The Role of Large-Scale Shear Flows in the Geodynamo

Full details with project descriptions - and how to apply at: http://www.maths.leeds.ac.uk/postgraduate-research.html

One of the outstanding problems in geosciences is to understand the Earth’s magnetic field. It is universally accepted that the magnetic field is maintained by some sort of dynamo process, involving the motion of the liquid iron in the outer core. However, precisely what is going on remains a fascinating research question.

Paleomagnetism has revealed that the Earth’s magnetic field has long periods, of the order of millions of years, in which it has one sign, but that it can then reverse sign over a relatively short period. It has thus been suggested that the dynamo operates close to the boundary in parameter space separating dipolar from multi-polar solutions. This project will seek to explore this issue through an investigation of the role in the dynamo process of the interaction between small-scale convective flows and a large-scale shear flow. It will employ certain simplifications, particularly in the geometry, and will thus be complementary to global computational studies of the geodynamo.

The project will first look at the role of a large-scale shear flow on small-scale dynamo action resulting from an idealized forced cellular flow of the type found in rapidly rotating environments such as the Earth's outer core, seeking to determine the boundary between small- and large-scale dynamo action. The model will then be extended to model strongly rotating convective flows more realistically, via cellular flows with a well-defined (long) correlation time that can be set as a variable parameter, and will incorporate shear flows of the type found in the Earth's interior.

The project will train the student not only in the geodynamo and in theoretical fluid dynamics and magnetohydrodynamics, but will also provide valuable analytical and computational skills.