Model geomagnetic disturbance from asymmetric ring current particles

The disturbance field at the earth's surface is calculated for a partial ring current flowing in the earth's dipole field and closing through the ionosphere along field-aligned current paths. The calculation takes into account drift currents, magnetization currents, field-aligned currents, ionospheric currents, and currents induced in the earth. Two types of ionospheric closure are considered, electro jet and distributed, uniform conductivity being assumed. The ring current particles can have arbitrary distributions in energy, in azimuth, and in radial distance from earth. Also, pitch angle anisotropy is allowed. The contribution to the disturbance from these separate factors is given as a function of latitude and longitudinal width of the ring current. We find that most of the disturbance comes from the near-earth part of the field-aligned portion of the current loop. This result implies that the calculated disturbance is relatively insensitive to uncertainties in ionospheric closure and magnetic field distortion in the magnetosphere.