magnetostrophic MRI in the Earth's outer core : linear and non-linear developements.

Details magnetostrophic MRI in the Earth's outer core : linear and non-linear developements. magnetostrophic MRI in the Earth's outer core : linear and non-linear developements.

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmgp11a0699l&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #GP11A-0699

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1510 Dynamo: Theories And Simulations, 1522 Paleomagnetic Secular Variation, 1530 Rapid Time Variations, 1560 Time Variations: Secular And Longer

Scientific paper

We have shown that a simple, modified version of the Magnetorotational Instability (MRI) can develop in the outer liquid core of the Earth, in the presence of a background shear (Petitdemange, Dormy, Balbus, GRL,35, 2008). It requires either a thermal wind, or a primary instability, such as convection, to drive a weak differential rotation within the core. The force balance in the Earth's core is unlike classical astrophysical applications of the MRI (such as gaseous disks around stars). Here, the weak differential rotation in the Earth core yields an instability by its constructive interaction with the planet's much larger rotation rate. The resulting destabilising mechanism is just strong enough to counteract stabilizing resistive effects, and produce growth on geophysically interesting timescales. We refer to this instability as the magnetostrophic MRI (MS-MRI). We investigate linear and nonlinear developments of the MS-MRI. We present global numerical simulations both axisymmetric and weakly-three- dimensional (i.e. involving a limited number of azimuthal modes). We discuss the possible signature of MS- MRI in geomagnetic observations and address the connection between the MS-MRI and the Geodynamo.

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