Until very recently, the inversion of geomagnetic field models for core
surface flows has been treated as a purely kinematic problem, using the
core surface radial field as a passive tracer for the flow. We will
review this classical approach and its main results. Recent satellite
missions boosted an increasing complexity of computed magnetic-field
models, where the separation of different contributing sources seems
more and more realistic. Unfortunately we still have a blurred view of
the magnetic field at the core-mantle boundary. This is an important
issue as core flows are detected from the motion of magnetic flux lines
leaving the Earth’s core. We will discuss the strategies that have been
developped to fully account for this difficulty.
In an effort to use recent geomagnetic models to explore the Earth’s
core dynamics, we have been testing geostrophic/quasi-geostrophic flows.
To sustain the relevancy of these flows, we will argue that motions
evolving on timescales shorter than the magnetic diffusion time are
almost quasi-geostrophic and thus axially invariant: they are completely
determined from a stream-function, which is independent of the z-coordinate
along the rotation axis. We will then report how a planetary-scale
anticyclonic gyre has been inferred within the Earth’s fluid core.
It is likely that magnetic fields are much stronger inside the core that
at the core surface. The detection of a 6-yr periodicity in calculated
core flows may be the signature of Alfvén waves propagating inside the
core. That gives us an estimate of the magnetic-field intensity. We will
introduce the data assimilation scheme that we are now using to further
constrain the geometry of the magnetic field in the core interior.
Mot-clés : Champ magnétique, planète, Terre, géodynamique, géomagnétisme, noyau terrestre
Cursus :
Dominique Jault est chercheur au CNRS. Il mène des recherches sur l’origine et les variations du champ magnétique de la Terre.
Cliquer ICI pour fermerDernière mise à jour : 04/10/2013
Tous droits réservés
@ 2011 ENS