Equatorial Wave intensity over the Indian Ocean during the Years 1968-1972

[摘要] By the use of data at three stations close to and near the equator over the Indian Ocean area, the intensity and the zonal propagation of equatorial waves are examined by spectral analysis for the four years from November 1968 to October 1972. Spectral estimates are computed for every three months, and two types of wave disturbances are detected throughout most of the four years though the intensity of their amplitudes fluctuates: (1) Eastward propagating wave disturbances of the zonal wind component and temperature with period of about 10-20 days carrying westerly momentum upward, and (2) Westward propagating wave disturbances of the meridional wind component with period of about 4-5 days. They appear to be Kelvin waves and mixed Rossby-gravity waves, respectively. Four-year averaged spectra are computed, and a climatological description is attempted for the basic situation of these two types of equatorial waves. Biennial and annual components of wave intensity are computed by simple Fourier transforms of time series of three-monthly spectral estimates. The phase relationship of biennial components to the quasi-biennial oscillation is roughly consistent with previous studies. Kelvin wave intensity near tropopause shows a marked annual cycle with the phase of maxima in April-July, nearly in phase with the westerly acceleration in the layer 70-100 mb and with the upper tropospheric easterly acceleration. Other types of equatorial waves have not yet been detected, though it is not conclusive if the disturbances of the zonal wind component above 30 mb are Kelvin waves.

[学科分类] 大气科学