MAPPING OF THE IONOSPHERIC FIELD-ALIGNED CURRENTS TO THE EQUATORIAL MAGNETOSPHERE

The assimilative mapping of ionospheric electrodynamics (AMIE)-derived ionospheric field-aligned current patterns during the ninth Coordinat ed Data Analysis Workshop substorm event have been mapped to the magne tospheric equatorial plane, using the data-based magnetospheric magnet ic field model [Tsyganenko, 1995]. We find that at the onset of the su bstorm expansion phase, a pair of field-aligned currents emerges about 8 R-E tailward of the Earth, near the x axis. This pair of field-alig ned currents is consistent with the substorm current wedge model; it l ines up in the east-west direction across the near-Earth tail current and has the sense of the nightside region 1 current, i.e., flowing int o the ionosphere on the east side and out of the, ionosphere on the we st side. The ionospheric counterpart of the substorm wedge currents in the midnight sector, on the other hand, has a northeast-to-southwest alignment. During the expansion phase, the substorm wedge currents int ensify and expand in spatial size; however, their peaks remain nearly at the same location in the equatorial magnetosphere, about 8 R-E tail ward from the Earth. We also find that the intensification of the subs torm wedge currents during the expansion phase is accompanied by the i ntensification of the region 2-sense currents located closer to the Ea rth, and the boundary between the region 2 and substorm wedge currents lies around x = -6 R-E.