Introduction

In this chapter we will look at some of the ways in which geomagnetism finds utility in today's world. The main subjects are the impact of the geomagnetic field on modern technological systems and the application of geomagnetism to the discovery of the physical nature of our world. I also include interesting observations for which geomagnetic connections imply future application directions.

Each period range of natural geomagnetic field fluctuations can be identified with special utilization topics. For example, consider the following:

1. (a) For the period range from 0.25 seconds to 1 minute the primary subjects of interest are Earth crust exploration, detection of hidden conductivity anomalies, electric power transformer failures, studies of hydromagnetic wave propagation, and discovery of magnetospheric processes.

2. (b) For the range from 1 minute to 24 hours, studies include the structure of magnetospheric deformation and currents, thermospheric heating and winds, ionospheric currents and tides, and conductivity characteristics of the Earth's lower crust, mantle, and continental coastlines. Geomagnetic storms in this time scale affect a multitude of man-made systems such as satellites, communication systems, electric-power grids, and long pipelines (see Heirtzler et al., 2002).

3. (c) From the range 1 day to 1 year we obtain information about the fluid motions within the Earth's core and at the core–mantle boundary, solar activity and solar sector changes, tropospheric weather changes, and magnetospheric deformation. Our main field magnetic navigation charts are obtained from data in this period range.