Editorial Type:
Article
Article Type:
Research Article

Cold Season Synoptic-Scale Waves over Subtropical South America

Carolina S. Vera CIMA/Departamento de Ciencias de la Atmósfera, Universidad de Buenos Aires–CONICET, Buenos Aires, Argentina

Search for other papers by Carolina S. Vera in
Current site
Google Scholar
PubMed Close
,
Paula K. Vigliarolo CADIC–CONICET, Ushuaia, Argentina

Search for other papers by Paula K. Vigliarolo in
Current site
Google Scholar
PubMed Close
, and
Ernesto Hugo Berbery Department of Meteorology, University of Maryland, College Park, College Park, Maryland

Search for other papers by Ernesto Hugo Berbery in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Mar 2002
DOI:
https://doi.org/10.1175/1520-0493(2002)130<0684:CSSSWO>2.0.CO;2
Page(s):
684–699
Restricted access

Abstract

The most active winter synoptic-scale wave patterns over South America are identified using an extended empirical orthogonal function (EEOF) technique and are physically diagnosed using composite methods. Results show that the leading modes of short timescale variability propagate along two main paths: over the subtropical jet latitudes (∼30°S) and over the subpolar jet latitudes (∼60°S). This research focuses on the subtropical mode and its evolution over South America.

The observed structure of the systems associated with the subtropical mode resembles that of midlatitude baroclinic waves. Both cyclonic and anticyclonic perturbations display significant modifications in their three-dimensional structure as they evolve over extratropical and subtropical South America. While the upper-level perturbations are mostly unaffected when moving eastward, the lower-level perturbations advance following the shape of the Andes Mountains and exhibit an abrupt equatorward migration at the lee side of the mountains. As a result of such detachment, smaller eddy heat fluxes are observed in the vicinity of the orography and consequently a weaker eddy baroclinic growth is observed. Once the upper-level system is on the lee side, the perturbations acquire a more typical baroclinic wave structure and low-level intensification of the system occurs. The latter is largest around 1000 km east of the orography, where enhanced moisture transports from tropical latitudes along the eastern portion of the low-level cyclone favor precipitation occurrence over southeastern South America. Those precipitation processes seem to provide a diabatic source of energy that further contributes to the strengthening of the low-level cyclone. In addition, an intensification of the cyclone once over the ocean was found in 60% of the situations considered, which is consistent with previous research suggesting an additional source of moisture and heat flux due to the warm waters of the Brazil Current.

Corresponding author address: Dr. Carolina S. Vera, CIMA, Pab. 2, 2do Piso, Ciudad Universitaria, 1428 Buenos Aires, Argentina. Email: carolina@at.fcen.uba.ar

Abstract

The most active winter synoptic-scale wave patterns over South America are identified using an extended empirical orthogonal function (EEOF) technique and are physically diagnosed using composite methods. Results show that the leading modes of short timescale variability propagate along two main paths: over the subtropical jet latitudes (∼30°S) and over the subpolar jet latitudes (∼60°S). This research focuses on the subtropical mode and its evolution over South America.

The observed structure of the systems associated with the subtropical mode resembles that of midlatitude baroclinic waves. Both cyclonic and anticyclonic perturbations display significant modifications in their three-dimensional structure as they evolve over extratropical and subtropical South America. While the upper-level perturbations are mostly unaffected when moving eastward, the lower-level perturbations advance following the shape of the Andes Mountains and exhibit an abrupt equatorward migration at the lee side of the mountains. As a result of such detachment, smaller eddy heat fluxes are observed in the vicinity of the orography and consequently a weaker eddy baroclinic growth is observed. Once the upper-level system is on the lee side, the perturbations acquire a more typical baroclinic wave structure and low-level intensification of the system occurs. The latter is largest around 1000 km east of the orography, where enhanced moisture transports from tropical latitudes along the eastern portion of the low-level cyclone favor precipitation occurrence over southeastern South America. Those precipitation processes seem to provide a diabatic source of energy that further contributes to the strengthening of the low-level cyclone. In addition, an intensification of the cyclone once over the ocean was found in 60% of the situations considered, which is consistent with previous research suggesting an additional source of moisture and heat flux due to the warm waters of the Brazil Current.

Corresponding author address: Dr. Carolina S. Vera, CIMA, Pab. 2, 2do Piso, Ciudad Universitaria, 1428 Buenos Aires, Argentina. Email: carolina@at.fcen.uba.ar

Save
Cover Monthly Weather Review
Monthly Weather Review

  • Bannon, P. R., 1992: A model of Rocky Mountain lee cyclogenesis. J. Atmos. Sci, 49 , 1510–1522.

  • Berbery, E. H., and M. N. Nunez, 1987: Ciclogenesis al este de los Andes: Influencia dinamica de la cordillera en su desarrdlo (Cyclogenesis east of the Andes: Dynamical influences during its development). Proc. Second Int. American Conf. of Meteorology, Buenos Aires, Argentina, Federacion Latinoamericana de Sociedades de Meterologia, 21–27.

    • 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

  • Berbery, E. H., and E. A. Collini, 2000: Springtime precipitation and water vapor flux over southeastern South America. Mon. Wea. Rev, 128 , 1328–1346.

    • Search Google Scholar
    • Export Citation

  • Blackmon, M. L., R. A. Madden, J. M. Wallace, and D. S. Gutzler, 1979: Geographical variations in the vertical structure of geopotential height fluctuations. J. Atmos. Sci, 36 , 2450–2466.

    • Search Google Scholar
    • Export Citation

  • Buzzi, A., and E. Tosi, 1989: Statistical behavior of transient eddies near mountains and implications for theories of lee cyclogenesis. J. Atmos. Sci, 46 , 1233–1249.

    • Search Google Scholar
    • Export Citation

  • Carrera, M. L., J. R. Gyakum, and D-L. Zhang, 1999: A numerical case study of secondary marine cyclogenesis sensitivity to initial error and varying physical processes. Mon. Wea. Rev, 127 , 641–660.

    • Search Google Scholar
    • Export Citation

  • Chang, E. K. M., 1993: Downstream development of baroclinic waves as inferred from regression analysis. J. Atmos. Sci, 50 , 2038–2053.

  • Chang, E. K. M., 1999: Characteristics of wave packets in the upper troposphere. Part II: Seasonal and hemispheric variations. J. Atmos. Sci, 56 , 1729–1747.

    • Search Google Scholar
    • Export Citation

  • Compagnucci, R. H., and M. A. Salles, 1997: Surface pressure patterns during the year over southern South America. Int. J. Climatol, 17 , 635–653.

    • Search Google Scholar
    • Export Citation

  • Davis, C. A., 1997: The modification of baroclinic waves by the Rocky Mountains. J. Atmos. Sci, 54 , 848–868.

  • Gan, M. A., and V. B. Rao, 1991: Surface cyclogenesis over South America. Mon. Wea. Rev, 119 , 1293–1302.

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

    • Search Google Scholar
    • Export Citation

  • Hoskins, B. J., I. N. James, and G. H. White, 1983: The shape, propagation, and mean-flow interaction of large-scale weather systems. J. Atmos. Sci, 40 , 1592–1612.

    • Search Google Scholar
    • Export Citation

  • Hsu, H-H., 1987: Propagation of low-level circulation features in the vicinity of mountain ranges. Mon. Wea. Rev, 115 , 1864–1892.

  • Hsu, H-H., and J. M. Wallace, 1985: Vertical structure of wintertime teleconnection patterns. J. Atmos. Sci, 42 , 1693–1710.

  • Jusem, J. C., and R. Atlas, 1991: Diagnostic evaluation of numerical model simulations using the tendency equation. Mon. Wea. Rev, 119 , 2936–2955.

    • Search Google Scholar
    • Export Citation

  • Lau, K-H., and N-C. Lau, 1990: Observed structure and propagation characteristics of tropical summertime synoptic-scale disturbances. Mon. Wea. Rev, 118 , 1888–1913.

    • Search Google Scholar
    • Export Citation

  • Lau, K-M., and P. Chan, 1985: Aspects of the 40–50 day oscillation during the northern winter as inferred from outgoing longwave radiation. Mon. Wea. Rev, 113 , 1889–1909.

    • Search Google Scholar
    • Export Citation

  • Lim, G. H., and J. M. Wallace, 1991: Structure and evolution of baroclinic waves as inferred from regression analysis. J. Atmos. Sci, 48 , 1718–1732.

    • Search Google Scholar
    • Export Citation

  • Mak, M., 1998: Influence of surface sensible heat flux on incipient marine cyclogenesis. J. Atmos. Sci, 55 , 820–834.

  • Marengo, J., 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

  • Necco, G. V., 1982a: Comportamiento de vórtices ciclónicos en el área sudamericana durante el FGGE: Ciclogénesis (Behavior of the cyclonic vortices in the South American region during FGGE: Cyclogenesis). Meteorologica, 13 , 7–20.

    • Search Google Scholar
    • Export Citation

  • Necco, G. V., 1982b: Comportamiento de vórtices ciclónicos en el área sudamericana durante el FGGE: Trayectorias y desarrollos (Behavior of the cyclonic vortices in the South American region during FGGE: Tracks and developments). Meteorologica, 13 , 21–34.

    • Search Google Scholar
    • Export Citation

  • Peterson, R. G., and L. Stramma, 1991: Upper-level circulation in the South Atlantic Ocean. Progress in Oceanography, Vol. 26, Pergamon Press, 1–73.

    • Search Google Scholar
    • Export Citation

  • Saraiva, J. M. B., and P. L. Silva Dias, 1997: A case study of intense cyclogenesis off the southern coast of Brazil: Impact of SST, stratiform and deep convection. Preprints, Fifth Conf. on Southern Hemisphere Meteorology and Oceanography, Pretoria, South Africa, Amer. Meteor. Soc., 368–369.

    • Search Google Scholar
    • Export Citation

  • Seluchi, M. E., and A. C. Saulo, 1997: Simulación de 10 episodios de ciclogénesis costeras sobre Sudamérica utilizando un modelo regional (Simulation of 10 episodes of coastal cyclogenesis over South America using a regional model). Meteorologica, 22 , 49–66.

    • Search Google Scholar
    • Export Citation

  • Seluchi, M. E., and A. C. Saulo, 1998: Possible mechanisms yielding an explosive coastal cyclogenesis over South America: Experiments using a limited area model. Aust. Meteor. Mag, 47 , 309–320.

    • 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

  • Simmonds, I., and K. Keay, 2000: Mean Southern Hemisphere extratropical cyclone behavior in the 40-Year NCEP–NCAR Reanalysis. J. Climate, 13 , 873–885.

    • Search Google Scholar
    • Export Citation

  • Taljaard, J. J., 1972: Synoptic meteorology in the Southern Hemisphere. Meteorology of the Southern Hemisphere, Meteor. Monogr., No. 35, Amer. Meteor. Soc., 139–213.

    • Search Google Scholar
    • Export Citation

  • Trenberth, K. E., 1981: Observed Southern Hemisphere eddy statistics at 500 mb: Frequency and spatial dependence. J. Atmos. Sci, 38 , 2585–2605.

    • Search Google Scholar
    • Export Citation

  • Uccellini, L. W., 1990: Processes contributing to the rapid development of extratropical cyclones. Extratropical Cyclones: The Erik Palmén Memorial Volume, C. W. Newton and E. O. Holopainen, Eds., Amer. Meteor. Soc., 81–105.

    • 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.

  • Vigliarolo, P. K., C. S. Vera, and S. Diaz, 2001: Southern Hemisphere winter ozone fluctuations. Quart. J. Roy. Meteor. Soc, 127 , 559–578.

    • Search Google Scholar
    • Export Citation

  • Walsh, C. H., J. E. Peak, W. F. Calland, and W. A. Cook, 1988: Diagnostic study of explosive cyclogenesis during FGGE. Mon. Wea. Rev, 116 , 431–451.

    • Search Google Scholar
    • Export Citation

  • Weare, B. C., and J. S. Nasstrom, 1982: Examples of extended empirical orthogonal function analyses. Mon. Wea. Rev, 110 , 481–485.

  • Xie, P., and P. A. Arkin, 1997: Global precipitation: A 17-year monthly analysis based on gauge observations, satellite estimates, and numerical model outputs. Bull. Amer. Meteor. Soc, 78 , 2539–2558.

    • Search Google Scholar
    • Export Citation

  • Yu, J-Y., and D. L. Hartmann, 1995: Orographic influences on the distribution and generation of atmospheric variability in a GCM. J. Atmos. Sci, 52 , 2428–2443.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 1572 833 70
PDF Downloads 521 134 5