Geomagnetism is the geophysical method for the measurement and analysis of the geomagnetic field. The geomagnetic field is generated by electric currents located in many different parts of the Earth. In the outer core the main part of the geomagnetic field is sustained by a naturally occurring dynamo. In the mantle currents can be induced by time-dependent variations in the ambient magnetic field. In the crust the field has both induced and permanent components. And, in the ionosphere and magnetosphere electric currents are sustained through a complicated interaction with the Sun, the heliomagnetic field, and the solar wind of charged particles. The many different, and sometimes remote, sources of the Earth's magnetic field each contribute to the total field at any one particular location, with the very different physical processes in each domain giving rise to a wide variety of time-dependent geomagnetic variations.
Some aspects of the use of Geomagnetism to study the structure of the upper mantle of the Earth are considered below.
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