Laboratory experiments on rain-driven convection: Implications for planetary dynamos

• Published in: Earth and planetary science letters Vol. 457; pp. 403 - 411
• Main Authors: Olson, Peter, Landeau, Maylis, Hirsh, Benjamin H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2017; Elsevier
• Subjects: Astrophysics; Convection; convection experiments; Earth and Planetary Astrophysics; Fluid dynamics; Fluid flow; Fluids; iron snow; magnesium precipitation; Nonlinear Sciences; planetary dynamos; Rain; rain-driven convection; Rotating generators; scaling laws; Sciences of the Universe; Turbulence; Turbulent flow; scaling laws; iron snow; rain-driven convection; planetary dynamos; convection experiments; magnesium precipitation; Rain-driven convection
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2016.10.015

Compositional convection driven by precipitating solids or immiscible liquids has been invoked as a dynamo mechanism in planets and satellites throughout the solar system, including Mercury, Ganymede, and the Earth. Here we report laboratory experiments on turbulent rain-driven convection, analogs for the flows generated by precipitation within planetary fluid interiors. We subject a two-layer fluid to a uniform intensity rainfall, in which the rain is immiscible in the upper layer and miscible in the lower layer. Rain falls through the upper layer and accumulates as a two-fluid emulsion in the interfacial region between the layers. In experiments where the rain is denser than the lower fluid, rain-injected vortices evolve into small-scale plumes that rapidly coalesce into larger structures, resulting in turbulent convection throughout the lower layer. The turbulent convective velocity in our experiments increases approximately as the cube root of the rain buoyancy flux, implying little or no dependence on viscous and chemical diffusivities. Applying diffusion-free scaling laws for magnetic field generation, we find that precipitation-driven convection can be an effective dynamo mechanism in planetary cores provided the precipitation buoyancy flux is large and the convecting region is deep and nearly adiabatic. •We present experiments on convection driven by rainfall.•Turbulent rain-driven convection exhibits inertial scaling.•Intense precipitation can be an effective dynamo mechanism.