The study consists of two parts: a detailed investigation of wave disturbances in the tropical lower troposphere during a single 6 month period, and a brief survey of wave activity at a single station during four successive 6-month periods. Cross spectrum analysis of wind, temperature, relative humidity and surface pressure data reveals the existence of at least three types of disturbances: Easterly waves, with periods in the range of 4–5 days and horizontal wavelengths on the order of 3000 km. Contrary to the results of earlier studies, the axes of the waves show no inclination with height. There is some indication of a cold core structure, but the temperature fluctuations in the waves are very small. Some stations show a tendency for high relative humidities to occur in the troughs of the waves, in agreement with earlier studies. Low-frequency oscillations with periods >10 days and horizontal wavelengths on the order of 10,000 km. These are most strongly evident in the zonal wind component, for... Abstract The study consists of two parts: a detailed investigation of wave disturbances in the tropical lower troposphere during a single 6 month period, and a brief survey of wave activity at a single station during four successive 6-month periods. Cross spectrum analysis of wind, temperature, relative humidity and surface pressure data reveals the existence of at least three types of disturbances: Easterly waves, with periods in the range of 4–5 days and horizontal wavelengths on the order of 3000 km. Contrary to the results of earlier studies, the axes of the waves show no inclination with height. There is some indication of a cold core structure, but the temperature fluctuations in the waves are very small. Some stations show a tendency for high relative humidities to occur in the troughs of the waves, in agreement with earlier studies. Low-frequency oscillations with periods >10 days and horizontal wavelengths on the order of 10,000 km. These are most strongly evident in the zonal wind component, for...