Meteorological Aspects of the Congo Basin and Western Equatorial Africa

Abstract

This article focuses on the Congo basin and western equatorial Africa (WEA). Topics include atmospheric circulation, convective systems, the character of rainfall, cloud cover, moisture and evapotranspiration, and interannual variability. Some misunderstanding exists about the seasonal cycle. It has generally been described as bimodal, with rainy seasons in the boreal spring and autumn as the Intertropical Convergence Zone (ITCZ) transits the region. This is true of only some central portions and some of the region has a unimodal seasonal cycle. More importantly, the ITCZ does not exist in this region. Intraseasonal variability is related to equatorial waves, the most important being convectively-coupled Kelvin waves and the Madden-Julian Oscillation. Main circulation features are the Tropical Easterly Jet, two mid-tropospheric African Easterly Jets, and low-level westerlies. A Walker cell exists over the region in some seasons. There is also evidence of a shallower, Walker-type cell in the Congo basin itself. The Congo basin is the site of the world's strongest convective activity, including the world's highest lightning frequency. Dominant are Mesoscale Convective Systems, which bring convective rainfall in the afternoon and stratiform rainfall at night. As for rainfall, there is little correlation on monthly or annual time scales between rainfall at various stations. The factors in interannual variability in the Congo basin are not well understood. In WEA sea-surface temperatures are important. El Niño-Southern Oscillation appears to have little influence, but the Indian Ocean dipole has some influence in the east. Other factors include changes in the Walker circulation, the African thermal lows, and the low-level westerlies.