Summary
The mean flow over East Africa at the 1.5 km level during May through September is presented. All available daily wind vectors from 1952–1973 for 22 pilot balloon stations were used.
The southeast-southwest monsoon current is a dominant feature. It is highly diffluent between 38 °E and 40 °E. There is little penetration inland as the current is blocked by the meridionally-oriented highlands. Vertical directional changes show general veering with height. The flow has maximum intensity in July–August with mean peak speeds of 15–17 m/s at 0600 GMT. The layer of strong winds lies between 0.3–2.5 km. Vertical wind shears increase from May, reach a maximum in June–July and decrease thereafter.
Zusammenfassung
Es wird die mittlere Strömung über Ostafrika in 1,5 km Höhe von Mai bis September präsentiert. Dazu werden alle verfügbaren täglichen Windvektoren von 1952 bis 1973 von 22 Pilotballonstationen herangezogen.
Die südöstliche bis südwestliche Monsunströmung ist ein dominierendes Kennzeichen. Sie divergiert stark zwischen 38 °E und 40 °E. Das weitere Eindringen landeinwärts wird durch die meridional orientierten Hochländer blockiert. Die vertikalen Richtungsänderungen zeigen eine allgemeine Drehung mit der Höhe. Die Strömung ist am kräftigsten im Juli und August mit mittleren Windspitzen von 15–17 m/s um 0600 GMT. Die Schicht starker Winde liegt zwischen 0,3 und 2,5 km Höhe. Die vertikale Scherung steigert sich beginnend im Mai, erreicht ein Maximum im Juni/Juli und verringert sich später wieder.
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References
Findlater, J.: A Major Low Level Air Current over the West Indian Ocean During Northern Summer. Quart. J. R. Met. Soc.95, 362–380 (1969).
Findlater, J.: Mean Monthly Air Flow at Low Levels over the West Indian Ocean. Geoph. Mem. No. 115 (HMSO, London, 1–115), 1971.
Findlater, J.: Aerial Exploration of the Low Level Cross-Equatorial Current over Eastern Africa. Quart. J. R. Met. Soc.98, 274–289 (1972).
Findlater, J.: The Low-Level Cross-Equatorial Air Current of the Western Indian Ocean During the Northern Summer. Weather29, 411–416 (1974).
Findlater, J.: Observational Aspects of the Low Level Cross-Equatorial Jet Stream of the Western Indian Ocean. Pure Appl. Geoph.115, 1251–1262 (1977).
Ngara, T.: Some Aspects of the East African Low Level Jet. M.Sc. thesis, Department of Meteorology, University of Nairobi, Kenya 1978.
Ardanuy, P.: On the Observed Diurnal Oscillation of the Somali Jet. Mon. Weath. Rev,107, 1694–1700 (1979).
Rao, G. V., van de Boogaard, H. M. E.: Structure of the Somali Jet Deduced from Aerial Observations Taken During June–July 1977. Monsoon Dynamics, Cambridge University Press, 322–331 (1981).
Ngara, T., Asnani, G. C.: Five-Day Oscillation in the East African Low Level Jet. Nature (London) 272, 708–709 (1978).
Krishnamurti, T. N., Bhalme, H. N.: Oscillations of a Monsoon System Part I: Observational Aspects. J. Atmos. Sci.33, 1937–1954 (1976).
Anderson, D. L. T.: The Low Level Jet as a Western Boundary Current. Mon. Weath. Rev.104, 907–921 (1976).
Hart, J. E.: On the Theory of the East African Low Level Jet Stream. Pure Appl. Geoph.115, 1263–1282 (1977).
Bannon, P. R.: On the Dynamics of the East African Jet. I: Simulation of Mean Conditions for July. J. Atmos. Sci.36, 2140–2152 (1979).
Bannon, P. R.: On the Dynamics of the East African Jet. II: Jet Transients. J. Atmos. Sci.36, 2153–2168 (1979).
Krishnamurti, T. N., Molarinari, J., Pan, H. L.: Numerical Simulations of the Somali Jet. J. Atmos. Sci.33, 2350–2362 (1976).
Cadet, D., Desbois, M.: A Case Study of a Fluctuation of the Somali Jet During the Indian Summer Monsoon. Mon. Weath. Rev.109, 182–187 (1971).
Semazzi, F. H. M.: Stationary Barotropic Flow Induced by Mountain over a Tropical Belt. Mon. Weath. Rev.108, 922–930 (1980).
Johnson, D. H.: Rain in East Africa. Quart. J. R. Met. Soc.88, 1–19 (1962).
Chaggar, T. S.: Geographical Distribution of Monthly and Annual Mean Frequency of Thunderstorm Days over Eastern Africa. East African Meteorological Department, Nairobi: Tech. Memo. No. 26, 1–22 (1977).
Samson, H. W., Gichuiya, S.: Hailstorms in the Kericho Area. East African Meteorological Department, Kenya (Nairobi), Tech. Memo. No. 22 (1971).
Kiangi, P. M. R., Kavishe, M. M., Patnaik, J. K.: Some Aspects of the Mean Tropospheric Motion Field in East Africa During the Long Rain Season. Kenya J. Science and Technology, Ser. A2, 91–103 (1981).
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Anyamba, E.K., Kiangi, P.M.R. Mean motion field in East Africa at the level of the East African low level jet core. Arch. Met. Geoph. Biocl., Ser. B 36, 29–41 (1985). https://doi.org/10.1007/BF02269455
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DOI: https://doi.org/10.1007/BF02269455