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Electrical conductivity of the lowermost mantle explains absorption of core torsional waves at the equator

Nathanaël Schaeffer 1 Dominique Jault 1
1 Géodynamo [2016-2019]
ISTerre - Institut des Sciences de la Terre
Abstract : Torsional Alfvén waves propagating in the Earth's core have been inferred by inversion techniques applied to geomagnetic models. They appear to propagate across the core but vanish at the equator, exchanging angular momentum between core and mantle. Assuming axial symmetry, we find that an electrically conducting layer at the bottom of the mantle can lead to total absorption of torsional waves that reach the equator. We show that the reflection coefficient depends on G Br , where Br is the strength of the radial magnetic field at the equator, and G the conductance of the lower mantle there. With Br = 7e-4 T., torsional waves are completely absorbed when they hit the equator if G = 1.3e8 S. For larger or smaller G, reflection occurs. As G is increased above this critical value, there is less attenuation and more angular momentum exchange. Our finding dissociates efficient core-mantle coupling from strong ohmic dissipation in the mantle.
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https://hal-insu.archives-ouvertes.fr/insu-01302757
Contributor : Nathanaël Schaeffer <>
Submitted on : Thursday, April 14, 2016 - 11:53:36 PM
Last modification on : Wednesday, October 14, 2020 - 4:18:52 AM
Long-term archiving on: : Tuesday, November 15, 2016 - 3:35:37 AM

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  • HAL Id : insu-01302757, version 1
  • ARXIV : 1604.04525

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Nathanaël Schaeffer, Dominique Jault. Electrical conductivity of the lowermost mantle explains absorption of core torsional waves at the equator. 2016. ⟨insu-01302757⟩

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