Shadowgraph Measurements of Rotating Convective Planetary Core-Style Flows

Abstract

The local scale of rotating convection, ℓ, is a fundamental parameter in many turbulent geophysical and astrophysical fluid systems, yet it is often poorly constrained. Here we conduct rotating convection laboratory experiments analogous to convecting flows in planetary cores and subsurface oceans to obtain measurements of the local scales of motion. Utilizing silicone oil as the working fluid, we employ shadowgraph imagery to visualize the flow, from which we extract values of the characteristic cross-axial scale of convective columns and plumes. These measurements are compared to the theoretical values of the critical onset length scale, ℓ_crit, and the turbulent length scale, ℓ_turb. Our experimentally obtained length scale measurements simultaneously agree with both the onset and turbulent scale predictions across three orders of magnitude in convective supercriticality $\left(10^2\lesssim \stackrel{\sim }{Ra}\lesssim 10^5\right)$, a correlation that is consistent with inferences made in prior studies. We further explore the nature of this correlation and its implications for geophysical and astrophysical systems.