Thermal Convection in a Large Rotating Fluid Annulus: Some Effects of Varying the Aspect Ratio

Abstract

Previous experiments on thermal convection in a rotating fluid annulus (of depth d, inner radius a and outer radius b subject to an impressed horizontal temperature contrast ?T have been extended to very small values of the aspect ratio and the dependence on ? and other parameters of (Θc the value of the dimensionless parameter Θ=gd?p at the transition, due to baroclinic instability, from axismmetric to non-axisymmetric flow. (Here g denotes acceleration due to gravity, ?p/p is the fractional density contrast corresponding to ?T, and determinations of σ2 in the non-axisymmetric regime show that its value is comparatively unaffected by the presence of baroclinic waves. Experimental values of Θc for values of ?<1 when the effects of viscosity are important, are compatible both quantitatively and qualitatively with theories of the effect of Ekman layer friction on Eady's theory of baroclinic instability. Furthermore, the values of the wavenumber close to the transition from axisymmetric to non-axisymmetric flow, for all values of ? considered, are in reasonable agreement with the linear theories.