Skip to Main content Skip to Navigation
Journal articles

Approaching a realistic force balance in geodynamo simulations

Abstract : Earth sustains its magnetic field by a dynamo process driven by convection in the liquid outer core. Geodynamo simulations have been successful in reproducing many observed properties of the geomagnetic field. However, although theoretical considerations suggest that flow in the core is governed by a balance between Lorentz force, rotational force, and buoyancy (called MAC balance for Magnetic, Archimedean, Coriolis) with only minute roles for viscous and inertial forces, dynamo simulations must use viscosity values that are many orders of magnitude larger than in the core, due to computational constraints. In typical geodynamo models, viscous and inertial forces are not much smaller than the Coriolis force, and the Lorentz force plays a subdominant role; this has led to conclusions that these simulations are viscously controlled and do not represent the physics of the geodynamo. Here we show, by a direct analysis of the relevant forces, that a MAC balance can be achieved when the viscosity is reduced to values close to the current practical limit. Lorentz force, buoyancy, and the uncompensated (by pressure) part of the Coriolis force are of very similar strength, whereas viscous and inertial forces are smaller by a factor of at least 20 in the bulk of the fluid volume. Compared with nonmagnetic con-vection at otherwise identical parameters, the dynamo flow is of larger scale and is less invariant parallel to the rotation axis (less geostrophic), and convection transports twice as much heat, all of which is expected when the Lorentz force strongly influences the convection properties.
Document type :
Journal articles
Complete list of metadatas

Cited literature [41 references]  Display  Hide  Download
Contributor : Eva Fareau <>
Submitted on : Thursday, August 16, 2018 - 4:36:41 PM
Last modification on : Friday, March 27, 2020 - 2:09:59 AM
Long-term archiving on: : Saturday, November 17, 2018 - 1:07:45 PM


Publisher files allowed on an open archive




Rakesh Yadav, Thomas Gastine, Ulrich Christensen, Scott Wolk, Katja Poppenhaeger. Approaching a realistic force balance in geodynamo simulations. Proceedings of the National Academy of Sciences of the United States of America , National Academy of Sciences, 2016, 113 (43), pp.12065-12070. ⟨10.1073/pnas.1608998113⟩. ⟨insu-01857575⟩



Record views


Files downloads