Supporting data for "Experimental Studies of Turbulent Thermal Convection with Rotation and Latitudinal Libration"

Turbulent convective flows in geophysics and astrophysics are greatly affected by the celestial body's rotation. For instance, the famous Hadley cell in the atmosphere of Earth is considered a global tropical circulation caused by the combination of convection and rotation. In addition, the rotational dynamics of planetary bodies are not always constant but perturbed by gravitational interactions with their orbital partners. Motivated by these, turbulent thermal convection with rotation and latitudinal libration (one kind of perturbation) are experimentally studied in this thesis.

First, the properties of heat transport and flow structures in rotating thermal convection are experimentally investigated. The heat transport efficiency exhibits a scaling transition at a transitional Ekman number Ek_c, at which sharp transitions of the dynamical and geometrical properties of the columnar structures also occur. This excellent correspondence reveals that the behaviours of heat transfer efficiency are intimately related to the changes in coherent structures in the bulk flow, which in turn does not support the alternative boundary layer-competition mechanism. The sharp transition at Ek_c also provides the first crystal-clear experimental evidence for the regime transition from convective Taylor column regime to plume regime, at which the columns break down due to the increased inertial effect. These results offer insights into the planetary dynamo studies, especially for the dipole reversals of the geodynamo near the dipole-multipole transition.

Second, the weak centrifugal effects in rotating thermal convection are investigated experimentally. The analysis of the flow field reveals that in contrast to instantaneous quantities, the influence of the weak centrifugal force on long-time averaged quantities cannot be ignored. Therefore, the onset issue of centrifugal effects is studied systematically by the long-time averaged bulk temperatures, and the onset Froude number Fr_c is found to scale with the Rayleigh number (Ra) as Fr_c~Ra^0.55. This 0.55 scaling can be reasonably well explained by the measured results of inter-column distance l₀, which is related to Fr_c through a local force balance argument. In addition, the standard deviations of the bulk temperatures are analyzed to show well power-law scalings with both Ra and Ek.

Finally, we report an experimental study on the effects of latitudinal libration on rotating thermal convection. Forced inertial modes obtained from the proper orthogonal decomposition (POD) take the form of an azimuthally travelling wave, which traps hot and cold fluid near thermal boundary layers, thus inhibiting the global heat transport properties. In particular, this heat transport inhibition is strongly enhanced when the forced inertial modes are amplified by the direct resonance. However, the heat transfer inhibition also becomes smaller when this amplification is weakened with intensified convection. These results may provide some implications for why Mercury has a large amount of water ice buried at its north and south poles.