An amplitude vacillation observed in a laboratory experiment is simulated using a three-dimensional global grid numerical model. The time variations of energy components and internal structures revealed by the numerical solutions show that the amplitude vacillation consists of the stages of the buildup and breakdown of the zonal available potential energy accompanied by the decay and growth of baroclinic waves, respectively. The spectral analysis indicates that the mechanism of this amplitude vacillation is the non-linear interaction between a single dominant wave and the zonal flow. This is in a great contrast to another explanation by the interference of two waves with the same azimuthal wavenumber and different phase speeds (e. g., Buzyna et al., 1989).
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