Editorial Type:
Article
Article Type:
Research Article

Precipitation and Water Vapor Transport in the Southern Hemisphere with Emphasis on the South American Region

Josefina Moraes Arraut Centro de Ciências do Sistema Terrestre, Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Brazil

Search for other papers by Josefina Moraes Arraut in
Current site
Google Scholar
PubMed Close
and
Prakki Satyamurty Instituto Nacional de Pesquisas Espaciais, São José dos Campos, and Instituto Nacional de Pesquisas Amazônicas, Manaus, Brazil

Search for other papers by Prakki Satyamurty in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Sep 2009
DOI:
https://doi.org/10.1175/2009JAMC2030.1
Page(s):
1902–1912
Restricted access

Abstract

December–March climatologies of precipitation and vertically integrated water vapor transport were analyzed and compared to find the main paths by which moisture is fed to high-rainfall regions in the Southern Hemisphere in this season. The southern tropics (20°S–0°) exhibit high rainfall and receive ample moisture from the northern trades, except in the eastern Pacific and the Atlantic Oceans. This interhemispheric flow is particularly important for Amazonian rainfall, establishing the North Atlantic as the main source of moisture for the forest during its main rainy season. In the subtropics the rainfall distribution is very heterogeneous. The meridional average of precipitation between 35° and 25°S is well modulated by the meridional water vapor transport through the 25°S latitude circle, being greater where this transport is from the north and smaller where it is from the south. In South America, to the east of the Andes, the moisture that fuels precipitation between 20° and 30°S comes from both the tropical South and North Atlantic Oceans whereas between 30° and 40°S it comes mostly from the North Atlantic after passing over the Amazonian rain forest. The meridional transport (across 25°S) curve exhibits a double peak over South America and the adjacent Atlantic, which is closely reproduced in the mean rainfall curve. This corresponds to two local maxima in the two-dimensional field of meridional transport: the moisture corridor from Amazonia into the continental subtropics and the moisture flow coming from the southern tropical Atlantic into the subtropical portion of the South Atlantic convergence zone. These two narrow pathways of intense moisture flow could be suitably called “aerial rivers.” Their longitudinal positions are well defined. The yearly deviations from climatology for moisture flow and rainfall correlate well (0.75) for the continental peak but not for the oceanic peak (0.23). The structure of two maxima is produced by the effect of transients in the time scale of days.

Corresponding author address: Josefina Moraes Arraut, Instituto Nacional de Pesquisas Espaciais - prédio IGBP, Ave. dos Astronautas 10758, São José dos Campos, SP 12227-010, Brazil. Email: josefina.arraut@cptec.inpe.br

Abstract

December–March climatologies of precipitation and vertically integrated water vapor transport were analyzed and compared to find the main paths by which moisture is fed to high-rainfall regions in the Southern Hemisphere in this season. The southern tropics (20°S–0°) exhibit high rainfall and receive ample moisture from the northern trades, except in the eastern Pacific and the Atlantic Oceans. This interhemispheric flow is particularly important for Amazonian rainfall, establishing the North Atlantic as the main source of moisture for the forest during its main rainy season. In the subtropics the rainfall distribution is very heterogeneous. The meridional average of precipitation between 35° and 25°S is well modulated by the meridional water vapor transport through the 25°S latitude circle, being greater where this transport is from the north and smaller where it is from the south. In South America, to the east of the Andes, the moisture that fuels precipitation between 20° and 30°S comes from both the tropical South and North Atlantic Oceans whereas between 30° and 40°S it comes mostly from the North Atlantic after passing over the Amazonian rain forest. The meridional transport (across 25°S) curve exhibits a double peak over South America and the adjacent Atlantic, which is closely reproduced in the mean rainfall curve. This corresponds to two local maxima in the two-dimensional field of meridional transport: the moisture corridor from Amazonia into the continental subtropics and the moisture flow coming from the southern tropical Atlantic into the subtropical portion of the South Atlantic convergence zone. These two narrow pathways of intense moisture flow could be suitably called “aerial rivers.” Their longitudinal positions are well defined. The yearly deviations from climatology for moisture flow and rainfall correlate well (0.75) for the continental peak but not for the oceanic peak (0.23). The structure of two maxima is produced by the effect of transients in the time scale of days.

Corresponding author address: Josefina Moraes Arraut, Instituto Nacional de Pesquisas Espaciais - prédio IGBP, Ave. dos Astronautas 10758, São José dos Campos, SP 12227-010, Brazil. Email: josefina.arraut@cptec.inpe.br

Save
Cover Journal of Applied Meteorology and Climatology
Journal of Applied Meteorology and Climatology

  • Arraut, J. M., 2007: Fronts and frontogenesis during summer: Geometrical and dynamical aspects and the influence over rainfall on the South American subtropics (in Portuguese). Ph.D. thesis. [Available online at http://mtc-m17.sid.inpe.br/col/sid.inpe.br/mtc-m17%4080/2007/12.19.10.53/doc/publicacao.pdf].

  • D’Abreton, P. C., and P. Tyson, 1995: Divergent and non-divergent water vapour transport over southern Africa during wet and dry conditions. Meteor. Atmos. Phys., 55 , 47–59.

    • 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 , 2713–2733.

    • Search Google Scholar
    • Export Citation

  • Huffman, G. J., R. Adler, M. Morrissey, D. T. Bolvin, S. Curtis, R. Joyce, B. McGavock, and J. Susskind, 2001: Global precipitation at one-degree daily resolution from multisatellite observations. J. Hydrometeor., 2 , 36–50.

    • Search Google Scholar
    • Export Citation

  • 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 , 813–835.

    • Search Google Scholar
    • Export Citation

  • Kodama, Y-M., 1993: Large-scale common features of subtropical precipitation zones (the Baiu frontal zone, the SPCZ and the SACZ) Part II: Conditions of the circulation for generating STCZs. J. Meteor. Soc. Japan, 71 , 581–610.

    • 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. J. Geophys. Res., 26 , 1409–1412.

    • Search Google Scholar
    • Export Citation

  • Nogués-Paegle, J., and K. Mo, 1997: Alternating wet and dry conditions over South America during summer. Mon. Wea. Rev., 125 , 279–291.

    • Search Google Scholar
    • Export Citation

  • Salio, P., M. Nicolini, and 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

  • Salio, P., M. Nicolini, and E. Zipser, 2007: Mesoscale convective systems over southeastern South America and their relationship with the South American low-level jet. Mon. Wea. Rev., 135 , 1290–1310.

    • Search Google Scholar
    • Export Citation

  • Satyamurty, P., C. A. Nobre, and P. L. Silva Dias, 1998: Tropics: South America. Meteorology of the Southern Hemisphere, Meteor. Monogr., No. 49, Amer. Meteor. Soc., 119–140.

    • Search Google Scholar
    • Export Citation

  • Saulo, C., M. E. Seluchi, and M. Nicolini, 2004: A case study of a Chaco low-level jet event. Mon. Wea. Rev., 132 , 2669–2683.

  • Saulo, C., J. Ruiz, and Y. G. Skabar, 2007: Synergism between the low-level jet and organized convection in its exit region. Mon. Wea. Rev., 135 , 1310–1326.

    • Search Google Scholar
    • Export Citation

  • Seluchi, M. E., and J. 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., C. Saulo, M. Nicolini, and P. Satyamurty, 2003: The northwestern Argentinean low: A study of two typical events. Mon. Wea. Rev., 131 , 2361–2378.

    • Search Google Scholar
    • Export Citation

  • Siqueira, J. R., and L. A. T. Machado, 2004: Influence of the frontal systems on the day-to-day convection variability over South America. J. Climate, 17 , 1754–1766.

    • Search Google Scholar
    • Export Citation

  • Uccellini, L. W., and D. R. Johnson, 1979: The coupling of upper and lower tropospheric jet streaks and implications for the development of severe convective systems. Mon. Wea. Rev., 107 , 662–703.

    • Search Google Scholar
    • Export Citation

  • Vera, C., and Coauthors, 2006: Toward a unified view of the American monsoon systems. J. Climate, 19 , 4977–5000.

  • Virji, H., 1981: A preliminary study of summertime tropospheric circulation patterns over South America estimated from cloud winds. Mon. Wea. Rev., 109 , 599–610.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 584 256 13
PDF Downloads 442 145 9