A model of the distributed magnetospheric currents

Abstract

A model of the quiet time ring current and the tail currents has been developed for quiet magnetic conditions and perpendicular incidence of the solar wind on the main (dipolar) field of the earth. Previous work of several authors has shown that these distributed currents flow throughout the magnetosphere and that they are produced by the drift of charged particles in the nonuniform magnetic field B and by plasma diamagnetism. The currents are modeled from a few thousand kilometers above the earth's surface to distances of over 200 RE back in the tail of the magnetosphere. This procedure allows the computation of the magnetic field BD, associated with these distributed currents to beyond lunar orbit. The currents are chosen so that BD correctly models observed field features in the inner magnetosphere and the magnetotail. Although the tail currents can be formed continuously by the entry of magnetosheath particles into the equatorial flanks of the tail even during quiet times, the ring currents must be supplied at irregular (substorm or storm) intervals when dynamic processes are operative. These currents make significant contributions to the earth's surface field variations (e.g., in Sq and Dst). The formation of the tail currents implies that the magnetosphere is open (in the equatorial regions of the tail) to low-energy charged particles. This model work also suggests that when magnetospheric particles and fields are considered self-consistently, it is not possible to produce a magnetically closed magnetosphere. The static magnetic field associated with this distributed current model exhibits a neutral line beyond the orbit of the moon. The inclusion of the field associated with these distributed currents in a model of the total magnetic field should yield better agreement between observed magnetospheric particle and field phenomena and model calculations.