Liquid Sodium Models of the Earth's Core

Department of Mechanical Engineering & Materials Science Seminar

Liquid Sodium Models of the Earth's Core

Professor Daniel P. Lathrop
Professor of Physics & of Geology
University of Maryland, College Park

By using liquid sodium models of the Earth's core, we hope to better understand what determines the Earth's magnetic field strength, pattern and dynamics by probing the effects of turbulence, Lorentz forces and rotation on core dynamics. While it is not possible to match every aspect of core dynamics in the laboratory, the experiments described in this talk seek a comparable force balance among rotation, magnetic fields and advection.

We present new experimental results from the University of Maryland Three-Meter diameter Geodynamo experiment. We drive a fully turbulent flow in water and also in sodium at magnetic Reynolds number up to Rm =900 in a spherical Couette apparatus geometrically similar to Earth's core. We have not yet observed a self-generating dynamo, but we study MHD effects with an externally applied axisymmetric magnetic field. We survey a broad range of Rossby number −68 < Ro = ∆Ω/Ωo < 65 in both purely hydrodynamic water experiments and sodium experiments with weak, nearly passive applied field. We characterize angular momentum transport and substantial generation of internal toroidal magnetic field (the Ω-effect) as a function of Ro and find a rich dependence of both angular momentum transport and Ω-effect on Ro. Internal azimuthal field generation peaks at Ro = 6 with a gain as high as 9 with weak applied field. We observe intermittent dipole gain in some states that must come from non-axisymmetric flow and seems to be a geodynamo-style feedback involving differential rotation and large-scale drifting waves.

Wednesday, October 5, 2016
2:30 – 3:30 pm
Location – Mason 107
Host: Professor Judy Cha
Refreshments served at 2:15 pm