Onset of traveling waves in isothermal double diffusive convection

Experiments on double diffusive convection sustained by imposed vertical concentration gradients have been conducted in a novel thin isothermal parallelepiped cell. The measured critical Rayleigh number and the frequency of traveling waves are in reasonable accord with a stability analysis that predicts a tricritical condition all along the instability boundary. Visualization of the pattern from the side reveals that the asymptotic state immediately above the onset of instability consists of packets of traveling finite amplitude plumes.