5A.2
The role of upper tropospheric easterly waves on the synoptic time scale convection over East Africa
Ademe Mekonnen, SUNY, Albany, NY; and C. D. Thorncroft
Spectral analysis highlights the presence of 3-4 day significant periodic convection over central Sudan and Western Ethiopia during the boreal summer season, a region not well known for synoptic scale wave activity. In addition to a regional interaction between this region and the equatorial Congo (discussed in a companion presentation) we will show that this periodic convection exists due to upper-level easterly waves propagating along the tropical easterly jet from the Indian Ocean.
The structure and variability of easterly waves in the upper troposphere that are observed over East Africa during the boreal summer are explored using satellite brightness temperature data and ECMWF reanalyses. Composite analysis using a lag regression technique reveals that these waves are initiated over Southeast Asia. They are characterized by a wave-length of about 5000km, a periodicity of about 4-days and a phase speed of about 15ms-1, consistent with the few previous observational studies. Convection over tropical Africa tends to be enhanced in association with anomalous northerlies and suppressed in association with anomalous southerlies in the upper troposphere. Results show that the wave signals are observed before the convective signals appear over East Africa, suggesting that the upper tropospheric wave dynamics contribute to the development of convection over East Africa. We will present the mean structure and variability of these upper-level easterly waves including how they impact synoptic scale convection over East Africa.
Recorded presentationSession 5A, African Climate: V. Eastern and Southern Africa
Tuesday, 22 January 2008, 8:30 AM-9:45 AM, 215-216
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