Substorm current in the equatorial plane of the magnetosphere deduced from ground‐based magnetometer chain records

The purpose of this paper is to demonstrate the feasibility of inferring the distribution of substorm electric currents in the equatorial plane on the basis of ionospheric current vectors and field-aligned currents during substorms; the ionospheric current vectors are obtained from the ground-based magnetometer network by using the KRM inversion algorithm [Kamide et al,. 1996] and the longitudinal and latitudinal current loops proposed by Bostrom [1964]. A simple model of the magnetosphere is used to trace field lines for our demonstration purposes. It is found that the calculated radial currents in the equatorial plane are in good agreement with the statistical results obtained by Iijima et al. [1990] on the basis of the satellite AMPTE/CCE data. We show also that the statistical azimuthal currents are mainly composed of the ring current and the cross-tail current. The ionospheric contribution to the azimuthal component is estimated to be about 20% of the total current. Therefore both results deduced from the ground-based magnetometer network and from AMPTE/CCE satellite data are useful in studding the distribution of substorm currents in the equatorial plane, in spite of the fact that they are based on entirely different methods and that a simple magnetosphere model is used to trace field lines.