Figure 1: Magnetic field components recorded on November 25, 1997 by the WIND (blue), GEOTAIL (green), and IMP8 (red) spacecraft, plotted in GSM coordinates. The WIND data have been shifted by +60 min and scaled by a factor of 4, while the IMP8 data have been shifted by -20 min.
Figure 2: Stackplots of LOS velocities from three SuperDARN radar beams and several range-gates chosen to represent a wide range of MLT. The vertical dotted line indicates the earliest observed change in the ionospheric convection. It is evident from the dramatic changes in all the LOS velocities that the ionospheric response to the change in IMF is nearly instantaneous across the MLT range covered.
Figure 3: 2-min convection maps as measured by the Northern Hemisphere component of SuperDARN from a) 1700 to 1702 UT and b) 1704 to 1706 UT showing a transition of ionospheric convection consistent with a +BZ, -BY to -BZ, +BY IMF change. The cross polar cap potential increased from 35 kV to 49 kV during this period. The coverage of ionospheric echos shown was typical during the hour preceding and following the first significant response to the sudden change in the IMF.
Figure 4: The X-Y plane showing the locations of the spacecraft (WIND, GEOTAIL, and IMP8) which observed the BZ-BY change (shown in Figure 1), a model bow shock after Peredo et al. , a model magnetopause after Roelof and Sibeck , and the intersection with planes containing the IMF at four propagation times from WIND; the time of the WIND observation, the time of the GEOTAIL observation, 2 minutes prior to the enhanced ionospheric convection observation, and the time of the IMP8 observation.