16th GFD Online Semiar (with Fluid Dynamics Seminar at RIMS, Kyoto Univ.)

• Date and plance:

  October 15, 2024, 15:00 - 16:30

  Zoom or Room 006 at Reearch Institute for Mathematical Sciences, Kyoto University

• Speaker and Title:

  Prof. Andrew Jackson (Institut für Geophysik, ETH Zürich, Switzerland)

  "Theory of the geodynamo: a century of struggle and a new dawn"

• Abstract:

  Earth's magnetic field is generated by fluid motion in the outer core by a process termed self-exciting dynamo action. In this process, electrically conducting fluid flows through a magnetic field, inducing electrical currents that reinforce the original magnetic field. The driving force for this is thought to be thermal convection.

  This process can be simulated on the computer in a self-consistent way, albeit in a parameter regime that is somewhat distant from planetary settings. In particular, the values of viscosity used are too large, and the prospects for reducing these viscosities to more appropriate values are remote. Despite this, the approach has met with great success and has demonstrated that magnetic fields can be generated in this way. Many features are quite Earth-like, most likely because the magnetic Reynolds number (the ratio of magnetic induction to magnetic diffusion) is in the correct regime. We will contrast conventional models with a different approach in which both inertia and viscosity are omitted from the equations at the outset. This approach, whilst in its infancy, holds the promise of providing complementary models of planetary magnetic field generation.