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Article

Magnetic Helicity and the Geodynamo

Department of Physics and Astronomy, George Mason University, Fairfax, VR 22030, USA
Academic Editors: Ioannis Sarris and Gang Li
Fluids 2021, 6(3), 99; https://doi.org/10.3390/fluids6030099
Received: 13 January 2021 / Revised: 10 February 2021 / Accepted: 19 February 2021 / Published: 2 March 2021
(This article belongs to the Special Issue Fluids in Magnetic/Electric Fields)
We present theoretical and computational results in magnetohydrodynamic turbulence that we feel are essential to understanding the geodynamo. These results are based on a mathematical model that focuses on magnetohydrodynamic (MHD) turbulence, but ignores compressibility and thermal effects, as well as imposing model-dependent boundary conditions. A principal finding is that when a turbulent magnetofluid is in quasi-equilibrium, the magnetic energy in the internal dipole component is equal to the magnetic helicity multiplied by the dipole wavenumber. In the case of the Earth, measurement of the exterior magnetic field gives us, through boundary conditions, the internal poloidal magnetic field. The connection between magnetic helicity and dipole field in the liquid core then gives us the toroidal part of the internal dipole field and a model value of 3 mT for the average core dipole magnetic field. Here, we present the theoretical analysis and numerical simulations that lead to these conclusions. We also test an earlier assertion that differential oblateness may be related to dipole alignment, and while there is an effect, rotation appears to be far more important. In addition, the relationship between dipole quasi-stationarity, broken ergodicity and broken symmetry is clarified. Lastly, we discuss how inertial waves in a rotating magnetofluid can affect dipole alignment. View Full-Text
Keywords: dynamo; magnetohydrodynamics; statistical mechanics; turbulence dynamo; magnetohydrodynamics; statistical mechanics; turbulence
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MDPI and ACS Style

Shebalin, J.V. Magnetic Helicity and the Geodynamo. Fluids 2021, 6, 99. https://doi.org/10.3390/fluids6030099

AMA Style

Shebalin JV. Magnetic Helicity and the Geodynamo. Fluids. 2021; 6(3):99. https://doi.org/10.3390/fluids6030099

Chicago/Turabian Style

Shebalin, John V. 2021. "Magnetic Helicity and the Geodynamo" Fluids 6, no. 3: 99. https://doi.org/10.3390/fluids6030099

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