Geomagnetic field, global pattern

The geomagnetic field is generated in the fluid outer core region of the Earth by electrical currents flowing in the slowly moving molten iron. In addition to sources in the Earth’s core, the geomagnetic field observable on the Earth’s surface has sources in the crust and in the ionosphere and magnetosphere. The signal from the core dominates, accounting for over 95% of the field at the Earth’s surface. The geomagnetic field varies on a range of scales, both temporal and spatial; the description of the variations made here concentrates on the recent spatial and temporal variations of the field with origins in the Earth’s core that can be surmised from observations made over the last four centuries.