par- 9 janvier 2014
Geomagnetic records give us the main information source to probe the dynamics in the liquid core of our planet. Continuous magnetic measurements from low-orbiting satellites, from 1999 onwards, have already brought a new vision of our magnetic lanet. The community has been in particular puzzled by the fast changes occurring at all length-scales. Separation of the different sources (core, lithospheric and atmospheric) now constitutes the main limitation to our understanding of the observed rapid magnetic variations. The Swarm mission of ESA, with its three spacecrafts simultaneously probing the magnetic field, will allow better dissociating signals from ionospheric, magnetospheric and core regions. There is thus a chance to detect rapid phenomena occurring in the Earth’s core never (« Rossby waves ») or poorly (« torsional waves ») imaged so far. The physics of these waves is consistent with the observation that rapidly evolving large length-scale motions are favoured in the presence of global rotation.
Planetary scale motions are the very motions that can be inferred from geomagnetic data. To be concrete, the PhD candidate will calculate the co-evolution of magnetic and velocity fields, using a minimal model where unresolved or unknown forces entering the governing equations are represented by stochastic processes. Following this avenue, she/he will provide a full probability distribution of the core state, which allows giving uncertainties on the proposed field evolution, as commonly done in meteorological studies. The PhD thesis will follow successive steps : a) build a time-dependent stochastic forward and inverse computer model that monitors the evolution of the core surface flow and magnetic field ; b) test its ability to predict the field evolution against already existing magnetic data ; c) estimate which part of the high frequency magnetic variability enters respectively the core and atmospheric sources.
The young scientist will have to face issues in applied maths and computing sciences, together with the confrontation to geophysical data. She/he will build up on studies previously carried out within the "geodynamo" team of ISTerre [1,2]. This project will lead to discussions with colleagues at the DTU Copenhagen, with whom we collaborate in the framework of a project recognized by ESA ("Swarm Science and Validation Opportunity").
 Gillet, Jault, Canet & Fournier (2010), Nature, 465 (7294), 74-77.
 Gillet, Jault, Finlay & Olsen (2013), G-cubed
contacts : email@example.com ; firstname.lastname@example.org
pour candidater : lien vers le site du CNES, rubrique "Sciences utilisatrices des moyens spatiaux" (SUMS)
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