weickmann, 1987: 30–60 day atmospheric oscillations: Composite life cycles of convection and circulation anomalies. Mon. Wea. Rev, 115 , 14071436.

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

    • Search Google Scholar
    • Export Citation
  • Lenters, J. D., and K. H. Cook, 1999: Summertime precipitation variability over South America: Role of the large-scale circulation. Mon. Wea. Rev, 127 , 409431.

    • Search Google Scholar
    • Export Citation
  • Li, Z. X., and H. Le Treut, 1999: Transient behavior of the meridional moisture transport across South America and its relation to atmospheric circulation patterns. Geophys. Res. Lett, 26 , 14091412.

    • 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
  • Liebmann, B., C. Jones, and L. M. V. de Carvalho, 2001: Interannual variability of daily extreme precipitation events in the state of São Paulo, Brazil. J. Climate, 14 , 208218.

    • Search Google Scholar
    • Export Citation
  • Livezey, R. E., and W. Y. Chen, 1983: Statistical field significance and its determination by Monte Carlo techniques. Mon. Wea. Rev, 111 , 4659.

    • Search Google Scholar
    • Export Citation
  • Madden, R. A., and P. R. Julian, 1994: Observations of the 40–50-day oscillation—A review. Mon. Wea. Rev, 122 , 814837.

  • Marengo, J. A., M. W. Douglas, and P. L. Silva Dias, 2002: The South American low-level jet east of the Andes during the 1999 LBA-TRMM and LBA-WET AMC campaign. J. Geophys. Res.,107, 8079, doi:10.1029/2001JD001188.

    • Search Google Scholar
    • Export Citation
  • Marton, E., and P. L. Silva Dias, 2001: Variabilidade intrasazonal na Zona de Convergência do Atlântico Sul. IX Congreso Latinoamericano e lberico de Meteorología y VIII Congreso Argentino de Meteorología: La Meteorología y el Medio Ambiente en el Siglo XXI, Buenos Aires, Argentina, ANAIS DIGITAIS, CD-ROM, 5.A.25–179.

    • Search Google Scholar
    • Export Citation
  • Mo, K. C., and R. W. Higgins, 1996: Large-scale atmospheric moisture transport as evaluated in the NCEP/NCAR and the NASA/ DAO reanalyses. J. Climate, 9 , 15311545.

    • Search Google Scholar
    • Export Citation
  • Nicolini, M., and A. C. Saulo, 2000: ETA characterization of the 1997–98 warm season Chaco jet cases. Preprints, Sixth Int. Conf. on Southern Hemisphere Meteorology and Oceanography, Santiago, Chile, Amer. Meteor. Soc., 330–331.

    • Search Google Scholar
    • Export Citation
  • Nieto Ferreira, R., 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
  • 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., 2000: American low-level jets in observation and theory: The ALLS project. Preprints, Sixth Int. Conf. on Southern Hemisphere Meteorology and Oceanography, Santiago, Chile, Amer. Meteor. Soc., 161–162.

    • 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
  • Salby, M. L., and H. H. Hendon, 1994: Intraseasonal behavior of clouds, temperature, and motion in the Tropics. J. Atmos. Sci, 51 , 22072224.

    • Search Google Scholar
    • Export Citation
  • Salio, P., M. Nicolini, and A. C. Saulo, 2002: Chaco low-level jet events characterization during the austral summer season. J. Geophys. Res.,107, 4816, doi:10.1029/2001JD001315.

    • Search Google Scholar
    • Export Citation
  • Saulo, A. C., and M. Nicolini, 2000: The atmospheric conditions preceding the occurrence of a strong low level jets east of the Andes during January 1998. Preprints, Sixth Int. Conf. on Southern Hemisphere Meteorology and Oceanography, Santiago, Chile, Amer. Meteor. Soc., 336–337.

    • Search Google Scholar
    • Export Citation
  • Silva Dias, P. L., 2000: The role of latent heat release in the dynamics of the LLJ's along the Andes. Preprints, Sixth Int. Conf. on Southern Hemisphere Meteorology and Oceanography, Santiago, Chile, Amer. Meteor. Soc., 163–164.

    • Search Google Scholar
    • Export Citation
  • Stensrud, D. J., 1996: Importance of low-level jets to climate: A review. J. Climate, 9 , 16981711.

  • Sugahara, S., R. P. da Rocha, and M. L. Rodrigues, 1994: Atmospheric conditions associated with the South America low level jet (in Portuguese). Proc. Eighth Brazilian Congress of Meteorology, Vol. 2, Belo Horizonte, Brazil, Brazilian Meteorological Society, 573–577.

    • Search Google Scholar
    • Export Citation
  • Vera, C., P. K. Vigliarolo, and E. H. Berbery, 2002: Cold season synoptic-scale waves over subtropical South America. Mon. Wea. Rev, 130 , 684699.

    • Search Google Scholar
    • Export Citation
  • Wheeler, M., and G. N. Kiladis, 1999: Convectively coupled equatorial waves: Analysis of clouds and temperature in the wavenumber–frequency domain. J. Atmos. Sci, 56 , 374399.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 457 165 13
PDF Downloads 293 138 14

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

View More View Less
  • 1 NOAA–CIRES Climate Diagnostics Center, Boulder, Colorado
  • | 2 NOAA Aeronomy Laboratory, Boulder, Colorado
  • | 3 Centro de Investigaciones del Mar y la Atmósfera/CONICET, Departamento de Ciencias de la Atmósfera y los Océanos, Universidad de Buenos Aires, Buenos Aires, Argentina
  • | 4 Department of Atmospheric Sciences, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo, São Paulo, Brazil
Restricted access

Abstract

Regional and large-scale circulation anomalies associated with variations in rainfall downstream of the South American low-level jet are identified and compared to those in the South Atlantic convergence zone (SACZ). Composites of precipitation associated with strong jets reveal an approximate doubling of the quantities one would expect from climatology, with an evolution of the rainfall pattern from south to north. The occurrence of extreme precipitation events follows a similar pattern. Meridional cross sections of composite wind reveal a distinct low-level jet near 20°S and a baroclinic development farther south that appears to force the jet. Geopotential height, temperature, and large-scale wind composites suggest that this developing disturbance is tied to a wave train that originates in the midlatitude Pacific and turns equatorward as it crosses the Andes Mountains. Similar composites based on SACZ rainfall reveal similar features, but of opposite sign, suggesting that the phase of the wave as it crosses the Andes Mountains determines whether rainfall will be enhanced downstream of the jet or in the SACZ. The alternate suppression or enhancement of rainfall in these adjacent regions results in a precipitation “dipole.” Many previous studies have found a similar out-of-phase relationship over many time scales. The phase of the Madden–Julian oscillation (MJO) is composited relative to anomalous precipitation events, revealing statistically relevant amplitudes associated with rainfall both downstream of the jet and in the SACZ. The MJO is a particularly interesting intraseasonal oscillation because it has some predictability. It is speculated that the slowly varying dipole that has been observed is a consequence of the preferred phasing of synoptic waves due to variations of the planetary-scale basic-state flow, which is at times associated with the MJO.

Corresponding author address: Dr. Brant Liebmann, NOAA–CIRES Climate Diagnostics Center, R/CDC1, 325 Broadway, Boulder, CO 80305-3328. Email: Brant.Liebmann@noaa.gov

Abstract

Regional and large-scale circulation anomalies associated with variations in rainfall downstream of the South American low-level jet are identified and compared to those in the South Atlantic convergence zone (SACZ). Composites of precipitation associated with strong jets reveal an approximate doubling of the quantities one would expect from climatology, with an evolution of the rainfall pattern from south to north. The occurrence of extreme precipitation events follows a similar pattern. Meridional cross sections of composite wind reveal a distinct low-level jet near 20°S and a baroclinic development farther south that appears to force the jet. Geopotential height, temperature, and large-scale wind composites suggest that this developing disturbance is tied to a wave train that originates in the midlatitude Pacific and turns equatorward as it crosses the Andes Mountains. Similar composites based on SACZ rainfall reveal similar features, but of opposite sign, suggesting that the phase of the wave as it crosses the Andes Mountains determines whether rainfall will be enhanced downstream of the jet or in the SACZ. The alternate suppression or enhancement of rainfall in these adjacent regions results in a precipitation “dipole.” Many previous studies have found a similar out-of-phase relationship over many time scales. The phase of the Madden–Julian oscillation (MJO) is composited relative to anomalous precipitation events, revealing statistically relevant amplitudes associated with rainfall both downstream of the jet and in the SACZ. The MJO is a particularly interesting intraseasonal oscillation because it has some predictability. It is speculated that the slowly varying dipole that has been observed is a consequence of the preferred phasing of synoptic waves due to variations of the planetary-scale basic-state flow, which is at times associated with the MJO.

Corresponding author address: Dr. Brant Liebmann, NOAA–CIRES Climate Diagnostics Center, R/CDC1, 325 Broadway, Boulder, CO 80305-3328. Email: Brant.Liebmann@noaa.gov

Save