Planetary Science Seminar fall-2015

Characterizing convection in geophysical dynamo systems

The Earth's magnetic field is produced by a fluid dynamo in the molten iron outer core. This geodynamo is driven by fluid motions induced by thermal and chemical convection and strongly influenced by rotational and magnetic field effects. While frequent observations are made of the morphology and time-dependent field behavior, flow dynamics in the core are all but inaccessible to direct measurement. Thus, forward models are essential for exploring the relationship between the geomagnetic field and its underlying fluid physics.

In this talk, I will discuss a suite of nonrotating and rotating convection laboratory experiments reaching more extreme values of the governing parameters than previously possible. My experiments show that the regimes where numerical models produce Earth-like magnetic fields dwindle as more geophysical values of the governing parameters are achieved. Instead, comparison with numerical results indicates that regimes characterized by geostrophic turbulence are more likely to apply to the Earth’s core.

I will also discuss a theoretical analysis of results from a suite of dynamo simulations by Christensen and Aubert (2006). These results are broadly used in the geophysics community for describing the heat transfer, magnetic field, and velocity scaling properties in planets and stars. However, I find that the scaling laws derived from these simulations are fully dependent on the fluid viscosity, and therefore are unlikely to reflect the fluid physics driving dynamo action in the core. My findings reinforce the need to understand the turbulent flows underlying the geodynamo.