Temperature fluctuations relevant to thermal-plume dynamics in turbulent rotating Rayleigh-Benard convection

We present measurements of temperature fluctuations in turbulent rotating Rayleigh-Benard convection. The temperature variance exhibits power-law dependence on the fluid height outside the thermal boundary layers irrespective of the rotating rates. Rotations increase the magnitudes of temperature variance, but reduce the skewness and kurtosis, leading to Gaussian-like temperature distributions. We derive a general theoretical expression for all statistical moments of temperature in terms of the dynamical properties of the thermal plumes, based on the findings that both the amplitude and time width of thermal plumes are log-normally distributed. Our model replicates the statistical properties of the temperature fluctuations and reveals the physical origin of their rotation dependence. Rotations increase the temperature amplitude of thermal plumes by virtue of the Ekman pumping process, but reduce the variations of the plume amplitude in time, presumably through the suppression of turbulent mixing between the plumes and the ambient fluid.