Time-dependent patterns in the two-layer Rayleigh-Bénard system

We report experiments on the two-layer Rayleigh-B\'enard system with two different pairs of fluids and with both rectangular and annular geometries. Theoretical studies have shown that in addition to two distinct stationary states, it is possible to have time-dependent patterns at or near convective onset. We have found a traveling wave pattern at the onset to convection using silicone oil over water. Standing and traveling wave states have been found slightly above the onset to convection in a system of silicone oil over Fluorinert™. The basic form of these time-dependent states is consistent with the predictions, while some of the quantitative properties of the states depend on the system geometry.