The Ring Current, Geomagnetic Disturbance, and the Van Allen Radiation Belts

The large decrease in the horizontal component of the earth's field during the main phase of magnetic storms has been ascribed to the formation or enhancement of a geomagnetic ring current. In this paper we discuss the motions of particles trapped in the earth's dipole field and the resulting ring current. These calculations deal only with a steady state, though during storms the state is changing. The general equations for the current intensity, to obtain the total current and the magnetic field at the earth's center, are applied to the outer radiation belt (V•.) and to a special 'model' belt Va. This Va belt has a particular type of pitch-angle distribution and a number-intensity distribution of Gaussian type along an equatorial radius. The results are considered in connection with magnetic records for several storms and with satellite data. We infer that, during magnetic disturbance, protons of energy of the order of a few hundred kev are intermittently captured between 5 and 8 earth radii and that they produce a transient belt Va. The variety of development of the ring current from one storm to another may be connected with irregularities in the distribution of particles in the solar stream, which may contain tangled magnetic fields.