The analysis of geomagnetic storm-time variations

Abstract

One of the geomagnetic variation fields that has particular relevance to the problem of determining the global distribution of electrical conductivity in the upper mantle is the magnetic storm-time variation field, Dst. A mathematical description of such a naturally occurring phenomenon is therefore of importance. Major early contributions to the theory and analysis of magnetic storms were made by Chapman (1918), and later Chapman & Price (1930). With the advantage of modern computing facilities and techniques, and the availability of digitized data from an improved distribution of magnetic observatories, which resulted from the International Geophysical Year 1958, it is now possible to analyse such events for a greatly extended period, up to 10 days or so, after the storm onset. A set of 6 storms are analysed here, two of them occurred during the quiet part of the solar cycle (June 1964, and April 1965), and the remainder during a more active part (February 1969 (2 storms), March 1970, and August 1970). Data at hourly intervals, from at least 58 observatories within + 56° latitude of the geomagnetic equator, were used for each storm. Values of the external and internal parts of the variation field have been obtained, and are given together with their associated errors for the dominant harmonic. An assessment the results, based on statistical arguments, is also given