Institute of Geophysics and Tectonics (IGT) PhD Projects
Sudden Accelerations in the Flow of the Earth’s Core
Supervisors: Dr Phil Livermore & Dr Jon Mound
This studentship is fully-funded by a NERC grant which will pay the UK research council level stipend and fees, and research training and support grant/conference funding. NERC funding eligibility restrictions apply – for further details visit www.nerc.ac.uk/funding/available/postgrad/eligibility.asp.
Application deadline: 15 March 2011
The magnetic field of the Earth is generated in the fluid core, and flow in the core causes the magnetic field to evolve through time. Therefore, the observed changes in the magnetic field can be used to probe flow at the surface of the core. Data from satellite missions, supplemented with observatory data, have provided improved spatial and temporal resolution of core flow and led to the discovery of rapid flow accelerations that appear to correlate with geomagnetic jerks (step changes in the second derivative of geomagnetic variation). Core flow inversions from magnetic field observations require the adoption of some simplifying assumption regarding the dynamics of the flow (e.g. steady, steady plus torsional oscillations, tangentially geostrophic) in order to reduce the degrees of freedom and make the problem solvable.
Figure 1: Magnetic declination at the Earth’s surface from the latest IGRF model (Finlay et al. 2010). Changes in the magnetic field through time are used to map flow at the surface of the fluid core.
Previous work has investigated the nature of flow accelerations that occur at the times of geomagnetic jerks and the initial stages of the studentship will further investigate the range of flows that are compatible with the observed magnetic field variations at these times. The suite of core flow inversions will then be used to calculate the associated torques on the core-mantle boundary. Electromagnetic coupling between the core and mantle has been shown to play an important role in the dynamics of torsional oscillations and the student will expand the existing coupling theory to include non-zonal flows. Initial calculations will use simplified (low order) descriptions of both the flow and the magnetic field, with added complexity gradually built in until the torque is calculated for the observed field and flow. Starting from a simplified model will enable us to investigate the dependence of the torque on the length scale of both the field and flow, and thus estimate the magnitude of the torques that might be generated by unobservable higher order components. By explicitly calculating the torque on the mantle it will be possible to test whether the inverted flows can produce the changes in Earth rotation that are required to explain the observed correlations of geomagnetic jerks with variations in length-of-day and the Chandler wobble.
This studentship is part of a NERC project on the rapid dynamics of the Earth’s fluid core. This studentship will focus on observational evidence of sudden accelerations in core flow and their affect on the rotation of the Earth. Parallel projects at Leeds in both the School of Earth and Environment and the Department of Applied Mathematics will be developing new approaches to numerical modelling of core flow.