"Has the Earth's magnetic field periodically collapsed since its last reversal, 780.000 ago?"
Résumé
" Has the Earth's magnetic field periodically collapsed since its last reversal, 780.000 ago? " Invited speaker: Saracco Ginette ; Lieu: Institut de Mathematiques d'Orsay, France, 12-14/06/2019 ; Authors: Nicolas, Thouveny, Didier Bourles, Quentin Simon, Ginette Saracco ; Address: CNRS-UMR7330, CEREGE, AMU, CdF, IRD, INRA,Europole de l'Arbois, Aix-en-Provence, France ; Abstract : The hypothetical contribution of the Earth’s axis precession to the geodynamo energy was recently reinforced by experimental and numerical geodynamo models, triggering new research on the possible influence of orbital periodicities, e.g. axial precession (≈26.000 years) and obliquity (≈42.000 years) in the paleomagnetic field spectrum (e.g. Thouveny et al. 2008; Saracco et al. 2009). Oceanic sedimentary sequences contain records of geomagnetic paleointensity, as well as cosmogenic nuclide production records, that provide some appropriate time-series of the geomagnetic dipole moment variations, allowing us to extract all frequency modulation laws of it, from algorithms based on the phase of a linear time-frequency method as the complex wavelet transform. Beyond the fundamental interest for mechanical constraints on the geodynamo, the interest of such studies lies in the fact that, at present and for the last 3 millennia, the dipole moment has been decaying by about 30% (from 11.5 10^22 A.m^2 to less than 8 10^22 A.m^2 ), either a rate equivalent to that leading to the full cancellation of the dipole at the time of excursions and reversals of the geomagnetic field. Since the last excursion (LASCHAMP) occurred 41.500 years ago, i.e. about for one obliquity period, solving the question raised, here, takes all its importance by the changes that may occur during the magnetic field inversion at the scale of the Earth.
Domaines
- Mathématiques [math]
- Théorie des groupes [math.GR]
- Sciences du Vivant [q-bio]
- Bio-Informatique, Biologie Systémique [q-bio.QM]
- Sciences de l'ingénieur [physics]
- Acoustique [physics.class-ph]
- Traitement du signal et de l'image [eess.SP]
- Physique mathématique [math-ph]
- Planète et Univers [physics]
- Astrophysique [astro-ph]
- Sciences de la Terre