Abstract
Spectrum analysis of wind, temperature, geopotential height and relative humidity fluctuations in the troposphere of the tropical Pacific is made during the period April through July 1962. As noted by Yanai et al. (1968), the power spectra of the meridional wind component show a peak in the period range 4 to 5 days in the troposphere. The peak in the lower troposphere corresponds to the passage of "easterly waves". There is a weak indication of the corresponding peaks in the spectra of other parameters in the western Pacific.
The wavelength of the tropospheric waves with the 4- to 5-day periods is estimated from the phase difference of the meridional wind component between separated stations. The wavelength in the lower troposphere is distinctly different between the eastern Pacific and the western Pacific. The wavelength is 8, 000 to 10, 000km in the eastern Pacific, while it is 5, 000 to 6, 000 km in the western Pacific.
The tropospheric wave has a tilt of the wave axis directed from southwest to northeast in the northern hemisphere. The axis is directed from northwest to southeast in the southern hemisphere. The phase lines of the lower tropospheric disturbances are inclined eastward with height and the inclination becomes smaller as the waves progress into the western Pacific. Phase relations between the meridional wind component and other parameters are studied. The coherences among them are relatively large in the western Pacific but they are small in the eastern Pacific. A schematic picture of the structure of the tropospheric wave in the western Pacific is presented. A cold air lies to the east of the wave axis in the lower troposphere and a warm air lies above the cold air. The maximum relative humidity is also situated to the east of the wave axis in the lower troposphere.
