Open AccessElectromagnetic Induction in the Mantle by Aperiodic Variations
Author(s) -
Jady R. J.
Publication year - 1975
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1975.tb01607.x
Subject(s) - aperiodic graph , geology , mantle (geology) , geophysics , electromagnetic induction , seismology , physics , mathematics , combinatorics , quantum mechanics , electromagnetic coil
Summary The theory of electromagnetic induction in a uniformly conducting sphere by aperiodic variations was first studied by Price, and extended to the case when the conductivity varies as any power of the radial distance by Lahiri & Price. In this paper the governing electromagnetic diffusion equation is solved numerically using a Crank‐Nicolson type formula. Various profiles that have been proposed for the mantle are tested using the analyses of Dst by Chapman & Price, Rikitake & Sato, Anderssen & Seneta, and the provisional results for the latest analysis by Anderssen, Doyle, Petersons & Seneta. It is found that the Dst analyses are not accurate enough to allow a conductivity structure to be determined with precision. They are, however, useful in providing additional checks on models that have been determined by other long‐period variations. In this paper it is found that they are compatible with a conductivity profile determined by the harmonics of Sq and the 27‐day variation. The main features of this profile are a rise in conductivity, between 500 and 600 km, to about 1 mho m‐ ‐1 , and a levelling off at this value to at least 1200 km, or so, from the surface.