A Further Study of Tropical Wave Disturbances by the Use of Spectrum Analysis

Abstract

The upper wind data of the tropical Pacific stations during the period April through July 1962, which were previously studied by Yanai et al. (1968), are re-examined with respect to both the zonal and meridional wind components covering a wider spectral range from 2 to 25 day periods. A few new samples are added to study the wave disturbances in the western Pacific south of the equator. The results of the power spectrum analysis are presented in height frequency diagrams. Besides the previously known 4- to 5-day periodicity of the meridional wind component, a pronounced zonal wind oscillation with periods longer than 10 days is found throughout the entire troposphere and the lower stratosphere at most of the stations. A periodicity near 7 days in the zonal component is isolated at some stations. All of the major spectral peaks show a maximum concentration of power density in the upper troposphere. Regional differences in the spectral density distribution in the height-frequency diagrams are examined. A preliminary consideration of the interpretation of the time series analysis is also made.