Rotating Rayleigh-Bénard convection: Aspect-ratio dependence of the initial bifurcations

The initial bifurcations in rotating Rayleigh-B\'enard convection are studied in the range of dimensionless rotation rate $0 < \Omega < 2150$ for an aspect-ratio-2.5 cylindrical cell. We used simultaneous optical shadowgraph, heat transport and local temperature measurements to determine the stability and characteristics of the azimuthally-periodic wall convection state. We also show that the second transition corresponds to the onset of bulk convection. Our results for critical Rayleigh numbers, precession frequencies and critical mode numbers agree well with theoretical results. The dynamics of the wall convection state can be described by a complex Ginzburg-Landau amplitude equation.