Introduction
Magnetohydrodynamics (MHD) is the study of the flow of electrically conducting fluids in the presence of magnetic fields. It has significant applications in technology and in the study of planets, stars, and galaxies. Here the main focus will be on its role in explaining the origin and properties of the geomagnetic field.
The interaction between fluid flow and magnetic field defines the subject of MHD and explains much of its fascination (and complexity). The magnetic field B influences the fluid motion V through the Lorentz force, 
. The electric current density J is affected by the fluid motion through the electromotive force (emf), 
. The most famous offspring of this marriage of hydrodynamics to electromagnetism are the Alfvén waves, a phenomenon absent from the two subjects separately (see Alfvén waves ). In fact, many consider the discovery of this wave by Hannes Alfvén in 1942 to mark the birth of MHD (see Alfvén, Hannes ). Initially MHD was often known as...
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Roberts, P.H. (2007). Magnetohydrodynamics. In: Gubbins, D., Herrero-Bervera, E. (eds) Encyclopedia of Geomagnetism and Paleomagnetism. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-4423-6_203
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