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Title: The analysis of geomagnetic storm-time variations
Author: Davidson, Nigel Charles
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1992
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The earth is bathed in an ever changing magnetic environment due to fluctuations in the solar wind. The external field induces currents within the earth which cause a secondary internal field. The ratio of internal to external parts of the magnetic potential is known as the response and may be derived from measurements of the field at the surface. The response of the earth is dependent on the spatial form of the field and distribution of conductivity within the earth. The analysis of numerous geomagnetic storms, large disturbances in the field surrounding the whole earth, is presented with the aim of determining a reliable response function which enables an estimate to be made of the average conductivity of the upper mantle. The compilation of a database of geomagnetic storms was a major part of the work. All the suitable storm events were selected between 1957 and 1982 to give 44 storms. The entire set of hourly values were checked for errors and corrections made where necessary. Where data were missing their values were interpolated using information from nearby observatories. The lower the frequency of external magnetic variations the deeper the penetration into the earth. The frequency content of geomagnetic storms allows depths approaching 1500km to be investigated. The observations of magnetic field were Fourier transformed and attention focussed on the Fourier coefficients of the lowest frequencies, 0.03 to 1 cycle per day. From Spherical Harmonic Analysis in the frequency domain it was found that a pure P1o spherical harmonic model is acceptable for the spatial form of the field at the frequencies of most interest. Thus the source is assumed to be a simple ring current in common with most of the previous research. The Fourier coefficients of the X and Z magnetic components were then fitted to the appropriate P1o model which allows the separate internal and external parts to be evaluated. A robust method, to reduce the influence of anomalous values, was used for determining the optimum fit to the Fourier coefficients. The technique was assessed by examining the distribution of residuals.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available