Spectral and cross-spectral analysis are used to investigate the existence and structure of wave-type disturbances in the troposphere over the equatorial South Atlantic Ocean. The data, which came from the NMCs tropical analysis, consists of wind components for five levels of the troposphere 700 to 200 mb and comprise a period of 411 days. Also data at the stations Parnaiba Airport 3 degrees S, 42 degrees W and Ascension Island 8 degrees S, 14 degrees W are examined. The spectral results indicate, with 95 confidence, that there is periodicity in the time-series analysed in the frequency band 0.16-0.24 cpd approximately 4- to 6- day periods. Cross-spectral analysis results indicate that the disturbance has a wavelength of about 6000 km, propagates westward at a rate of about 11 degrees longitude per day, has a slight NW-SE tilt and tilts backward in the vertical.