Geomagnetism
Observing, modelling and predicting the Earth’s magnetic field
From the archives (in French): the group in 2010
In all space, around and inside the Earth, there is a magnetic field. This field is close to a dipole slightly inclined with respect to the axis of rotation of the Earth. Several phenomena sum up and constitute the total magnetic field, which varies constantly according to the variations of the sources which generate it. Its study allows us to understand the structure and the internal dynamics of the Earth as well as the phenomena that occur in the upper atmosphere and in space. Observations of this field, either by satellites or by measurements made in observatories, and numerical models allow us to constrain the physical processes that come into play.
Observations of the magnetic field and the ionospheric environment
The group collaborates with the magnetic observatories of the IPGP and operates space missions, such as the ESA Swarm constellation, whose absolute magnetometers (developed by CEA-Leti, funded by CNES), are under its responsibility. It is at the origin of the NanoMagSat project under development in the framework of the ESA Scout program. This constellation aims to develop permanent space observation of the magnetic field and the ionospheric environment, thanks to nanosatellites.
Interpreting and predicting
The interpretation of magnetic data from satellites or ground-based observatories requires the separation of the contributions from the different sources generating the magnetic field. The signals associated with the internal sources of the Earth, such as the lithosphere, are studied in detail within the team. Particular attention is paid to the core field, its temporal evolution and its prediction. External sources, such as the ionosphere and the magnetosphere, have also become important topics recently.
Numerical dynamo simulations
This part of our activities is based on massively parallel codes developed by the researchers of the group, whose expertise allows to combine flexibility and innovation. Our most recent studies concern the effect of a stably-stratified layer on the convective flow and the dynamo (for Earth and Jupiter), double-diffusive convection, and dynamo action in a full fluid sphere, relevant for Earth prior to the nucleation of the inner core.
Geomagnetic field and Earth's rotation
On geological time scales:
– The axis of the magnetic dipole coincides with the rotation axis
– By conservation of angular momentum, the redistribution of the mantle masses by convection generates a global rotation of the planet with respect to its rotation axis. This is the True Polar Wander.
