Abstract
Thermal properties of amplitude vacillation are studied experimentally. Use is made of a fluid annulus with the properly selected geometry to produce unmodulated baroclinic waves and a small number of temperature sensing probes so as to reduce the disturbing influences of probes on the flow field. Experiments, though conducted with only one value of imposed temperature difference, show that strong amplitude vacillation takes place virtually without the long wave (wavenumber=l) and the sidebands of the dominant wave. This exhibits a striking contrast to other experimental results (e. g. Hide et al., 1977; Pfeffer et al., 1980) obtained by using a large number of probes. The rate of radial heat transport and the azimuthally averaged temperature field vary with time with the same period as that of the amplitude vacillation. Further, nonlinear interaction between the azimuthally averaged temperature field and the deviations from it due to the waves (the dominant wave and its harmonics) is observed when the fluid is undergoing amplitude vacillation. These results indicate that amplitude vacillation is caused by baroclinic interactions between the waves and the azimuthally averaged flow field; although this simple mechanism was suggested in an earlier paper by Pfeffer and Chiang (1967), it has been somewhat confused by the subsequently observed sidebands.
