Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000geoji.140..453l&link_type=abstract
Geophysical Journal International, Volume 140, Issue 2, pp. 453-459.
Astronomy and Astrophysics
Astronomy
5
Earth'S Magnetic Field, Geomagnetic Field, Induced Magnetization
Scientific paper
We analyse the external magnetic field generated by a spheroidal shell of constant susceptibility when it is magnetized by an internal magnetic field of arbitrary complexity. The analysis is relevant to the generation of the Earth's crustal magnetic field by the internal core field. We find an analytical expression for such a crustal field that is expressed in an oblate spheroidal coordinate system, valid for arbitrary flattening, shell thickness and susceptibility. Our exact calculation takes into account magnetization due to the magnetic field of the crust itself, generating an external field that depends on terms both linear and non-linear in the susceptibility. Each spheroidal harmonic coefficient of the external field is generated by and proportional to the same coefficient in the expansion of the inducing field. The terms linear in the susceptibility are generated by the flattening of the Earth, and would otherwise vanish (by Runcorn's theorem) in the spherical case. For a geophysically relevant model, the crustal field is weak, generated primarily by the non-linear terms, and dominated by long wavelengths.
Jackson Andrew
Lesur Vincent
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