Rapid Dynamics in the Earth's Core

The problem of how the Earth generates its magnetic field is one of the outstanding scientific challenges of the present time. Observations and models of the geomagnetic field provide a window through which the dynamic processes and structure of the Earth's deep interior can be studied, a technique that complements seismic studies. In the last two decades, a variety of satellite missions have significantly improved our knowledge of the Earth's magnetic field, both in its spatial structure and in its temporal behaviour on decadal time-scales. Because these observations cannot probe deeper than the lower-most mantle, any understanding of the fluid outer core, where the field is generated, along with any insight into its time variability, must be obtained by from models.

Geodynamo models of the core have traditionally focused on millennial or longer time-scales to understand the long-term evolution of the field, for the most part ignoring the shorter time-scales. Our aim is to investigate these rapid dynamics which are of great scientific interest, being the very signal for which we have accurate observations. Such a project complements the vast scientific effort and expense being channelled into the latest generation of satellites.

We propose three interlinked yet independent projects which will be split between the Schools of Mathematics and Earth & Environment at the University of Leeds: (i) The construction of numerical models of the excitation and rapid dynamics in the core; (ii) The development of macrodynamic models of flow instabilities in the core; (iii) The extraction and modelling of flow accelerations in the core from observational satellite data.

Convection-driven spherical shell geodynamo simulations, which solve the fundamental equations from first principles, have been remarkably successful in explaining many features of the observed geomagnetic field, but they do suffer from some important limitations. Even with the most powerful computers, the models cannot resolve short length scales and timescales, and so have to be run with much larger viscous and thermal diffusion that occurs in the Earth's core.

In this project, simplified geometry models will be developed to examine the dynamics in the core at very small thermal and viscous diffusion. This will also enable us to investigate much shorter time-scale field variations on the 1-100 year time-scale, to discover what is causing these variations, and to compare our numerical simulations with observations.

This research will also help us to investigate the small length-scale behaviour in the core, on scales of 1-100 km, which is too computationally expensive to obtain by direct numerical simulation. By establishing what are the important force balances across the whole range of relevant scales in the core, the essential requirements for developing more realistic spherical shell dynamo models will be identified.