Coupling of magnetospheric and field-aligned currents by satellite-based observations

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Electric current flowing in the near-equatorial magnetosphere(L--4-9 R_E)consists of two basic elements : azimuthal current and radial current. Azimuthal current flows westward around the earth. Radial current flows toward the earth in the late-evening to premidnight sector and away from the earth in the midnight to early-morning sector.Presence of magnetospheric radial current is consistent with the counter current of ionosphere Pedersen current at auroral latitudes that is projected in the magnetospheric equatorial plane.Inhomogenuity in azimuthal and radial current associates field-aligned current(FAC)and forms a three-dimensional current loop, respectively. Region 1 FAC and Region 2 FAC that are determined at low altitudes, manifest the superimposed, resultant effect of these current loops.During the substorm growth phase, ion plasma sheet that was inferred from the precipitating particles, consists of core part and cleft-like part. In the ion core part domain, enhanced westward azimuthal current loop associates Region 2-sense FAC and furthermore radial current loop causes Region 2 plus Region 1-sense FAC in pair. In the domain of ion cleft-like part, Region 1-sense FAC is associated with the convective flow vorticity in the near equatorial magnetotail. Whereas, in the expansion phase, disruption occurs rapidly in the preceding(growth phase), enhanced westward current and the growth phase-ion core part trns into the explosive part. Region 1-sense FAC is associated with this current disruption and reversed-Region I sense FAC(and/or multiple current shetts)is also associated, pole-ward of and adjacent-to the disruption region. The ion core part shifts far equator-ward and associates Region 2-sense FAC, and c upled Region 2 plus Region 1 FAC there.