The Earth's Magnetic Field

Abstract The Earth's magnetic field is generated in the fluid region deep inside the Earth. Heat convection, buoyancy forces, and planetary rotation cause the iron‐rich fluid in the outer core to flow in a complex way and the movement of this electrical conductor through existing magnetic field generates electrical current. This produces more magnetic field in an advective process. Some of it diffuses away resulting in a reasonably stable magnetic field, which is broadly dipolar outside the planet and which occasionally reverses its polarity. Parameters of the Earth's magnetic field observed near the surface of the planet vary in space and time over wide ranges. As well as processes acting in the deep interior of Earth, the crust, the ionosphere, the magnetosphere, and the Sun all contribute to the observed magnetic field. Indeed, the magnetosphere is formed by the interaction of the solar wind, moving radially outwards from the Sun at supersonic speeds, with the Earth's magnetic field (see also The Plasma and Radiation Environment in Earth Orbit). Geomagnetic observations are made at fixed sites at observatories, and extensive surveys are carried out on land, at sea, and from aircraft and satellites; the magnetic properties of rocks provide further information. The Earth's magnetic field is important for many aerospace applications today, and these areas are especially considered.