Summary
Using the ECMWF and NMC analyses, this study documents the composite structures of the African and of the 6–9 day waves. In spite of the fact that the two types of disturbances develop over almost the same area, i.e. Central and West Africa and the tropical Atlantic, during the same season, i.e. summer, in spite of the fact that they have almost the same East-West velocity, i.e. 7–8 degree longitude per day, the structures of the two waves are very different.
At 12.5°N, the African wave has an amplitude maximum in the meridional wind component whilst the zonal wind component is almost unperturbed. On the contrary, in the 6–9 day wave, at 12.5°N and also at 12.5°S, the zonal wind component has an amplitude maximum whilst the meridional wind component is very small and there is an amplitude maximum for the meridional wind component at the equator and 20°N.
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References
Adefolalu, D. O., 1974: On scale interactions and the lower tropospheric summer easterly perturbation in Tropical West Africa.Ph.D. The Florida State University School of Arts and Sciences. Department of Meterology.
Burpee, R. W., 1972: The origin and structure of easterly waves in the lower troposphere in North Africa.J. Atmos. Sci.,29, 77–90.
Burpee, R. W., 1974: Characteristics of North African easterly waves during the summers of 1968 and 1969.J. Atmos. Sci.,31, 1556–1570.
Burpee, R. W., 1975: Some features of synoptic-scale waves based on a compositing analysis of GATE data.Mon. Wea. Rev.,103, 921–925.
Cadet, D. L., Houston, S. H., 1984: Precipitable water over Africa and the Eastern/Central Atlantic ocean during the 1979 summer.J. Meteor. Soc. Japan,62, 761–774.
Carlson, T. N., 1969a: Synoptic histories of three African disturbances that developed into Atlantic hurricanes.Mon. Wea. Rev.,97, 256–276.
Carlson, T. N., 1969b: Some remarks on African disturbances and their progress over the tropical Atlantic.Mon. Wea. Rev.,97, 716–726.
De Felice, P., Viltard, A., Monkam, D., Ouss, C., 1990: Characteristics of North African 6–9 day waves during summer 1981.Mon. Wea. Rev.,118, 2624–2633.
De Felice, P., Viltard, A., Oubuih, J., 1992: A synoptic-scale wave of 6–9 day period in the Atlantic tropical troposphere during summer 1981.Mon. Wea. Rev.,121, 1291–1298.
Duvel, J. P., 1990: Convection over tropical Africa and the Atlantic Ocean during northern summer. Part II: modulation by easterly waves.Mon. Wea. Rev.,118, 1855–1868.
Krishnamurti, T. N., Bhalme, H. H., 1976: Oscillations of a monsoon system. Part 1. Observational aspects.J. Atmos. Sci.,33, 1937–1954.
Krishnamurti, T. N., Subramaniam, M., Oosterhof, D. K., Daughenbough, G., 1990: Predictability of low frequency modes.Meteorol. Atmos. Phys.,44, 63–83.
Piersig, W., 1936: Schwankungen von Luftdruck and Luftbewegung sowie ein Beitrag zum Wettergeschehen im Passatgebiet des östlichen nordatlantischen Ozeans.Arch. Dtsch. Seewarte,54(n6).
Reed, R. J., Recker, E. E., 1971: Structures and properties of synoptic-scale wave disturbances in the equatorial western Pacific.J. Atmos. Sci.,28, 1117–1133.
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.,105, 317–333.
Reed, R. J., Hollingsworth A., Heckley, W. A., Delsol, F., 1988a: An evaluation of the performance of the ECMWF operational system in analysing and forecasting easterly wave disturbances over Africa and the tropical Atlantic.Mon. Wea. Rev.,116, 824–865.
Reed, R. J., Klinder, E., Hollingsworth, A., 1988b: The structure and characteristics of African easterly wave disturbances determined from ECMWF operational analysis/forecast system.Meteorol. Atmos. Phys.,38, 22–33.
Regula, H., 1936: Druckschwankungen und Tornados an der Westküste von Afrika.Ann. Hydrogr. Mar. Meteor.,64, 107–111.
Riehl, H., 1948: On the formation of typhoons.J. Meteor.,5, 247–264.
Sèze, G., Rossow, W. B., 1991a: Time-culminated visible and infrared radiance histograms used as a descriptor of surface and cloud variation.Int. J. Remote Sensing,12, 877–921.
Sèze, G., Rossow, W. B., 1991b: Effects of satellite data on measuring the space/time variations of surfaces and clouds.Int. J. Remote Sensing,12, 921–952.
Viltard, A., de Felice, P., 1979: Statistical analysis of wind velocity in an easterly wave over West Africa.Mon. Wea. Rev.,107, 1320–1327.
Wallace, J. M., 1973: General circulation of the tropical lower stratosphere.Rev. Geophys. Space Phys.,17, 191–222.
Yanai, M., Murakami, M., 1970: Spectrum analysis of symmetric anti-symmetric equatorial waves.J. Meteor. Soc. Japan,48, 331–346.
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Viltard, A., de Felice, P. & Oubuih, J. Comparison of the African and the 6–9 day wave-like disturbance patterns over West-Africa and the tropical Atlantic during summer 1985. Meteorl. Atmos. Phys. 62, 91–99 (1997). https://doi.org/10.1007/BF01037482
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DOI: https://doi.org/10.1007/BF01037482