The magnetic field of a bar magnet has a simple configuration known as a dipole field. Close to Earth's surface this field is a reasonable approximation of the actual field.
geomagnetic field, Magnetic field associated with the Earth. It is essentially dipolar (i.e., it has two poles, the northern and southern magnetic poles) on the Earth’s surface. Away from the surface, the field becomes distorted. Most geomagnetists explain the field by means of dynamo theories, whereby a source of energy in the Earth’s core causes a self-sustaining magnetic field. In the dynamo theories, fluid motion in the Earth’s core involves the movement of conducting material within an existing magnetic field, thus creating a current and a self-enforcing field.
