Characteristics of Wave Packets in the Upper Troposphere. Part I: Northern Hemisphere Winter

Edmund K. M. Chang Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Cambridge, Massachusetts

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Daniel B. Yu Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Cambridge, Massachusetts

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Abstract

Gridded data produced by the ECMWF reanalysis project have been analyzed to document the properties of wave packets in the Northern Hemisphere winter midlatitude upper troposphere. Based on results from earlier investigations, 300-hPa meridional wind variations were chosen for analysis. Wave packet envelopes were also defined by performing complex demodulation on the wind data. The properties of the wave packets are mainly illustrated using time-lagged one-point correlation maps performed both on υ′ and wave packet envelopes.

The results show that, over most regions in the Northern Hemisphere winter, with the exception of the deep Tropics and near the Aleutian low, medium-scale waves (dominant wavenumber 5–8) exhibit the characteristics of downstream development and occur within wave trains that propagate with eastward group velocities much faster than the phase speeds of individual phases of the waves. Their group velocity is highly correlated with the local time mean 200–400-hPa wind, while the phase speed is well correlated with the 500–700-hPa flow.

A wave coherence index has been defined to show the geographical variations in the downstream development tendency of wave propagation. The results show that wave packets are most coherent along a band that extends from North Africa into southern Asia, toward the Pacific storm track, across North America, then over the central North Atlantic back toward North Africa. The maximum coherence occurs over southern Asia. This band can be regarded as the waveguide for upper-tropospheric wave packets in the Northern Hemisphere winter. Over this band, wave packets generally stay coherent significantly longer than individual troughs and ridges. There is also a secondary waveguide across Russia toward the Pacific, acting as a second source of waves that propagate across the Pacific storm track. Away from the primary waveguide, while wave packet coherence is less, the waves still show the characteristics of downstream development.

* Additional affiliation: Physics Department, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Corresponding author address: Dr. Edmund K. Chang, Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Room 54-1614, Cambridge, MA 02139.

Abstract

Gridded data produced by the ECMWF reanalysis project have been analyzed to document the properties of wave packets in the Northern Hemisphere winter midlatitude upper troposphere. Based on results from earlier investigations, 300-hPa meridional wind variations were chosen for analysis. Wave packet envelopes were also defined by performing complex demodulation on the wind data. The properties of the wave packets are mainly illustrated using time-lagged one-point correlation maps performed both on υ′ and wave packet envelopes.

The results show that, over most regions in the Northern Hemisphere winter, with the exception of the deep Tropics and near the Aleutian low, medium-scale waves (dominant wavenumber 5–8) exhibit the characteristics of downstream development and occur within wave trains that propagate with eastward group velocities much faster than the phase speeds of individual phases of the waves. Their group velocity is highly correlated with the local time mean 200–400-hPa wind, while the phase speed is well correlated with the 500–700-hPa flow.

A wave coherence index has been defined to show the geographical variations in the downstream development tendency of wave propagation. The results show that wave packets are most coherent along a band that extends from North Africa into southern Asia, toward the Pacific storm track, across North America, then over the central North Atlantic back toward North Africa. The maximum coherence occurs over southern Asia. This band can be regarded as the waveguide for upper-tropospheric wave packets in the Northern Hemisphere winter. Over this band, wave packets generally stay coherent significantly longer than individual troughs and ridges. There is also a secondary waveguide across Russia toward the Pacific, acting as a second source of waves that propagate across the Pacific storm track. Away from the primary waveguide, while wave packet coherence is less, the waves still show the characteristics of downstream development.

* Additional affiliation: Physics Department, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Corresponding author address: Dr. Edmund K. Chang, Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Room 54-1614, Cambridge, MA 02139.

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  • 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.

  • Blackmon, M. L., 1976: A climatological spectral study of the 500-mb geopotential height of the Northern Hemisphere. J. Atmos. Sci.,33, 1607–1623.

  • ——, J. M. Wallace, N.-C. Lau, and S. L. Mullen, 1977: An observational study of the Northern Hemisphere wintertime circulation. J. Atmos. Sci.,34, 1040–1053.

  • ——, Y. H. Lee, and J. M. Wallace, 1984a: Horizontal structure of 500-mb height fluctuations with long, intermediate, and short time scales. J. Atmos. Sci.,41, 961–979.

  • ——, ——, ——, and H. H. Hsu, 1984b: Time variation of 500-mb height fluctuations with long, intermediate, and short timescales as deduced from lag-correlation statistics. J. Atmos. Sci.,41, 981–991.

  • Bloomfield, P., 1976: Fourier Analysis of Time Series: An Introduction. Wiley-Interscience, 258 pp.

  • Briggs, R. J., 1964: Electron-Stream Interaction with Plasmas. The MIT Press.

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

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

  • ——, and I. Orlanski, 1993: On the dynamics of a storm track. J. Atmos. Sci.,50, 999–1015.

  • ——, and ——, 1994: On energy flux and group velocity of waves in baroclinic flows. J. Atmos. Sci.,51, 3823–3828.

  • Cressman, G. P., 1948: On the forecasting of long waves in the upper westerlies. J. Meteor.,5, 44–57.

  • 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, 1595–1612.

  • ——, 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.

  • Hovmöller, E., 1949: The trough-and-ridge diagram. Tellus,1, 62–66.

  • Joung, C. H., and M. H. Hitchman, 1982: On the role of successive downstream development in East Asian polar air outbreaks. Mon. Wea. Rev.,110, 1224–1237.

  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc.,77, 437–471.

  • Kao, S. K., and L. L. Wendell, 1970: The kinetic energy of the large-scale atmospheric motion in wavenumber-frequency space: I. Northern Hemisphere. J. Atmos. Sci.,27, 359–375.

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

  • 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.

  • Lau, N.-C., 1978: On the three-dimensional structure of the observed transient eddy statistics of the Northern Hemisphere wintertime circulation. J. Atmos. Sci.,35, 1900–1923.

  • Lee, S., and I. M. Held, 1993: Baroclinic wave packets in models and observations. J. Atmos. Sci.,50, 1413–1428.

  • ——, and S. B. Feldstein, 1996: Two types of wave breaking in an aqua-planet GCM. J. Atmos. Sci.,53, 842–857.

  • 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.

  • Livezey, R. E., and W. Y. Chen, 1983: Statistical field significance and its determination by Monte Carlo techniques. Mon. Wea. Rev.,111, 46–59.

  • Merkine, L. O., 1977: Convective and absolute instability of baroclinic eddies. Geophys. Astrophys. Fluid Dyn.,9, 129–157.

  • Namias, J., and P. F. Clapp, 1944: Studies of the motion and development of long waves in the westerlies. J. Meteor.,1, 57–77.

  • Nielsen-Gammon, J. W., 1995: Dynamical conceptual models of upper-level mobile trough formation: Comparison and application. Tellus,47A, 705–721.

  • ——, and R. J. Lefevre, 1996: Piecewise tendency diagnosis of dynamical processes governing the development of an upper-tropospheric mobile trough. J. Atmos. Sci.,53, 3120–3142.

  • Orlanski, I., and E. K. M. Chang, 1993: Ageostrophic geopotential fluxes in downstream and upstream development of baroclinic waves. J. Atmos. Sci.,50, 212–225.

  • ——, and J. P. Sheldon, 1995: Stages in the energetics of baroclinic systems. Tellus,47A, 605–628.

  • Pierrehumbert, R. T., 1984: Local and global baroclinic instability of zonally varying flow. J. Atmos. Sci.,41, 2141–2162.

  • Plumb, R. A., 1986: Three-dimensional propagation of transient quasi-geostrophic eddies and its relationship with the eddy forcing of the time–mean flow. J. Atmos. Sci.,43, 1657–1678.

  • Simmons, A. J., and B. J. Hoskins, 1978: The life cycles of some nonlinear baroclinic waves. J. Atmos. Sci.,35, 414–432.

  • ——, and ——, 1979: The downstream and upstream development of unstable baroclinic waves. J. Atmos. Sci.,36, 1239–1254.

  • Swanson, K., and R. T. Pierrehumbert, 1994: Nonlinear wave packet evolution on a baroclinically unstable jet. J. Atmos. Sci.,51, 384–394.

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

  • Wallace, J. M., G. H. Lim, and M. L. Blackmon, 1988: Relationship between cyclone tracks, anti-cyclone tracks, and baroclinic waveguides. J. Atmos. Sci.,45, 439–462.

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