Plume Motion and Large-Scale Circulation in a Cylindrical Rayleigh-Bénard Cell

We used the time correlation of shadowgraph images to determine the angle of the horizontal component of the plume velocity above (below) the center of the bottom (top) plate of a cylindrical Rayleigh-B\'enard cell of aspect ratio /L=1 (D is the diameter and L87 mm is the height) in the Rayleigh-number range 710^7310^9 for a Prandtl number =6. We expect that gives the direction of the large-scale circulation. It oscillates time periodically. Near the top and bottom plates (t) has the same frequency but is anticorrelated.