Core Dynamics and Geodynamo Simulations

In order to learn more about the deep Earth, computational models describing the relevant underlying physics must developed and their predictions compared with geophysical observations. Due to the extreme physical conditions in the deep Earth approximations are required, and there is a need for developing reduced models where parameter space can be more fully explored. I am interested in new computational methods for core dynamics, and the combination of such models with observations through the techniques of data assimilation.

  • As part of the ERC funded CoreSat project, I am working with Olivier Barrois (DTU Space), Thomas Gastine (IPGP),  Nicolas Gillet and Nathanel Schaeffer (IsTerre, Grenoble) on a new QG magneto-convection code suitable for studying the action of rotation-dominated convection in the presence of a 3D magnetic field. A particular focus is on the role of large scale eddies in producing weak field regions at the core-mantle boundary.

Example of quasi-geostrophic rotating convection in a spherical shell at low Ekman number (10^-6) and low Prandtl number (10^-2).  Axial vorticity is contoured:

  • I have worked with Andrey Sheyko and Andy Jackson (ETH Zurich) on low viscosity numerical dynamos in which the dissipation occurs primarily Ohmically, as is relevant for the Earth's core.  We have investigated reversal mechanisms, the role of the magnetic field in the flow dynamics when magnetic forces are strong, and the importance of the tangent cylinder region for dissipation processes.

An example snapshot of the radial magnetic field at the core-mantle boundary from a low Ekman number (10^-6),  numerical dynamo simulation

Sheyko, A., Finlay, C.C. and Jackson A. (2016) Magnetic reversals from planetary dynamo waves, Nature, 539, 551–554, doi:10.1038/nature19842
Reversal movie on youtube

Sheyko, A., Finlay, C.C., Favre, J., and Jackson, A. (2018) Scale separated low viscosity dynamos and dissipation within the Earth’s core, Scientific Reports, Vol 8, 12566, DOI:10.1038/s41598-018-30864-1

  • In collaboration with Julien Aubert (IPGP) I have worked on self-consistent dynamical mechanisms in geodynamo models capable of reproducing important aspects of observed secular variation, in particular the westward drift, dipole decay and most recently geomagnetic jerks.

I am also working with Nicolas Gillet (IsTerre, Grenoble) and Olivier Barrois (DTU Space) on combining statistics from such simulations with satellite and ground observations via data assimilation methods.

Example: Visualization of the vorticity and magnetic field within the core obtained after assimilation of data from the COV-OBS field model with statistics derived from the Coupled-Earth dynamo:

 

Finlay, C.C., Aubert, J. and Gillet, N. (2016) Gyre-driven decay of the Earth's magnetic dipole, Nature Comm., Vol 7,  doi: 10.1038/ncomms10422

Barrois, O., Hammer, M.D., Finlay, C.C., Martin, Y., and Gillet, N. (2018) Assimilation of ground and satellite magnetic measurements: inference of core surface magnetic and velocity field changes, Geophys. J. Int, Vol 215, 695-712, doi:10.1093/gji/ggy297

Aubert, J., Finlay, C.C., Fournier, A. (2013) Bottom-up control of geomagnetic secular variation by the Earth's inner core, Nature, Vol 502, 219-223, doi:10.1038/nature12574. 

Aubert, J. and Finlay, C.C. (2019) Geomagnetic jerks and rapid hydromagnetic waves focusing at Earth’s core surface, Nature Geoscience, Vol 12, Issue 4, DOI:10.1038/s41561-019-0355-1


https://www.staff.dtu.dk/cfinl/research/core-dynamics-and-geodynamo-simulations
24 OCTOBER 2020