ISTerre - Institut des Sciences de la Terre

Projet AVS Geomag

Nicolas GILLET — 2025-09-05T13:50:29Z

Assimilation of geomagnetic observations in dynamical models of the Earth's core

Duration : 2011 - 2016

Coordinator : Alexandre Fournier (Institut de Physique du Globe de Paris), Nicolas Gillet (ISTerre)

ISTerre research team involved :
– Geodynamo

Collaborations :
– Institut de Physique du Globe de Paris

AVSGeomag is a research program supported by the Agence Nationale de la Recherche, which aims at developing tools to assimilate observations of the Earth's magnetic field into dynamical models of the Earth's core. The funding runs between September 2011 and September 2015.

– Web site of the project

ESA project '4D-Earth Core + SWARM'

Henri-Claude NATAF, Nicolas GILLET — 2020-07-13T09:25:25Z

- Completed projects

current post-doc proposals

2020-03-12T15:21:35Z

- Internships, PhD, post-doc offers

Quasigeostrophy

Dominique JAULT, Henri-Claude NATAF, Nicolas GILLET, Philippe CARDIN — 2019-10-15T13:22:06Z

We expect Earth rotation to make the motions in the core columnar, nearly invariant in the direction parallel to the rotation axis. Geodynamo simulations nicely reproduce this feature.

Assuming columnar geometry (quasi-geostrophic hypothesis), we find that the motions depend only on the spatial coordinates in a plane perpendicular to the rotation axis, making the problem two-dimensional and reducing its size significantly.

There is a large body of research on quasi-geostrophic flows that has been developed specifically to better understand motions in thin fluid layers (Earth atmosphere and oceans). We use this approximation to compute dynamical regimes of thermal convection instead in a rapidly rotating sphere.
We have been able to reproduce turbulent convection for very low viscosity and to exhibit a regime where the small diffusivities do not control the dynamics. Interestingly, in this new regime, we discover that thermal convection becomes subcritical and consequently shuts down abruptly, which could explain rapid extinction of some ancient planetary dynamos (Mars, Moon…).

We have also obtained a new set of reduced quasi-geostrophic momentum equations valid in deep shells, such as planetary cores, including their equatorial regions. We generalize these equations to non spherical bodies in order to document the pressure coupling between the fluid and its solid boundaries. We thus obtain very good approximations of the slowest inertial modes. We are also pairing the quasi-geostrophic equation with the induction equation (for the magnetic field) in order to model the secular variation of the Earth's magnetic field.

Geomagnetic data analysis

Dominique JAULT, Henri-Claude NATAF, Nicolas GILLET, Philippe CARDIN — 2019-09-14T13:37:05Z

The Swarm mission of ESA is today central to the efforts carried by the geomagnetic community. It will allow a better description of external magnetic fields, and thus open a window towards the dynamics in the core at interannual (to monthly ?) periods. This evolution occurs at the same time a new generation of geodynamo simulations arises. It is timely to combine the above two aspects through data assimilation studies. Because we only have access to a limited amount of geophysical constraints (the field at the core surface), this requires to develop reduced models able to reproduce the rapid dynamics in the core. This is the rationale under the development of magnetic quasi-geostrophic equations, or of stochastic models anchored to geodynamo statistics.

Our efforts are supported by the Centre National d'Etudes Spatiales (CNES). In this context, we propose several products to the community:

– the geomagnetic data assimilation tool pygeodyn;

– the web platform webgeodyn for core surface flow and magnetic field visualization;

– the magnetic field model COV-OBS that covers eras of observatory and satellites magnetic records (1840-2020, coll. DTU Space, Copenhagen).

webgeodyn

Nicolas GILLET — 2019-09-14T13:33:47Z

a visualization tool for flows and magnetic field at the Earth's core surface

https://geodyn.univ-grenoble-alpes.fr/

View online : https://geodyn.univ-grenoble-alpes.fr/

pygeodyn

Nicolas GILLET — 2019-09-14T13:33:17Z

a data assimilation tool that proposes re-analyses of the flow and magnetic field at the Earth's core surface, based on a stochastic model plugged into an ensemble Kalman filter

https://gricad-gitlab.univ-grenoble-alpes.fr/Geodynamo/pygeodyn

- Simulation softwares

Former team members

Henri-Claude NATAF, Nicolas GILLET, Philippe CARDIN — 2019-08-26T15:31:29Z

– Guillaume Morard (Chargé de Recherche CNRS 2019-2023) is now in Institut de minéralogie, de physique des matériaux et de cosmochimie in Paris.
Guillaume Morard sur ResearchGate

– Mathieu Istas (Ingénieur de Recherche CNRS, CDD CNES 2020-2023). Membre du Service Geodata d'ISTerre. En charge du développement des outils pygeodyn et webgeodyn. Maintenant Ingénieur de Recherche CNRS à l'Institut Néel.
Mathieu Istas sur Linkedin

– Loïc Huder (Ingénieur d'Etudes CNRS, CDD CNES 2018-2020). Membre du Service Geodata d'ISTerre. En charge du développement des outils pygeodyn et webgeodyn. Maintenant Ingénieur à l'ESRF.
Loïc Huder sur GitHub

– Adeline Richard (Ingénieure d'Etudes CNRS 2008-2017) à mi-temps dans l'équipe géodynamo. Maintenant affectée au Laboratoire de Physique Subatomique et Cosmologie.

– Patrick La Rizza (Ingénieur d'Etude CNRS 2006-2016). Ingénieur électronicien. Retraité.

– Jean-Paul Masson (Ingénieur de Recherche CNRS 1999-2016). Ingénieur mécanicien. Cristal du CNRS en 2005. Retraité.
Quelques archives de J-P. Masson

– Denys Schmitt (directeur de recherche CNRS, 2005-2012). Retraité en octobre 2012, puis décédé en août 2015. Liste de publications et journée scientifique organisée en son hommage.

– Thierry Alboussière (2003 - 2009) Checheur CNRS dans l'équipe. Actuellement directeur de recherche au laboratoire de Géologie de Lyon.

– Alexandre Fournier (2004-2008) maitre de conférence à l'université Joseph Fourier et chercheur dans l'équipe. Actuellement professeur à l'Institut de Physique du Globe de Paris.

– Daniel Brito, (1998-2008) maitre de conférence à l'université Joseph Fourier et chercheur dans l'équipe. Actuellement, professeur à l'université de Pau.

Former post-docs

Henri-Claude NATAF, Nicolas GILLET, Philippe CARDIN — 2019-08-26T15:31:18Z

– Hannah Rogers

– Kang Wei Lim

– Ludovic Huguet

– Tobias Schwaiger (postdoc CNES xx-2022)

– Manohar Kumar Sharma

– Long Chen

– Jenny Wong (postdoc 2019-2021) : dans le cadre du projet ERC SEIC (Setting Earth's Initial Conditions) de Renaud Deguen.

– Elliot Kaplan (postdoc CNRS 2015-2016) : simulations numériques DTS et convection, dans le cadre de l'ANR TuDy.

– Aldo Figueroa (postdoc CNRS en 2011-2012), Modes and instabilities in magnetized spherical Couette flow, enseignant chercheur au Mexique.

– Céline Eymin

– Douglas Mac Lean

Former visitors and guests

Henri-Claude NATAF, Nicolas GILLET, Philippe CARDIN — 2019-08-26T15:31:10Z

Yue-Kin Tsang, University of Newcastle, April 2025 : time-scales of magnetic secular variation and double diffusive convection.

Mohamed Hamoudi Janvier 2020, janvier 2022 : champ magnétique lunaire et cartographie globale du champ crustal de la Terre.

Zahia Tigrine (2017, 2018) : ondes d'Alfvén et ondes d'Alfvén géostrophiques, dans le cadre de l'ANR TuDy.

Mathieu Dumberry Professeur invité à l'université Joseph Fourier en 2015 (8 mois), professeur à l'université d'Alberta (Edmonton - Canada).

Santiago Triana.

Dan Lathrop.

Mickael Purucker professeur invité en 2012 (2 mois). Chercheur au Goddard Space Flight Center, NASA, Greenbelt, Maryland, USA.

Rodion Stepanov (chercheur invité 2 mois en 2011, nombreux séjours en 2008, 2009, 2012, 2014, 2019), chercheur à l'Institute of Continuous Media Mechanics of the Russian Academy of Science, Perm, Russie.

Wenya Xu

Chris Jones

Jonathan Aurnou

Keith Aldridge

Fritz Busse

Jon Rotvig

Graeme Sarson

Agris Gailitis