Asymmetric modes and the transition to vortex structures in rotating Rayleigh-Bénard convection

Abstract

We report heat transport measurements and optical shadowgraph visualization of rotating Rayleigh-Bénard convection. For dimensionless rotation rates 140<ΩR much less than the linear-stability value for roll or vortex states, is a forward Hopf bifurcation to an azimuthally asymmetric state with mode number n. States with n=3, 4, 5, 6, and 7 exist at low to moderate R and precess with frequencies that depend on R and Ω. At higher R there is a continuous transition to a state with noisy, time-dependent heat transport, a distinct array of vortices in the central region, and a modulation of the precession speed of the outer structures.