We present measurements of the orientation ${\theta }_0(t)$ of the large-scale circulation (LSC) of turbulent Rayleigh-Bénard convection in cylindrical cells of aspect ratio 1. ${\theta }_0(t)$ undergoes irregular reorientations. It contains reorientation events by rotation through angles $\Delta \theta$ with a monotonically decreasing probability distribution $p(\Delta \theta )$, and by cessations (where the LSC stops temporarily) with a uniform $p(\Delta \theta )$. Reorientations have Poissonian statistics in time. The amplitude of the LSC and the magnitude of the azimuthal rotation rate have a negative correlation.

• Received 18 March 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.084503