geomagnetism: external fields Not only does the Earth have its self-generated internal magnetic field (see magnetic field, origin of the internal field ); it is also surrounded by magnetic fields formed outside the Earth. These fields are called external fields. External fields originate as a result of complex conditions created in Earth's vicinity by the interactions of solar wind, solar radiation, the Earth's internal field, and the Earth's atmosphere. Extremely high temperatures prevail in the Sun's corona, a region immediately above the surface of the Sun. In the corona, protons and electrons of solar hydrogen can exist separately as charged particles in an ionized state known as ...