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Title: Electromagnetic induction in the earth and oceans
Author: McKirdy, David McAllister
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1980
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The introduction contains a review of published work on the oceanic induction problem up to the end of November 1979 and concentrates on induction in the ocean by magneto variations, although a brief account is also given of dynamo processes. The aim of the research was to model the effects of mutual induction between oceanic electric currents and a finitely conducting mantle, since previous authors had only considered the simpler case of a perfectly conducting mantle. A method for calculating these effects is derived in Chapter 2 by considering induction by a vertical magnetic dipole at the earth's surface leading to a generalised form of the Hobbs-Price mutual induction kernel. A simple uniform earth and a more realistic seven-layered model represent the mantle while considering induction in a hemispherical ocean, in Chapters 3 and 4 respectively, where details of the calculation of the electromagnetic responses are given. Alterations and improvements were made to an existing computer program so that Bunks' profile could be used to model induction in a thin sheet in the shape of the oceans and contour plots of results obtained with Banks' model and with the perfect conductor are compared in Chapter 5. Using a spherical harmonic representation of the Sq inducing field, a qualitative comparison is made between the equivalent current systems of the modelled results with those computed from observatory measurements at different instants of Universal Time. The use of Banks' profile did not give a better comparison with the observations than the perfectly conducting mantle. The application of spherical harmonic analysis to the complete solutions showed that the electromagnetic responses to each of the principal Sq harmonica were greater with the finitely conducting mantle than with the perfect conductor, while both were greater than the observed responses. When the analysis was restricted to using only the values at the sites of geomagnetic observatories the coefficients of the vertical magnetic field were found to be different from before, while the ratios of internal to external parts were found to be smaller. These discrepancies are due to aliaising by harmonics absent from the analysis and they suggest that the determination of the responses based on spherical harmonic analysis of observatory measurements must be suspect, which will influence any global geoelectric profile determined from these ratios.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available