No abstract

The power spectra of the meridional component of the wind from the ground to the 30-km level at 17 stations in the tropical and sub-tropical Pacific are studied based on special upper wind observations taken during the period April through July 1962.In equatorial latitudes, the power spectra show a peak at a period close to 4 days corresponding to the passage of "equatorial waves" in the lower tropospheric easterlies. A very large spectral density is found at the periods 4 to 5 days throughout the upper troposphere and the lower stratosphere where the mean wind is from the west. The peak spectral density reaches a maximum at about the 17-km level near the tropopause. The spectral density gradually decreases with height in the stratosphere where the mean wind is from the east.In sub-tropical latitudes, large disturbance energy is associated with the upper tropospheric westerlies and a large portion of the spectral density is contained in the wave period longer than 5 days. A sharp suppression of the spectral density takes place at the lower boundary of the stratospheric easterlies.From the computation of the coherence and the phase difference of the meridional component of the wind, the vertical and horizontal structure of the disturbances is studied. The large horizontal extent and the westward inclination of phase lines of the disturbances in the upper troposphere and in the lower stratosphere are revealed. The horizontal coherence of the lower tropospheric disturbances in the east-west direction is very low. The phase lines of the lower tropospheric disturbances are inclined eastward with height. The average wavelength of the disturbances at various levels is estimated from the relation between the phase difference and the longitudinal difference of the stations.

A power spectral analysis is made for the data of upper winds at Canton Island (S 02°46", The vertical extent of the disturbances is roughly 4 km on the average. The phase of the disturbances at lower levels lags behind that at upper levels. The phase lines of the disturbances tilt westward with height, in consideration of their westward propagation supported by additional synoptic analyses.

Westward-moving wave disturbances in the westerlies of the equatorial lower stratosphere recently found by Yanai and Maruyama (1966) are studied in detail by using the data of the special observations over the Marshall Islands area during spring and summer in 1958. Vertical time-sections of upper winds show that the wind direction at about 18 to 24 km height oscillates between southwest and northwest with a period of four to five days. Synoptic analysis shows the existence of the large-scale wave disturbances moving westward against the westerly flow at a speed of about 2,000 km/day.

No abstract