The purpose of this study is to examine the characteristics of equatorial waves identified in simulated atmospheric data by an NCAR global circulation model. The technique of wavenumber-frequency spectral analysis is applied for the time-sequence data at grid points around the latitude circles. Three types of dominant waves are identified by spectral peaks and phases: the atmospheric Kelvin waves, the mixed Rossby-gravity wave, and the Rossby-Haurwitz type of free oscillation. The Rossby-Haurwitz type of free oscillation is at zonal wavenumber 1 with a westward-propagating period of about 5 days. There is no vertical phase tilt for this oscillation. The Kelvin waves are found at wavenumber 1 with an eastward-traveling period of about 24 days and wavenumber 2 with an eastward-traveling period of about 12 days, while the mixed Rossby-gravity wave is found at zonal wavenumber 3 with a westward-traveling period of about 4.61 days. Both types of vertically-propagating waves have a vertical wavelength of about 8.5 km. The amplitude of the Kelvin wave is about the same order of magnitude as that observed in the real atmosphere, while the amplitude of the mixed Rossby-gravity wave is one order of magnitude smaller than that in the real atmosphere. The reason for the small amplitude of the mixed Rossby-gravity wave is discussed. In an effort to understand the origin and maintenance of the Kelvin waves, we also analyze the heating function and energy transport.
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Ching-Yen Tsay (1974) studied this question.