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Satellite geomagnetic data reveal interannual magneto-Coriolis waves inside Earth’s core

Authors

Gillet,  Nicolas
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Gerick,  Felix
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Jault,  Dominique
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Schwaiger,  Tobias
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Istas,  Mathieu
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Aubert,  Julien
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

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Citation

Gillet, N., Gerick, F., Jault, D., Schwaiger, T., Istas, M., Aubert, J. (2023): Satellite geomagnetic data reveal interannual magneto-Coriolis waves inside Earth’s core, XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) (Berlin 2023).
https://doi.org/10.57757/IUGG23-0506


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5015924
Abstract
We now benefit of more than two decades of global geomagnetic surveys from low-Earth orbiting satellites. They have revealed repeated interannual changes, more intense towards the equator. In order to reconstruct the dynamics at the surface of the core, these observational constraints are introduced in the “pygeodyn” data assimilation tool. This algorithm incorporates spatio-temporal constraints derived from geodynamo numerical simulations approaching Earth’s conditions. We discovered recurrent non-axisymmetric flow patterns presenting a period of about 7 yr. They propagate equatorward throughout the fluid core, and present their strongest amplitude (~3 km/yr) at the equator, where they show a coherent westward drift at phase speeds of about 1,500 km/yr. We interpret and model these flows as the signature of Magneto-Coriolis waves. Using synthetic data from dynamo simulations, we show that the recovery of such transient motions depends mostly on the data coverage and on their magnitude. The identification of Magneto-Coriolis waves offers a way to probe the cylindrical radial component of the dynamo field inside Earth’s core, and possibly to sample lateral variations in the electrical conductivity of the lower mantle. It follows from our work that there is no need for a stratified layer at the top of the core to account for these geomagnetic field changes. Such waves most likely also exist on longer time-scales, calling for long-lived magnetic records from space.