A NEW HOPE: CAN WE PREDICT GEODYNAMO DYNAMICS?

Abstract

The Earth’s magnetic field is hugely important, as it protects the surface of the planet from cosmic radiation and charged particles coming from the Sun and enables navigation for many living species. However, how it is generated and why it changes its value and configuration in time is poorly understood. The leading theory for the generation of the Earth’s magnetic field is the geodynamo: an electrically conductive fluid in the Earth’s core creates and maintains a magnetic field over an astronomical time scale.To probe this theory experimentally, the Three Meter Experiment—a 3 meter diameter spherical-Couette apparatus—was built to model the Earth's core. The experiment consists of two rotating concentric spheres with liquid sodium between them. The rotating spheres generate fluid motion and reproduce the dynamics similar to those that occur in the planet's core. The previous generation of the experiment was not able to generate a self-sustaining magnetic field. However, numerical studies suggest that increasing the roughness of the liquid to the solid boundary should allow enable entering the dynamo regime. To test this, we first built a scaled-down model of the Three Meter sodium experiment. This was a 40-cm water experiment to examine the increase in helicity of the flow from installing baffles on the inner sphere. We then drained 12 tons of liquid sodium from the Three Meter experiment, cleaned, fixed, and upgraded it with baffles to increase surface roughness. We then re-filled the Three Meter experiment with sodium and performed several experiments. Here, we present the results of studying the torque scaling in the experiment. We show that the experiment's highest Reynolds number is limited by the maximum torque and power in the driving motors. We further investigate the magnetic data from various experiments and show that we are likely on the edge of the dynamo action. We present observation of traveling magneto-Coriolis modes and analyze their dynamics in different conditions. These structures are important for understanding some changes in celestial objects' magnetic fields and their mechanical properties. We also present a software tool developed to mimic the observed behavior of this magnetohydrodynamic experiment. This gives us a proper tool to predict the near future of dynamos, and allows us take a deeper look into its internal structure.