Magnetospheric currents

After outlining the constituent parts of the magnetospheric system, a historical review is presented of studies of the earth's magnetic field. It is noted that a connection between the aurora and variations in the magnetic field was first suggested by Halley in 1716. In discussing the magnetosphere, it is pointed out that the geomagnetic field can be thought of as being produced by a huge bar magnet embedded in the earth, with the axis of the magnet tilted away slightly from the earth's rotational axis. Attention is also given to the interplanetary magnetic field, to the relationship between the interplanetary magnetic field and the geomagnetic field, to convective flow, to field-aligned currents, and to Birkeland currents and auroral emissions. Various questions concerning the Birkeland currents are summarized.