Editorial Type:
Article
Article Type:
Research Article

Atmospheric Circulation Associated with Persistent Generalized Frosts in Central-Southern South America

Gabriela V. Müller Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, Brazil

Search for other papers by Gabriela V. Müller in
Current site
Google Scholar
PubMed Close
and
Guillermo J. Berri Departamento de Ciencias de la Atmósfera y los Océanos, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina

Search for other papers by Guillermo J. Berri in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Apr 2007
DOI:
https://doi.org/10.1175/MWR3344.1
Page(s):
1268–1289
Restricted access

Abstract

This paper describes the large-scale atmospheric circulation associated with persistent generalized frosts (GFs; at least 75% of the stations report frosts) in the east-central region of Argentina known as the Wet Pampa. The GF events are grouped according to their persistence, and NCEP–NCAR reanalysis data are used to create daily composites of mass and wind field anomalies during the 1961–90 winters. The GFs are caused by an anticyclonic anomaly that enters South America, generating southerly wind anomalies and cold air advection that are strengthened by the meridional layout of a cyclonic anomaly over the South Atlantic Ocean. In the case of the more persistent events the wind anomaly grows during the previous days and becomes quasi-stationary. Also, the study identifies at 250 hPa a double train of eastward-moving Rossby waves along the subtropical and subpolar latitudes, respectively, of the Southern Hemisphere. The layout of both wave trains favors the development of an intense southerly wind anomaly in the entire southern cone of the continent. On the other hand, the propagation pattern during the less persistent GFs shows only one arc-shaped Rossby wave train that reaches South America, and then propagates northeastward. Additionally, there is a subtropical jet entrance/confluence over the western side of the continent that induces a secondary meridional circulation whose subsiding branch facilitates the equatorward displacement of the low-level anticyclone, particularly in the case of the less persistent events. In the case of the more persistent GFs the confluence is located farther east and sustains essentially zonal wave train propagation, so that the surface anticyclone is not able to achieve a major equatorward penetration.

* Additional affiliation: Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina (CONICET), Buenos Aires, Argentina

Corresponding author address: Gabriela V. Müller, Departamento de Ciências Atmosféricas Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, Brazil. Email: gabriela@model.iag.usp.br

Abstract

This paper describes the large-scale atmospheric circulation associated with persistent generalized frosts (GFs; at least 75% of the stations report frosts) in the east-central region of Argentina known as the Wet Pampa. The GF events are grouped according to their persistence, and NCEP–NCAR reanalysis data are used to create daily composites of mass and wind field anomalies during the 1961–90 winters. The GFs are caused by an anticyclonic anomaly that enters South America, generating southerly wind anomalies and cold air advection that are strengthened by the meridional layout of a cyclonic anomaly over the South Atlantic Ocean. In the case of the more persistent events the wind anomaly grows during the previous days and becomes quasi-stationary. Also, the study identifies at 250 hPa a double train of eastward-moving Rossby waves along the subtropical and subpolar latitudes, respectively, of the Southern Hemisphere. The layout of both wave trains favors the development of an intense southerly wind anomaly in the entire southern cone of the continent. On the other hand, the propagation pattern during the less persistent GFs shows only one arc-shaped Rossby wave train that reaches South America, and then propagates northeastward. Additionally, there is a subtropical jet entrance/confluence over the western side of the continent that induces a secondary meridional circulation whose subsiding branch facilitates the equatorward displacement of the low-level anticyclone, particularly in the case of the less persistent events. In the case of the more persistent GFs the confluence is located farther east and sustains essentially zonal wave train propagation, so that the surface anticyclone is not able to achieve a major equatorward penetration.

* Additional affiliation: Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina (CONICET), Buenos Aires, Argentina

Corresponding author address: Gabriela V. Müller, Departamento de Ciências Atmosféricas Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, Brazil. Email: gabriela@model.iag.usp.br

Save
Cover Monthly Weather Review
Monthly Weather Review

  • Algarve, V. R., and I. Cavalcanti, 1994: Características da circulação atmosférica associadas a ocorrência de geadas no sul do Brasil (Atmospheric circulation characteristics associated with frost occurrence in southern Brazil). Preprints, Sétimo Congresso Brasileiro de Meteorologia, Belo Horizonte, Brazil, Sociedade Brasileira de Meterologia, 545–547.

  • Ambrizzi, T., B. J. Hoskins, and H-H. Hsu, 1995: Rossby wave propagation and teleconnection patterns in the austral winter. J. Atmos. Sci., 52 , 3661–3672.

    • Search Google Scholar
    • Export Citation

  • Berbery, E. H., and C. S. Vera, 1996: Characteristics of the Southern Hemisphere winter storm track with filtered and unfiltered data. J. Atmos. Sci., 53 , 468–481.

    • Search Google Scholar
    • Export Citation

  • Cavalcanti, I., and M. T. Kayano, 1999: High frequency patterns of the atmospheric circulation over the Southern Hemisphere and South American. Meteor. Atmos. Phys., 69 , 179–193.

    • Search Google Scholar
    • Export Citation

  • Escobar, G. C. J., R. H. Compagnucci, and S. A. Bischoff, 2004: Sequence patterns of 1000 hPa and 500 hPa geopotential height fields associated with cold surges in Buenos Aires. Atmósfera, 12 , 2. 69–89.

    • Search Google Scholar
    • Export Citation

  • Fortune, M. A., and V. E. Kousky, 1983: Two severe freezes in Brazil: Precursors and synoptic evolution. Mon. Wea. Rev., 111 , 181–196.

    • Search Google Scholar
    • Export Citation

  • Gan, M. A., and V. B. Rao, 1994: The influence of the Andes Cordillera on transient disturbances. Mon. Wea. Rev., 122 , 1141–1157.

  • Garreaud, R. D., 1999: Cold air incursions over subtropical and tropical South America: A numerical case of study. Mon. Wea. Rev., 127 , 2823–2853.

    • Search Google Scholar
    • Export Citation

  • Garreaud, R. D., 2000: Cold air incursions over subtropical South America: Mean structure and dynamics. Mon. Wea. Rev., 128 , 2544–2559.

    • Search Google Scholar
    • Export Citation

  • Haddock, D., R. Motta, R. McInturff, M. Halpert, and R. Smelser, 1981: Freeze hits Brazilian coffee area on July 20 and 21, 1981. Weekly Weather and Crop Bulletin, Vol. 68, No. 30, 25–27.

  • Hoskins, B. J., 1983: Dynamical processes in the atmosphere and the use of models. Quart. J. Roy. Meteor. Soc., 109 , 1–21.

  • Kousky, V., and I. Cavalcanti, 1997: The principal modes of high frequency variability over the South American region. Preprints, Fifth Int. Conf. on Southern Hemisphere Meteorology and Oceanography, Pretoria, South Africa, Amer. Meteor. Soc., 226–227.

  • Krishnamurti, T. N., M. Tewari, D. R. Chakraborty, J. A. Marengo, P. L. Silva Dias, and P. Satyamurti, 1999: Downstream amplification: A possible precursor to major freeze events over south-eastern Brazil. Wea. Forecasting, 14 , 242–270.

    • Search Google Scholar
    • Export Citation

  • Lau, K. M., and C. P. Chang, 1987: Planetary scale aspects of the winter monsoon and atmospheric teleconnection. Monsoon Meteorology, C. P. Chang and T. N. Krishnamurti, Eds., Oxford University Press, 171–202.

    • Search Google Scholar
    • Export Citation

  • Lichtenstein, E., 1989: Some influences of the Andes Cordillera on the synoptic scale circulation. Preprints, Third Int. Conf. on Southern Hemisphere Meteorology and Oceanography, Buenos Aires, Argentina, Amer. Meteor. Soc., 156–159.

  • Marengo, J. A., A. Cornejo, P. Satyamurty, C. Nobre, and W. Sea, 1997: Cold surges in tropical and extratropical South America: The strong event in June 1994. Mon. Wea. Rev., 125 , 2759–2786.

    • Search Google Scholar
    • Export Citation

  • Müller, G. V., M. N. Núñez, and M. E. Seluchi, 2000: Relationship between ENSO cycles and frost events within the Pampa Humeda region. Int. J. Climatol., 20 , 1619–1637.

    • Search Google Scholar
    • Export Citation

  • Müller, G. V., T. Ambrizzi, M. N. Nuñez, and S. Ferraz, 2003a: Teleconnection between tropical west Pacific convection and cold surges in the southern South America during austral winter. Preprints, Seventh Int. Conf. on Southern Hemisphere Meteorology and Oceanography, Wellington, New Zealand, Amer. Meteor. Soc., CD-ROM, P1.19.

  • Müller, G. V., R. H. Compagnucci, M. N. Núñez, and M. A. Salles, 2003b: Surface circulation associated with frost in the Wet Pampas. Int. J. Climatol., 23 , 943–962.

    • Search Google Scholar
    • Export Citation

  • Müller, G. V., T. Ambrizzi, and M. N. Nuñez, 2005: Mean atmospheric circulation leading to generalized frosts in central southern South America. Theor. Appl. Climatol., 82 , 95–112.

    • Search Google Scholar
    • Export Citation

  • Satyamurty, P., C. A. Nobre, and P. L. Silva Dias, 1998: Meteorology of the Southern Hemisphere. Amer. Meteor. Soc., 411 pp.

  • Schultz, D., W. E. Bracken, L. Bosart, G. Hakim, M. Bedrick, M. Dickinson, and K. Tyle, 1998: Planetary- and synoptic-scale signature associated with Central American cold surges. Mon. Wea. Rev., 126 , 5–27.

    • Search Google Scholar
    • Export Citation

  • Seluchi, M. E., and J. A. Marengo, 2000: Tropical–midlatitude exchange of air masses during summer and winter in South America: Climatic aspects and examples of intense events. Int. J. Climatol., 20 , 1167–1190.

    • Search Google Scholar
    • Export Citation

  • Seluchi, M. E., Y. V. Serafini, and H. Le Treut, 1998: The impact of the Andes on transient atmospheric systems: A comparison between observations and GCM results. Mon. Wea. Rev., 126 , 895–912.

    • Search Google Scholar
    • Export Citation

  • Uccellini, L. W., and D. R. Johnson, 1979: The coupling of upper and lower tropospheric jet streaks and implications in development of severe convective storms. Mon. Wea. Rev., 107 , 682–703.

    • Search Google Scholar
    • Export Citation

  • Vera, C. S., and P. K. Vigliarolo, 2000: A diagnostic study of cold-air outbreaks over South America. Mon. Wea. Rev., 128 , 3–24.

  • Vera, C. S., P. K. Vigliarolo, and E. H. Berbery, 2002: Cold season waves over subtropical South America. Mon. Wea. Rev., 130 , 684–699.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 376 79 5
PDF Downloads 181 53 4