Mean flow precession and temperature probability density functions in turbulent rotating convection

Laboratory results for high Rayleigh number convection in a rotating cylinder heated from below are presented. Time series of temperature fluctuations reveal: (a) There is a large-scale overturning meridional cell that precesses in the retrograde direction (opposite to the direction of the basic rotation) when viewed from the coordinates attached to the container. This precessing cell is prevalent at low to medium basic rotation rates, but is suppressed when the thermal Rossby number becomes less than about one half. (b) The temperature fluctuations at the centerpoint of the apparatus display a transition from nearly exponential, to Gaussian, then back to toward an exponential probability density function as the Taylor number is raised. The Rayleigh number required for Gaussian statistics is of order 1010. As the Rayleigh number increases, the Taylor number interval over which nearly Gaussian statistics are found becomes wider. These findings agree with previous turbulent rotating convection experiments at lower Rayleigh number in which Gaussian statistics were not observed.