Core processes responsible for the geomagnetic field dissipate energy by two competing mechanisms that both depend on the electrical conductivity, 
, or equivalently the reciprocal quantity, resistivity, 
. The obvious dissipation is ohmic heating. A current of density i (amperes/m2) flowing in a medium of resistivity 
(ohm m) converts electrical energy to heat at a rate 
(watts/m3). Thus one requirement for a planetary dynamo is a sufficiently low value of 
(high 
) to allow currents to flow freely enough for this dissipation to be maintained. In a body the size of the Earth, this means that the core must be a metallic conductor. However, a metal also has a high thermal conductivity, introducing a competing dissipative process (see Core, thermal conduction ). The stirring of the core that is essential to dynamo action maintains a temperature gradient that is at or very close to the adiabatic value (see also Core, adiabatic gradient) and conduction of heat down this gradient is a drain on...
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Bibliography
Stacey, F.D., 1992. Physics of the Earth, 3rd edn. Brisbane: Brookfield Press.
Stacey, F.D., and Anderson, O.L., 2001. Electrical and thermal conductivities of Fe‐Ni‐Si alloy under core conditions. Physics of Earth and Planet Interiors, 124: 153–162.
Stevenson, D.J., 2003. Planetary magnetic fields. Earth Planetary Science Letters, 208: 1–11.
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Stacey, F.D. (2007). Core, Electrical Conductivity. In: Gubbins, D., Herrero-Bervera, E. (eds) Encyclopedia of Geomagnetism and Paleomagnetism. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-4423-6_45
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