• Bettge, W., , and D. P. Baumhefner, 1980: A method to decompose the spatial characteristics of meteorological variables within a limited domain. Mon. Wea. Rev, 108 , 843854.

    • Search Google Scholar
    • Export Citation
  • Colton, D. E., 1973: Barotropic scale interactions in the tropical upper troposphere during the northern summer. J. Atmos. Sci, 30 , 12871302.

    • Search Google Scholar
    • Export Citation
  • Drazin, P. G., , and W. H. Reid, 1981: Hydrodynamic Stability. Cambridge University Press, 525 pp.

  • Ferreira, R. N., , and W. H. Schubert, 1999: The role of tropical cyclones in the formation of tropical upper-tropospheric troughs. J Atmos. Sci, 56 , 28912907.

    • Search Google Scholar
    • Export Citation
  • Holloway, J. L., 1958: Smoothing and filtering of time series and space fields. Advances in Geophysics, Vol. 4, Academic Press, 351–389.

    • Search Google Scholar
    • Export Citation
  • Holopainen, E., , and P. Nurmi, 1979: Acceleration of a diffluent jet stream by horizontal subgrid scale processes—An example of a scale interaction study employing a horizontal filtering technique. Tellus, 31 , 246253.

    • Search Google Scholar
    • Export Citation
  • Holton, J. R., 1992: An Introduction to Dynamic Meteorology. 3d ed. Academic Press, 507 pp.

  • James, I. N., 1994: Introduction to Circulating Atmospheres. Atmospheric and Space Science Series, Cambridge University Press, 422 pp.

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

  • Kayano, M. T., , N. J. Ferreira, , and M. C. V. Ramírez, 1997: Summer circulation patterns related to the upper tropospheric vortices over the tropical South Atlantic. Meteor. Atmos. Phys, 64 , 203213.

    • Search Google Scholar
    • Export Citation
  • Kousky, V. E., , and M. A. Gan, 1981: Upper tropospheric cyclonic vortices in tropical south Atlantic. Tellus, 33 , 538550.

  • Kuo, H. L., 1949: Dynamical instability of two-dimensional nondivergent flow in a barotropic atmosphere. J. Meteor, 6 , 18401860.

  • Kurihara, Y., , M. A. Bender, , and R. J. Ross, 1993: An initialization scheme of hurricane models by vortex specification. Mon. Wea. Rev, 121 , 20302045.

    • Search Google Scholar
    • Export Citation
  • Lenters, J. D., , and K. H. Cook, 1997: On the origin of the Bolivian high and related circulation features of the South America climate. J. Atmos. Sci, 54 , 656677.

    • Search Google Scholar
    • Export Citation
  • Mishra, S. K., 1993: Nonlinear barotropic instability of upper-tropospheric tropical easterly jet on the sphere. J. Atmos. Sci, 50 , 35413552.

    • Search Google Scholar
    • Export Citation
  • ——, Subrahmanayam, D., , and M. K. Tandon, 1981: Divergent barotropic instability of the tropical asymmetric easterly jet. J. Atmos. Sci, 38 , 21642171.

    • Search Google Scholar
    • Export Citation
  • ——, Patwardhan, M. D., , and L. George, 1985: A primitive equation barotropic instability study of the monsoon onset vortex, 1979. Quart. J. Roy. Meteor. Soc, 111 , 427444.

    • Search Google Scholar
    • Export Citation
  • Newell, R. E., , J. W. Kidson, , D. G. Vincent, , and G. J. Boer, 1972: The General Circulation of the Tropical Atmosphere and Interactions with Extratropical Latitudes. Vol I. Massachusets Institute of Technology Press, 258 pp.

    • Search Google Scholar
    • Export Citation
  • Ramírez, M. C. V., , T. Kayano, , and N. J. Ferreira, 1999: Statistical analysis of upper tropospheric vortices in the vicinity of northeast Brazil during the 1980–1989 period. Atmosfera, 12 , 7588.

    • Search Google Scholar
    • Export Citation
  • Rao, V. B., , and J. P. Bonatti, 1987: On the origin of upper tropospheric cyclonic vortices in the South Atlantic Ocean and adjoining Brazil during the summer. Meteor. Atmos. Phys, 37 , 1116.

    • Search Google Scholar
    • Export Citation
  • Shapiro, R., 1970: Smoothing, filtering, and boundary effect. Rev. Geophys. Space Phys, 8 , 359389.

  • Silva Dias, P. L., , W. H. Schubert, , and M. DeMaria, 1983: Large-scale response of the tropical atmosphere to transient convection. J. Atmos. Sci, 40 , 26892707.

    • Search Google Scholar
    • Export Citation
  • Virji, H., 1981: A preliminary study of summer time tropospheric circulation patterns over South America estimated from cloud winds. Mon. Wea. Rev, 109 , 599610.

    • Search Google Scholar
    • Export Citation
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Structure and Evolution of the Large-Scale Flow and an Embedded Upper-Tropospheric Cyclonic Vortex over Northeast Brazil

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  • 1 Instituo Nacional de Pesquisas Espaciais, Sao Jose dos Campos, Sao Paulo, Brazil
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Abstract

Horizontal structure and evolution of large-scale flow and an embedded synoptic-scale cyclonic vortex over northeast Brazil as separate systems and dynamical interaction between them are studied at 200 hPa. A quasi-stationary cyclonic vortex with its average position at 10°S and 35°W that formed and remained active during 5–10 January 1993 is selected for the investigation. The evolution of large-scale flow in the prevortex period 1–4 January is also explored. An efficient and effective scale separation technique is developed and used to separate the large-scale flow and embedded synoptic-scale vortex.

It is shown that a strong positive shear zone developed in the latitude domain 17.5°–7.5°S, within the South Atlantic trough region before the vortex formation. The shear zone has a characteristic meridional (zonal) scale of 1000 km (3000 km) and satisfies strongly the necessary condition for barotropic instability. It is identified that the development of a strong shear zone is associated with the intensification of a Bolivian anticyclone and associated ridge and their eastward shift, and intensification of the South Atlantic trough, east–west orientation of the Atlantic trough, and the presence of a transient trough over the equatorial Atlantic Ocean.

The average structure of vortex including zonal and meridional characteristic scales is computed from the synoptic bandpass flow. The vortex is identified as a nonlinear wave packet with an average zonal wavelength of 2750 km and it is confined to a latitude belt of about 17.5°. The vortex shows a strong westward tilt with latitude; the convergence zone is located to its southwest and it is a weak cold cored system. Maximum cyclonic vorticity of the vortex is −3.24 × 10−5 s−1, which is comparable to the value for embedding flow.

The momentum transports due to the vortex, large-scale eddy, and the vortex–large-scale eddy interaction are computed. It is found that the vortex and vortex–large-scale eddy westerly momentum transports are southward, down the gradient of embedding zonal flow, and their divergence (convergence) is located over the latitudes of large scale westerlies (easterlies). The sensible heat transports are weak. It is noted that the vortex–large-scale flow interaction leads to the weakening of the shear zone and restoration of the large circulation features to their January 1993 mean configuration, which have undergone significant deviation during the prevortex period. The signature of vortex–large-scale interaction is also seen in the evolution of dynamical parameters qy and n2 (square of refractive index parameter).

Corresponding author address: Dr. S. K. Mishra, 163/24 Mausam Vihar, D. P. Road, Aundh, Pune-411 007, India.Email: skmishra@mailmetoday.com

Abstract

Horizontal structure and evolution of large-scale flow and an embedded synoptic-scale cyclonic vortex over northeast Brazil as separate systems and dynamical interaction between them are studied at 200 hPa. A quasi-stationary cyclonic vortex with its average position at 10°S and 35°W that formed and remained active during 5–10 January 1993 is selected for the investigation. The evolution of large-scale flow in the prevortex period 1–4 January is also explored. An efficient and effective scale separation technique is developed and used to separate the large-scale flow and embedded synoptic-scale vortex.

It is shown that a strong positive shear zone developed in the latitude domain 17.5°–7.5°S, within the South Atlantic trough region before the vortex formation. The shear zone has a characteristic meridional (zonal) scale of 1000 km (3000 km) and satisfies strongly the necessary condition for barotropic instability. It is identified that the development of a strong shear zone is associated with the intensification of a Bolivian anticyclone and associated ridge and their eastward shift, and intensification of the South Atlantic trough, east–west orientation of the Atlantic trough, and the presence of a transient trough over the equatorial Atlantic Ocean.

The average structure of vortex including zonal and meridional characteristic scales is computed from the synoptic bandpass flow. The vortex is identified as a nonlinear wave packet with an average zonal wavelength of 2750 km and it is confined to a latitude belt of about 17.5°. The vortex shows a strong westward tilt with latitude; the convergence zone is located to its southwest and it is a weak cold cored system. Maximum cyclonic vorticity of the vortex is −3.24 × 10−5 s−1, which is comparable to the value for embedding flow.

The momentum transports due to the vortex, large-scale eddy, and the vortex–large-scale eddy interaction are computed. It is found that the vortex and vortex–large-scale eddy westerly momentum transports are southward, down the gradient of embedding zonal flow, and their divergence (convergence) is located over the latitudes of large scale westerlies (easterlies). The sensible heat transports are weak. It is noted that the vortex–large-scale flow interaction leads to the weakening of the shear zone and restoration of the large circulation features to their January 1993 mean configuration, which have undergone significant deviation during the prevortex period. The signature of vortex–large-scale interaction is also seen in the evolution of dynamical parameters qy and n2 (square of refractive index parameter).

Corresponding author address: Dr. S. K. Mishra, 163/24 Mausam Vihar, D. P. Road, Aundh, Pune-411 007, India.Email: skmishra@mailmetoday.com

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