Physics
Scientific paper
Oct 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976geoj...47...19g&link_type=abstract
Geophysical Journal, vol. 47, no. 1, Oct. 1976, p. 19-39.
Physics
13
Dynamo Theory, Earth Core, Geomagnetism, Conducting Fluids, Convective Flow, Earth Mantle, Electrical Resistivity, Heat Flux, Liquid Flow, Magnetic Field Configurations, Resistance Heating, Thermal Conductivity
Scientific paper
The paper attempts to determine how the various parameters needed to model a dynamo process in earth's liquid core are constrained by observations made at the surface. It is assumed that any model must match the observed magnetic field, that the convective processes must not transmit more heat through the core-mantle boundary than is seen to emerge from the surface, and that the Wiedemann-Franz law relating electrical and thermal conductivities holds. Some current ideas on the state of the core are reviewed, two different heat sources are considered, and the thermal flux is estimated. The estimate of the ohmic heat flux is improved by including the effect of the toroidal magnetic field, and the convected heat flux is analyzed. It is shown that: (1) between 20 and 50 GW of heat must emerge from the core, (2) a large toroidal field probably cannot be generated by thermal convection, (3) the outer regions of the liquid core are likely to be stably stratified or convecting at too slow a rate to help with magnetic-field generation, and (4) the dynamo can be driven with a much smaller total heat flux if the heat source is at depth, such as freezing of the inner core.
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