On the 3-4 day periodic convection over East Africa

Spectral analysis using long-term brightness temperature data highlights the presence of pronounced and significant 3-4 day periodicity in convection over central Sudan and adjacent western Ethiopia during the boreal summer season, a region not well known for synoptic scale wave activity. Composite analysis using a lag regression technique indicates that much of this variability arises in association with (a) a regional convective oscillation that takes place between East Africa and the equatorial Congo region, and (b) upper level easterly waves that originate over Southeast Asia and propagate across tropical Africa.

Observations show the presence of anomalous out-of-phase convective oscillation between equatorial Africa and East Africa. Consistent with this there is a marked variation in the moisture transport between the two regions. Results also show that the easterly wave signals in the upper troposphere are often observed before the convective signals over East Africa, suggesting that upper tropospheric wave dynamics may contribute to the development of convection separate from any regional interaction.