We present an experimental study of thermal plumes growing in Hele-Shaw cells which shows the existence of new objects, analogous to Saffman-Taylor fingers, for which the thermal boundary layer plays the role of the interface. The theoretical analysis reveals the underlying selection mechanism, which is provided by heat diffusion.

• Received 12 August 1991

DOI:https://doi.org/10.1103/PhysRevLett.69.601