Observation of coexisting upflow and downflow hexagons in Boussinesq Rayleigh-Benard convection

We experimentally observed patterns consisting of domains of upflow hexagons coexisting with domains of downflow hexagons in Boussinesq Rayleigh-Benard convection. The sequence of patterns, as the control parameter epsilon = Delta T/Delta T-c - 1 is increased, is from ordered or disordered rolls at onset to extended targets and spirals at epsilon - 1, to coexisting hexagons at epsilon similar to 3. Hexagons occur for all values of the Prandtl number 2.8 less than or equal to P less than or equal to 28 investigated. Surprisingly, they appear in a range where only rolls were known to be stable, and their wave number differs substantially from the roll wave number they coexist with.