Meteorology and Atmospheric Physics

, Volume 38, Issue 1–2, pp 22–33 | Cite as

The structure and characteristics of African easterly wave disturbances as determined from the ECMWF operational analysis/forecast system

  • R. J. Reed
  • E. Klinker
  • A. Hollingsworth


Gridded data from the ECMWF archives are analyzed spectrally in order to determine the structure and characteristics of the African wave disturbances observed during August–September 1985. Major findings are:
  1. (1)

    The most prominent peaks in the 850 mb meridional wind spectra occurred at periods of 3–5 days. Co-spectrum analysis revealed that the 3–5-day oscillations were produced by waves of approximately 2500 km wavelength that travelled westward at speeds of about 8 m s−1.

  2. (2)

    Patterns of vorticity variance in the 3–5-day frequency band indicated that the waves originated primarily in two regions, one centered near 10°E and 22°N and the other centered near 10°E and 12°N, and that the storm tracks emanating from these regions merged into a single track, located between 15° and 20°N, over the Atlantic.

  3. (3)

    The energetics of the waves, inferred from covariance patterns of temperature, vertical velocity and meridional and zonal winds, indicated that the waves formed as a result of the joint baroclinic/barotropic instability of the African Easterly Jet. There was evidence that wave-CISK enhanced the growth of the waves that followed the southerly storm track.


The findings are in good agreement with those found in previous studies. It is concluded that the ECMWF operational analysis/forecast system gives a realistic portrayal of African easterly waves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Albignat, J. P., Reed, R. J., 1980: The origin of African wave disturbances during Phase III of GATE.Mon. Wea. Rev.,108, 1827–1839.Google Scholar
  2. Burpee, R. W., 1972: The origin and structure of easterly waves in the lower troposphere of North Africa.J. Atmos. Sci.,29, 77–90.Google Scholar
  3. Burpee, R. W., 1975: Some features of synoptic-scale waves based on compositing analysis of GATE data.Mon. Wea. Rev.,103, 921–925.Google Scholar
  4. Carlson, T. N., 1969: Some remarks on African disturbances and their progress over the tropical Atlantic.Mon. Wea. Rev. 97, 716–726.Google Scholar
  5. Carlson, T. N., Prospero, J. M., 1972: The large-scale movement of Saharan air outbreaks over the Northern Equatorial Atlantic.J. Appl. Meteor.,11, 283–297.Google Scholar
  6. Estoque, M. A., Shukla, J., Jing, J. C., 1983: African wave disturbances in a general circulation model.Tellus,35 A, 287–295.Google Scholar
  7. Jaraud, M., Simmons, A. J., Kanamitsu, M., 1985: Development of the high resolution model. ECMWF Tech. Memo. 107. Reading, U.K., 61 pp.Google Scholar
  8. Klinker, E., Capaldo, M., 1986: Systematic errors in the baroclinic waves of the ECMWF mode.Tellus,38 A, 215–235.Google Scholar
  9. Krishnamurti, T. N., Pasch, R. J., Ardanuy, P., 1980: Prediction of African waves and specification of squall lines.Tellus,32, 215–231.Google Scholar
  10. Lindzen, R. S., 1974: Wave-CISK in the tropics.J. Atmos. Sci.,31, 156–179.Google Scholar
  11. Mass, C., 1979: A linear primitive equation model of African wave disturbances.J. Atmos. Sci.,36, 2075–2092.Google Scholar
  12. Miyakoda, K., Sheldon, J., Sirutis, J., 1982: Four dimensional analysis experiment during the GATE period—Part II.J. Atmos. Sci.,39, 486–506.Google Scholar
  13. Norquist, D. C., Recker, E. E., Reed, R. J., 1977: The energetics of African wave disturbances as observed during Phase III of GATE.Mon. Wea. Rev.,105, 334–342.Google Scholar
  14. Reed, R. J., Norquist, D. C., Recker, E. E., 1977: The structure and properties of African wave disturbances as observed during Phase III of GATE.Mon. Wea. Rev.,103, 317–333.Google Scholar
  15. Reed, R. J., Hollingsworth, A., Heckley, W. E., Delsol, F., 1986: An evaluation of the performance of the ECMWF operational forecasting system in analyzing and forecasting tropical easterly wave disturbances. Part I: Synoptic Investigation. ECMWF Technical Report No. 58. Reading, U.K., 75 pp.Google Scholar
  16. Reed, R. J., Klinker, E., Hollingsworth, A., 1987: An evaluation of the performance of the ECMWF operational forecasting system in analyzing and forecasting tropical easterly wave disturbances. Part II: Spectral investigation. ECMWF Technical Report No. 60. Reading, U. K., 65 pp.Google Scholar
  17. Rennick, M. A., 1976: The generation of African waves.J. Atmos. Sci.,33, 1955–1969.Google Scholar
  18. Riehl, H., 1954:Tropical Meteorology. New York: McGraw-Hill, 392 pp.Google Scholar
  19. Rowntree, P. R., Cattle, H., 1983: The Meteorological Office GATE modelling experiment. Meteorological Office, Scientific Paper No. 40. London: Her Majesty's Stationery Office, 76 pp.Google Scholar
  20. Shaw, D., Lonnberg, P., Hollingsworth, A., Unden, P., 1987: The 1984/85 revisions of the ECMWF analysis system. To appear inQuart. J. Roy. Meteor. Soc. Google Scholar
  21. Simmons, A. J., 1977: A note on the instability of the African easterly jet.J. Atmos. Sci.,34, 1670–1674.Google Scholar
  22. Simpson, R. H., Frank, N. L., Shideler, D., Johnson, H. M., 1968: Atlantic tropical disturbances of 1967.Mon. Wea. Rev.,96, 251–259.Google Scholar
  23. Thompson, B. W., 1965:Climate of Africa. London: Oxford University Press, 132 pp.Google Scholar
  24. Thompson, R. M., Jr., Payne, S. W., Recker, E. E., Reed, R. J., 1979: Structure and properties of synoptic scale wave disturbances in the intertropical convergence zone in the eastern Atlantic.J. Atmos. Sci.,36, 53–72.Google Scholar
  25. Tiedtke, M., Heckley, W. A., Slingo, J., Simmons, A., Jarraud, M., Sommeria, G., 1987: Tropical forecasts at ECMWF: Impacts of revised physics and increased horizontal resolution. To be submitted.Google Scholar
  26. Yanai, M., Maruyama, T., Nitta, T., Hayashi, Y., 1968: Power spectra of large-scale disturbances over the tropical Pacific.J. Meteor. Soc. Japan,46, 308–323.Google Scholar

Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • R. J. Reed
    • 1
  • E. Klinker
    • 2
  • A. Hollingsworth
    • 2
  1. 1.Department of Atmospheric SciencesUniversity of WashingtonSeattleU.S.A.
  2. 2.European Centre for Medium Range Weather ForecastsReadingEngland

Personalised recommendations