Using seven-year (1979-1985) rawinsonde data in the equatorial region, the 30-60 day variation in the geopotential height (H) and the temperature (T) fields and their relations with fluctuations in the tonal wind (U) field are studied. After examining in detail the 30-60 day variation in the time series, the lag-correlation method is applied to the seven intervals of four month duration which show active variation. The main results are as follows: (i) In the H field of all the troposphere and the T field in the upper troposphere, the zonal standing-wave-like structures with a little phase differences are found in the wide region from India to Central America through the date line. (ii) In the lower troposphere, the 30-60 day variations of H and U are in phase near the date line, but the signal of U leads that of H by about 120° over the Maritime Continent. In the upper troposphere, the signal of U leads that of H by about 120° near the date line. (iii) Though the vertical structure has a large year-to-year variability, the upper tropospheric H leads the lower one by 70°-120° in the phase over the western and mid Pacific.
The properties of the H field obtained in the present work are considerably different from well-known ones in the U field. These results suggest that the simple Kelvin mode which has an out-of-phase structure between the upper and lower troposphere is not dominant in the 30-60 day variation.