Global and regional geomagnetic reference fields

Abstract

The magnetic field at the surface of the earth, when averaged over a sufficient interval of time to remove transient variations (nominally 1 year), consists principally of a contribution originating from the earth's core, called the "main field", with lesser contributions arising from the permanent and induced magnetization of crustal rocks. The International Geomagnetic Reference Field (IGRF) is the internationally adopted set of spherical harmonic models that is intended to represent the main (core) field and its secular variation. Regional models of the geomagnetic field represent a combination of the main field and the broad-scale components of the crustal field. They are used as aids for navigation, surveying, geophysical exploration and studies of large-scale crustal structures, as well as for certain military applications, determination of sea-floor ages, and investigations into geomagnetic phenomena. Analogous with the IGRF, a properly structured set of regional reference field models for Australia, the Australian Geomagnetic Reference Field (AGRF), is being developed. The first step is AGRF1985, the prospective model for the interval 1985 to 1990, that is based on a rectangular harmonic analysis technique.