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Abstract:

AbstractWhen a fluid system is subject to strong rotation, centrifugal fluid motion is expected, i.e., denser (lighter) fluid moves outward (inward) from (toward) the axis of rotation. Here we demonstrate, both experimentally and numerically, the existence of an unexpected outward motion of warm and lighter vortices in rotating thermal convection. This anomalous vortex motion occurs under rapid rotations when the centrifugal buoyancy is sufficiently strong to induce a symmetry-breaking in the vorticity field, i.e., the vorticity of the cold anticyclones overrides that of the warm cyclones. We show that through hydrodynamic interactions the densely distributed vortices can self-aggregate into coherent clusters and exhibit collective motion in this flow regime. Interestingly, the correlation of the vortex velocity fluctuations within a cluster is scale-free, with the correlation length being proportional ( ≈ 30%) to the cluster length. Such long-range correlation leads to the counterintuitive collective outward motion of warm vortices. Our study brings insights into the vortex dynamics that are widely present in nature.

Abstract:

The tidal evolution of interacting binaries when the orbital period is short compared to the primary star's convective time scale is a problem of long-standing. Terquem (2021) has argued that, when this temporal ordering scheme is obeyed, the rate of energy transfer from tides to convection (denoted $D_R$) is given by the product of the averaged Reynolds stress associated with the tidal velocity and the mean shear associated with the convective flow. In a recent response, Barker and Astoul (2021, hereafter BA21) claim to show that $D_R$ (in this form) cannot contribute to tidal dissipation. Their analysis is based on a study of Boussinesq and anelastic models. Here, we demonstrate that BA21 misidentify the correct term responsible for energy transfer between tides and convection. As a consequence, their anelastic calculations do not prove that the $D_R$ formulation is invalidated as an energy-loss coupling between tides and convection. BA21 also carry out a calculation in the Boussinesq approximation. Here, their claim that $D_R$ once again does not contribute is based on boundary conditions that do not apply to any star or planet that radiates energy from its surface, which is a key dissipational process in the problem we consider.

Abstract:

Internal redox reactions may irreversibly alter the mantle composition and volatile inventory of terrestrial and super-Earth exoplanets and affect the prospects for atmospheric observations. The global efficacy of these mechanisms, however, hinges on the transfer of reduced iron from the molten silicate mantle to the metal core. Scaling analysis indicates that turbulent diffusion in the internal magma oceans of sub-Neptunes can kinetically entrain liquid iron droplets and quench core formation. This suggests that the chemical equilibration between core, mantle, and atmosphere may be energetically limited by convective overturn in the magma flow. Hence, molten super-Earths possibly retain a compositional memory of their accretion path. Redox control by magma ocean circulation is positively correlated with planetary heat flow, internal gravity, and planet size. The presence and speciation of remanent atmospheres, surface mineralogy, and core mass fraction of primary envelope-stripped exoplanets may thus constrain magma ocean dynamics.