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.