Hori, K.

Jones, C.A.

Teed, R.J.

Tobias, S.M.

English

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Excitation mechanism of waves in the Earth's core

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TalksExcitation mechanism of waves in the Earth’s coreC. A. Jones*, R. J. Teed, K. Hori and S. M. TobiasUniversity of LeedsAxisymmetric torsional waves have been observed in the Earth’s core, and ithas been suggested that the waves may originate near the tangent cylinder, theaxial cylinder in the Earth’s liquid core which touches the solid inner core. Thereis a theoretical expectation that the fluid inside the tangent cylinder will be morethermally and compositionally buoyant than the fluid outside the tangent cylinder.At the tangent cylinder, there will be strong thermal and compositional gradients,exciting convection in the form of travelling magnetic Rossby waves. These magneticRossby waves can have periods close to that of the torsional Alfven waves in thecore, and hence they can trigger trains of torsional waves travelling outwards fromthe tangent cylinder region.We have investigated this resonant excitation mechanism using a magnetocon-vection based approach, which has been adapted from a spherical shell convectiondriven dynamo code. This enables us to get to a regime of strong fields and lowEkman numbers, at the cost of specifying the form of the magnetic field rather thanallowing it to arise naturally from the dynamo model. Low Ekman number is essen-tial to see the wave excitation, as the tangent cylinder convecting layer is expectedto be only a few hundred kilometres thick, and viscosity must be small enough toallow convection on these scales. We are currently exploring the conditions underwhich the resonance between the convection and the torsional oscillations can occur.We have also investigated non-axisymmetric magnetic Rossby waves in the outercore, as these wave also have frequencies which might be detectable by magneticsatellite observations in the near future.5

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Excitation mechanism of waves in the Earth's core

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