Kinematic Properties of Wave Amplitude Vacillation in a Thermally Driven Rotating Fluid

Abstract

Empirical evidence is presented to the effect that amplitude vacillation in a thermally driven rotating annulus of fluid is due primarily to the interference of two modes with the same azimuthal wavenumber and different vertical structures and phase speeds. Higher order details of the amplitude vacillation cycle are attributable to one or two additional modes that are generated by the interaction of the primary pair with the mean zonal flow (i.e., wave-mean flow interactions). Wave-wave interactions appear to play a negligible role in accounting for amplitude vacillations observed in laboratory experiments. Sufficient theoretical evidence is available in the published literature to suggest that the two fundamental modes responsible for amplitude vacillation arise through the destabilization of neutral Eady modes by one or more critical layers in the fluid.