Meteorology and Atmospheric Physics

, Volume 66, Issue 1–2, pp 51–63 | Cite as

Spatial evolutions of the active convective patterns across the Equatorial Eastern Africa region during northern hemisphere spring season using Outgoing Longwave Radiation records

  • R. E. Okoola


This study has used low Outgoing Longwave Radiation (OLR) values to study the structure and evolution of the active convection across Equatorial Eastern Africa (EEA) region (5° N to 10° S, 28° E to 42° E) during the northern hemisphere spring season. This involved the examination of the map patterns and cross-sections of OLR data as derived from once-daily NOAA's Operational Polar Orbiting satellites within the period June 1974 to May 1991.

The results from the study indicated that before March the mean ITCZ was active over the west Indian Ocean and Central Africa. The migration northwards of the zone of active ITCZ was associated with pre-season evolution patterns over the extratropics. The time-longitude cross-sections further indicated evidence that low OLR values were already occurring over central Africa to the west of 35° E before March. Such low OLR values penetrated to the east of 35° E in some occasions. Theresults from the study suggest that behind the surges of extratropical frontal systems strong meridional flow does occur and that these are associated with the advance of the ITCZ further northwards from extratropical regions of southern Africa. Then, active convection occurred over EEA region and this extended westwards to cover West Africa as well. The withdrawal of the ITCZ from the EEA region was however associated with the establishment of a centre of low OLR values to the southwest of Peninsula India.

The results from the study further revealed that the years 1981/1984 has the lowest/highest mean OLR values in the region within the period 1974 to 1991. The time-latitude cross-sections of the anomalous years indicated that active convection crossed the EEA region from south to north of the equator early/late during the anomalous wet/dry years of 1981/1984. The number of pentads with low OLR were also more/less during 1981/1984 respectively.


Outgoing Longwave Radiation Active Convection Operational Polar Polar Orbit Meridional Flow 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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  1. Anyamba, E. K., 1992: Some properties of a 20–30 day oscillation in tropical convection.J. African Met. Soc.,1, 1–19.Google Scholar
  2. Asnani, G. C., 1993:Tropical Meteorology, Published by Prof. G. C. Asnani, Pune, IndiaGoogle Scholar
  3. Brode, R. W., Mak, M. K., 1981: On the monsoonal midtropospheric cyclogenesis over western India. In: Lighthill, J., Pearce, R., (eds.)Monsoon Dynamics, 365–380. Cambridge University Press.Google Scholar
  4. Datta, R. K., 1981: Certain aspects of monsoonal precipitation dynamics over Lake Victoria. In: Lighthill, J., Pearce, R., (eds.)Monsoon Dynamics, 333–350. Cambridge University Press.Google Scholar
  5. Folland, C. K., 1983: Regional-Scale interannual variability of climate. A north-west European perspective.Met. Mag.,112, 163–187.Google Scholar
  6. Gruber, A., Krueger, A. F., 1984: The status of NOAA OLR dataset.Bull. Amer. Meteor. Soc.,65, 958–962.Google Scholar
  7. Gunn, B. W., McBride, J. L., Holland, G. J., Keenan, T. D., Davidson, N. E., Hendon, H. H., 1989: The Australian Summer monsoon circulation during AMEX Phase II.Mon. Wea. Rev.,117, 2554–2574.Google Scholar
  8. Lau, K. M., Chan, P. H., 1983: Short-term climate variability and atmospheric teleconnections from satellite observed Outgoing Longwave Radiation. Part I: Simultaneous relationships. Part II: Lagged Correlations.J. Atmos. Sci.,40, 2735–2767.Google Scholar
  9. Mak, M. K., 1975: The monsoonal mid-tropospheric cyclogenesis.J. Atmos. Sci.,32, 2246–2253.Google Scholar
  10. Matarira, C. H., Jury, M. R., 1992: Contrasting Meteorological Structure of intraseasonal wet and dry spells in Zimbabwe.J. Climatol.,12, 165–176.Google Scholar
  11. Matsumoto, J., 1992: The seasonal changes in Asian and Australian monsoon regions.J. Meteor. Soc. Japan.,70, 257–273.Google Scholar
  12. Moron, V., 1995: Variability of the African Convection Centre as viewed by Outgoing Longwave Radiation records and relationships with surface temperature patterns.J. Climatol.,15, 25–34.Google Scholar
  13. Mukabana, J. R., Pielke, R. A., 1996: Investigating the Influence of Synoptic-scale Monsoonal Winds and meso-scale circulation on diurnal weather patterns over Kenya using a Numerical Model.Mon. Wea. Rev.,124, 224–243.Google Scholar
  14. Mukherjee, A. K., Rao, M. K., Shah, K. C., 1978: Vortices embedded in the trough of low pressure off Maharashtra-Goa coasts during the month of July.Indian J. Met. Hydrol. Geophys.,29, 61–65.Google Scholar
  15. Okoola, R. E., 1997: Characteristics of the ITCZ over Equatorial Eastern Africa based on station rainfall records.J. African Met. Soc., (In press).Google Scholar
  16. Okoola, R. E., 1996: Space-Time characteristics of the ITCZ over Equatorial Eastern Africa during anomalous rainfall years. Ph. D Thesis, Dept. of Met., University of Nairobi.Google Scholar
  17. Shinoda, M., 1990: A climatological study on drought in the semi-arid region of tropical Africa. Ph. D thesis, Dept. of Geography, Tokyo Metropolitan University.Google Scholar
  18. Tomsett, J. E., 1975: The diurnal variation of precipitation in East Africa.E. A. M. D., Tech. Memo,25, 66pp.Google Scholar
  19. Waliser, D. E., Gautier, C., 1993: A satellite derived climatology of the ITCZ.J. Climate,6, 2162–2173.Google Scholar
  20. Ward, M. N., 1992: Provisionally corrected surface wind data, world-wide ocean-atmosphere surface fields and Sahelian rainfall variability.J. Climatol.,5, 454–475.Google Scholar

Copyright information

© Springer-Verlag 1998

Authors and Affiliations

  • R. E. Okoola
    • 1
  1. 1.Department of MeteorologyUniversity of NairobiKenya

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