Institute of Geophysics and Tectonics (IGT) PhD Projects
Oscillations in the Earth’s core
Supervisors: Dr Phil Livermore & Dr Jon Mound
A proper understanding of how the geomagnetic field is generated in Earth’s liquid core remains one of the greatest outstanding problems in Earth science. The principal difficulty is that the core is far too remote to be probed directly; scientific knowledge has advanced through exploiting the limited set of observations and computer simulations of the Earth’s core. These models, much like those used to simulate weather or climate, have improved significantly in the last few decades, largely due to the recent technological improvements in computing.
Scientific attention has generally been focused on models of the geodynamo, the mechanism responsible for generating the Earth’s field, over millennia or longer timescales. Such studies have greatly improved our understanding of the long-term variations in the Earth’s field, including suggesting plausible causes of global magnetic reversals. However, a comparison of these models to the real geomagnetic field is extremely difficult. The key problem is that detailed observations of the field stemming from fixed observatories, shipping logs and more recently from orbiting satellites, only span a few centuries and describe dynamics much too rapid to be properly resolved in the models. These observations highlight some interesting and fundamental dynamics, of which one of the most important is the realization that the outer-core fluid oscillates on concentric cylinders (see figure). These so-called torsional oscillations, occurring over a timescale of 1-10 years, not only drag magnetic fields around (in a manner that can be observed) but also influence the length of day (due to conservation of angular momentum, for example, if the core fluid rotates faster on average, the mantle must rotate more slowly and the length of day increases).
Despite strong observational evidence for their existence, torsional waves have been identified in only a few geodynamo models and even then not conclusively. The central problem is that the model parameters are generally selected for investigating timescales much longer than decades, and thus any resulting torsional oscillations are not well resolved.
The student will modify and use existing computer code in order to run geodynamo models over decadal timescales. Making a further additional assumption of axisymmetry, leaving unchanged the dynamics of torsional oscillations, may further provide access to realistic model parameters. This approach allows a much more accurate treatment of shorter-term dynamics and the resulting simulations, along with comparison to observational data, will provide great insight into how torsional oscillations arise and how they propagate. This project makes the link between the sometimes quite disparate research areas of computer modeling and geomagnetic observations and is of potentially great interest to the worldwide scientific community.
The student will require a strong background in mathematics/physics/computing and an interest in learning high-performance computing. Although based principally at Leeds, there will be significant opportunity for travel. It is anticipated that, in addition to national meetings, the student will attend an international conference such as the fall AGU meeting in San Francisco. Furthermore, there is scope for visits abroad to work with existing collaborators of the supervisors, including those in Switzerland and California.