• Edmon, H. J., Jr., B. J. Hoskins, and M. E. McIntyre, 1980: Eliassen–Palm cross sections for the troposphere. J. Atmos. Sci.,37, 2600–2616; Corrigendum, 38, 1115.

  • Hartmann, D. L., 1995: A PV view of zonal flow vacillation. J. Atmos. Sci.,52, 2561–2576.

  • Haynes, P. H., 1988: Forced, dissipative generalizations of finite- amplitude wave-activity conservation relations for zonal and nonzonal basic flows. J. Atmos. Sci.,45, 2352–2362.

  • Hoskins, B. J., and D. J. Karoly, 1981: The steady-state linear response of a spherical atmosphere to thermal and orographic forcing. J. Atmos. Sci.,38, 1179–1196.

  • ——, M. E. McIntyre, and A. W. Robertson, 1985: On the use and significance of isentropic potential-vorticity maps. Quart. J. Roy. Meteor. Soc.,111, 877–946.

  • James, I. N., 1987: Suppression of baroclinic instability in horizontally sheared flows. J. Atmos. Sci.,44, 3710–3720.

  • ——, and J. P. Dodd, 1996: A mechanism for the low-frequency variability of the mid-latitude troposphere. Quart. J. Roy. Meteor. Soc.,122, 1197–1210.

  • Karoly, D., and B. J. Hoskins, 1982: Three-dimensional propagation of planetary waves. J. Meteor. Soc. Japan,60, 109–123.

  • Lorenz, E. N., 1964: The problem of deducing the climate from the governing equations. Tellus,16, 21–31.

  • ——, 1967: The Nature and Theory of the General Circulation of the Atmosphere. World Meteorological Organization, 161 pp.

  • Magnusdottir, G., and P. H. Haynes, 1996: Wave activity diagnostics applied to baroclinic wave life cycles. J. Atmos. Sci.,53, 2317–2353.

  • Matsuno, T., 1970: Vertical propagation of stationary planetary waves in the winter Northern Hemisphere. J. Atmos. Sci.,27, 871–883.

  • Simmons, A. J., and B. J. Hoskins, 1980: Barotropic influences on the growth and decay of nonlinear baroclinic waves. J. Atmos. Sci.,37, 1679–1684.

  • Thorncroft, C. D., B. J. Hoskins, and M. E. McIntyre, 1993: Two paradigms of baroclinic life-cycle behaviour. Quart. J. Roy. Meteor. Soc.,119, 17–55.

  • Yu, J.-Y., and D. L. Hartmann, 1993: Zonal flow vacillation and eddy forcing in a simple GCM of the atmosphere. J. Atmos. Sci.,50, 3244–3259.

  • Zuercher, P., 1996: Bimodal response of baroclinic wave lifecycles to changes in horizontal, barotropic shear. M.S. thesis, Dept. of Atmospheric Sciences, University of Washington, 114 pp. [Available from Resource Sharing, Suzzallo and Allen Library, Box 352900, University of Washington, Seattle, WA 92195.].

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 109 109 81
PDF Downloads 24 24 3

Response of Baroclinic Life Cycles to Barotropic Shear

View More View Less
  • 1 Department of Atmospheric Sciences, University of Washington, Seattle, Washington
© Get Permissions
Restricted access

Abstract

Cyclonic barotropic shear of incrementally increasing magnitude is imposed on an idealized midlatitude jet, and the life cycles of baroclinically unstable wavenumber 6 perturbations growing on these jets are studied. When the barotropic shear parameter passes a critical value, the life cycle makes an abrupt transition from anticyclonic to cyclonic behavior. The abrupt transition in behavior is most evident in the barotropic decay of eddy kinetic energy, in the structure of the eddies as seen in potential vorticity maps, and in the nature of the zonal flow accelerations produced during the life cycle. It is suggested that the abrupt transition can be interpreted as arising from a positive feedback between eddy propagation and eddy-induced zonal flow accelerations. Dependences on the zonal scale of the eddy are also investigated. Wavenumber 8 exhibits cyclonic behavior, while wavenumber 4 exhibits anticyclonic behavior for all values of cyclonic shear considered. This dependence on zonal scale is consistent with predictions of linear WKB wave propagation theory. The sharpness of the transition in life cycle behavior has implications for medium-range predictability and for the generation of low- frequency variability in the atmosphere.

Corresponding author address: Dr. Dennis L. Hartmann, Department of Atmospheric Sciences, Box 351640, University of Washington, Seattle, WA 98195.

Email: dennis@atmos.washington.edu

Abstract

Cyclonic barotropic shear of incrementally increasing magnitude is imposed on an idealized midlatitude jet, and the life cycles of baroclinically unstable wavenumber 6 perturbations growing on these jets are studied. When the barotropic shear parameter passes a critical value, the life cycle makes an abrupt transition from anticyclonic to cyclonic behavior. The abrupt transition in behavior is most evident in the barotropic decay of eddy kinetic energy, in the structure of the eddies as seen in potential vorticity maps, and in the nature of the zonal flow accelerations produced during the life cycle. It is suggested that the abrupt transition can be interpreted as arising from a positive feedback between eddy propagation and eddy-induced zonal flow accelerations. Dependences on the zonal scale of the eddy are also investigated. Wavenumber 8 exhibits cyclonic behavior, while wavenumber 4 exhibits anticyclonic behavior for all values of cyclonic shear considered. This dependence on zonal scale is consistent with predictions of linear WKB wave propagation theory. The sharpness of the transition in life cycle behavior has implications for medium-range predictability and for the generation of low- frequency variability in the atmosphere.

Corresponding author address: Dr. Dennis L. Hartmann, Department of Atmospheric Sciences, Box 351640, University of Washington, Seattle, WA 98195.

Email: dennis@atmos.washington.edu

Save