Magnetostrophic MRI in the Earth's outer core
Article first published online: 15 AUG 2008
Copyright 2008 by the American Geophysical Union.
Geophysical Research Letters
Volume 35, Issue 15, August 2008
How to Cite
2008), Magnetostrophic MRI in the Earth's outer core, Geophys. Res. Lett., 35, L15305, doi:10.1029/2008GL034395., , and (
- Issue published online: 15 AUG 2008
- Article first published online: 15 AUG 2008
- Manuscript Accepted: 26 JUN 2008
- Manuscript Revised: 13 JUN 2008
- Manuscript Received: 18 APR 2008
- dynamics of the Earth's core;
- magnetorotational instability;
- secular variation
 We show 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. It requires either 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 very 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 give a simple physical explanation of the instability, and show that it relies on a force balance appropriate to the Earth's core, known as magnetostrophic balance.