Time Dependence of Flow Patterns near the Convective Threshold in a Cylindrical Container

Digitally processed shadowgraph images revealed time-dependent flow patterns slightly above the convective onset in a cylindrical cell of aspect ratio $L\equiv \frac{D}{2d}=15.0\mathrm{}$ ($D$ is diameter, $d$ is height). This time dependence was monitored for up to 200 horizontal thermal diffusion times. At larger Rayleigh numbers, the system reached time-dependent states after much shorter transients.