Rainfall in west central Africa

An estimation of the relative importance of various factors to the rainfall in West Central Africa has been attempted.The factors considered were tropical waves, monsoon depressions, the position of the intertropical discontinuity (ITO) and the tropical easterly jet stream (TEJ) of summer.Eleven years (1954)(1955)(1956)(1957)(1958)(1959)(1960)(1961)(1962)(1963)(1964) of daily rainfall amounts at 20 stations in Cameroun, Central African Republic, Congo, Gabon and Tchad were analyzed using spectral and cross spectral methods.The spectral results revealed the presence, at nearly all stations, of wavelike oscillations with periods ranging from 2.03 to 10.25 days, and periods of about 40 days or longer.Oscillations with periods 2.58 to 4.21 days and those with periods 40 days or longer showed significant coherence magnitudes and propagated from East to West with approximate wave lengths of 500 and 2000 km, respectively.Oscillations with periods 2.58 to 4.21 days have been interpreted as cloud clusters, very likely of the "disturbance line" type which usually associate with easterly waves.Oscillations with period 40 days have been tentatively interpreted as major rain-generating disturbances, perhaps of the monsoon depression type which are observed over the region in the summer months (June through September) when most of the rains fall.