A ring current is an electric current carried by charged particles trapped in a planet's magnetosphere. It is caused by the longitudinal drift of energetic (10-200 keV) particles.

Earth's Ring Current

Earth's ring current is responsible for geomagnetic storms. The ring current system consists of a band, at a distance of 3-5 R_E(1), which lies in the equatorial plane and circulates clockwise around the Earth (when viewed from the north). The particles of this region produce a magnetic field in opposition to the Earth's magnetic field and so an Earthly observer would observe a decrease in the magnetic field in this area.

Around, the ring current energy is mainly carried by the ions, most of which are protons. However, one also sees alpha particles in the ring current, a type of ion that is plentiful in the solar wind. In addition, a certain percentage are O+ oxygen ions, similar to those in the ionosphere of Earth, though much more energetic. This mixture of ions suggests that ring current particles probably come from more than one source. Ring current particle energies range from 0.05 MeV to 1 MeV.

The Ring Current and Geomagnetic Storms

During a geomagnetic storm, the number of particles in the ring current will increase. At the same time there is a decrease in the geomagnetic field.

See also: Van Allen radiation belt

References:

• 1 -- Introduction to Geomagnetically Trapped Radiation by Martin Walt 1994