Statistics of temperature and velocity fluctuations in supergravitational convective turbulence.

We report an experimental study of the temperature and velocity fluctuations in supergravitational turbulent convection system. The negative spikes of the time series of temperature fluctuations appear periodically, which may result from the azimuthal movement of the cold plumes in the rotating frame pushed by the zonal flow. The period τ0 decreases slightly with increasing Rayleigh number (Ra) and τ0 is over one order larger than the time scale of the large-scale circulation. In addition, the temperature frequency power spectra follow P(f) ∼ f−5 for different Ra over the range 2 ≾ f ≾ 10, implying the possible existence of inverse cascade due to turbulence in equilibrium with zonal flow. The Rhines frequency fβ at which the inverse cascade ceases is around half of a decade smaller than the smallest frequency of the −5 scaling range. Further, the azimuthal distribution of the time-averaged radial velocity has no obvious peak and trough, which provides further evidence for the existence of zonal flow. Additionally, it is found that the probability density function for temperature and velocity fluctuations in the current system can be well fitted with the model (Wang et al. 2019, 2022) for the classical Rayleigh-Bénard convection. [ABSTRACT FROM AUTHOR]