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Improved mapping of Earth's internal magnetic field from space

Dr Phil Livermore (SEE), Dr Chris Davies (SEE), Dr William Brown (British Geological Survey), Dr Ciaran Beggan (British Geological Survey)

Project partner(s): British Geological Survey (CASE)

Contact email: p.w.livermore@leeds.ac.uk

Background

Observations of Earth’s magnetic field, both from the ground and from space, provide information on processes inside the Earth’s core all the way to the near-Earth environment in which spacecraft operate, and provides us with a means to navigate above and below Earth’s surface. To create a map of the internally generated field, measurements of the magnetic field must be compiled into a geomagnetic field model, whose accuracy is crucial in making scientific inferences about the Earth’s interior. These models describe the shape and strength of the geomagnetic field, and its variations in space and time. Data for these models currently come from ground observatories and the ongoing European Space Agency (ESA) Swarm satellite mission.

Figure 1 Earth's internal magnetic field as described by a geomagnetic field model. The magnetic field generated inside the liquid core (colours represent strength and direction) extends up to the Earth’s surface and into space.

Field models can generally be categorised into those that are focussed on modelling a single field source such as the outer core or the crustal rocks, or those which model a “comprehensive” range of field sources which are solved for simultaneously. A challenge in geomagnetic modelling is to separate the various sources of the field. Field generated in the core, lithosphere, ionosphere, magnetosphere and oceans, manifest and vary on overlapping time and space scales. The greatest challenges are at high latitudes, where the Sun strongly influences magnetic activity. Ionospheric currents known as the auroral electrojets generate a time-varying field that is often unsatisfactorily resolved in models, and masks other field sources from being well resolved.

Figure 2 Typical misfit to satellite observations from a geomagnetic field model. The largest errors are near the poles at 60-90 degrees latitude.

Recent advances in computational power and highly parallelised algorithms have allowed us to move from isolating single sources from carefully selected magnetic field data to treating more data with the aim of identifying multiple sources simultaneously. Current procedures can reject 99% of satellite and ground data, and are often most drastic in the auroral and polar regions, which contributes to poor model performance in these areas.

This project is focussed on improving the modelling capability at high-latitude, which will result in a step-change in our ability to fit globally the available data.  A key tool for the project is the availability of a sophisticated, scalable, geomagnetic field modelling code suitable for high performance computing, developed through the Model of Earth Magnetic Environment (MEME) project, in conjunction with Edinburgh Parallel Computing Centre (EPCC). Using high-performance computing will allow rapid creation of field models, for the first time making it feasible to test and evaluate different methods of modelling high-latitude magnetic fields.

This PhD project will focus on the following:

  1. Porting the EPCC code to the Leeds High-Performance Computing (ARC) facility and investigating the use of wider selections of ground observatory and satellite data to improve the core and crustal field models
  2. Developing improved representations of magnetic fields at high-latitudes, along with other sources of magnetic field.
  3. Investigating data selection procedures that can enhance such models, with a view to utilising more of the available data, particularly at high latitudes and magnetically disturbed times.

The aim is to expand upon the complexity of the modelled field, include more field sources, and investigate ways in which data can be utilised more effectively to characterise the Earth’s field.

Objectives

  1. To assess the existing and desirable capabilities of geomagnetic field models and ascertain which field sources to model, then suitably adapting the BGS MEME modelling code
  2. To investigate the use of recent developments in geomagnetic activity measures and specific models of high-latitude external field sources from the ESA Swarm mission
  3. To develop new criteria to select satellite and ground data to more effectively model the internal field behaviour.
  4. To use these new models of the internal geomagnetic field to investigate rapid dynamics within the Earth’s liquid core, such as waves and jets.

Milestones

Year 1:  Familiarisation with geomagnetic field modelling and the BGS MEME code, and expansion of the geomagnetic sources modelled. Porting of code to ARC (or another HPC)

Year 2:  Improved modelling at high-latitude and data selection criteria, taking advantage of latest developments from ESA Swarm mission, including field gradient information

Year 3: Production of an enhanced geomagnetic field model, focussing on high latitude regions and  more accurate separation of field sources. Using the new geomagnetic field model, investigate proposed phenomena of waves and jets within the Earth’s core.

Potential for high impact outcome

Field models are heavily used in a wide range of academic and applied studies, and the number of research groups actively maintaining them is small. Improved modelling of high-latitude regions would produce a step-change in the research area and would have an international impact.

Training

The student will learn both the theory and computational techniques required to model the geomagnetic field, and will have access to a broad spectrum of training workshops put on by the Faculty that include an extensive range of workshops in numerical modelling, high-performance computing, through to managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/).

The student will be a part of the deep Earth research group, a vibrant part of the Institute of Geophysics and Tectonics, comprising staff members, postdocs and PhD students. The deep Earth group has a strong portfolio of international collaborators which the student will benefit from.

Although the project will be based at Leeds, there will be opportunities to attend international conferences (UK, Europe, US and elsewhere), and collaborative visits within Europe.  The project will involve multiple visits to BGS in Edinburgh.

Requirements

We seek a highly motivated candidate with a strong background in mathematics, physics, computation, geophysics or another highly numerate discipline.

References

Olsen, N. and C. Stolle (2012). Satellite Geomagnetism, Annu. Rev. Earth Planet. Sci. 2012. 40:441–65. DOI 10.1146/annurev-earth-042711-105540

Hamilton, B., Ridley, V. A., Beggan, C. D., & Macmillan, S. (2015). The BGS magnetic field candidate models for the 12th generation IGRF. Earth, Planets and Space, 67(1), 69.

Kauristie, K., Morschhauser, A., Olsen, N., Finlay, C. C., McPherron, R. L., Gjerloev, J. W., & Opgenoorth, H. J. (2017). On the usage of geomagnetic indices for data selection in internal field modelling. Space Science Reviews, 206(1-4), 61-90.

Sabaka, T. J., Olsen, N., Tyler, R. H., & Kuvshinov, A. (2015). CM5, a pre-Swarm comprehensive geomagnetic field model derived from over 12 yr of CHAMP, Ørsted, SAC-C and observatory data. Geophysical Journal International, 200(3), 1596-1626.

Aakjaer, C. D., N. Olsen, and C. C. Finlay (2016), Determining polar ionospheric electrojet currents from Swarm satellite constellation magnetic data, Earth Planets Space, 68, 140, doi:10.1186/s40623-016-0509-y.

Related undergraduate subjects:

  • Applied mathematics
  • Computer science
  • Computing
  • Earth science
  • Geophysical science
  • Geophysics
  • Mathematics
  • Physical science
  • Physics
  • Remote sensing