Axial invariance of rapidly varying diffusionless motions in the Earth's core interior

Dominique Jault (1)

1 LGIT - Laboratoire de Géophysique Interne et Tectonophysique

Geostrophic jets propagating as Alfvén waves are shown to arise ina rapidly rotating spherical shell permeated by a magnetic field among the transient motions set up by an impulsive rotation of the inner core. These axially invariant motions evolve on a time-scale which is short compared to the magnetic diffusion time. The numerical study is taken as illustrative of a more general point: on such a fast time-scale the dimensionless number appropriate to compare the rotation and magnetic forces is independent of the magnetic diffusivity in contrast with the often used Elsasser number. Extension of the analysis to non-axisymmetrical motions is supported by published studies of dynamo models and magnetic instabilities.

Mots clés: Earth's core; Magneto-hydrodynamic waves; Geomagnetic field; Core flow

Domaines: Géophysique [physics.geo-ph]

Dominique Jault. Axial invariance of rapidly varying diffusionless motions in the Earth's core interior. Physics of the Earth and Planetary Interiors, 2008, 166, pp.67-76. ⟨10.1016/j.pepi.2007.11.001⟩. ⟨hal-00323192⟩