The May 7, 1996 event occurred in the southern hemisphere while Polar swept through perigee. Plate 9 presents an auroral image from VIS. During the event, the field of view of VIS Earth camera covered a portion of the polar cap in which a section of the arc was observed from 01:04:47 to 01:11:32 UT. Although the intensity of the arc is extremely low, it is relatively higher than the emissions in the polar cap so that clear theta-aurora-like images may be discerned. Based on the auroral geometry shown in Plate 9, the observed emissions most likely came from a transpolar arc. Plate 10 shows Hydra electron and ion measurements for this event. A region of plasma sheet-like plasmas was observed from 01:08:40 to 01:11:05 UT. Strong polar rain fluxes were detected outside this region, indicative of southward IMF during this period. From Hydra results and the Polar footprint, marked by a while circle outside the right image in Plate 9, the auroral arc is farther extended to the magnetic pole. Figure 11 shows the IMF measurements from 20:00 UT May 6 to 04:00 UT May 7, 1996 with a time delay of ~ 12 mins for the propagation of the solar wind. After two hours of northward IMF Bz, the IMF turned southward at 23:15 CUT, as shown in the bottom panel. The Bz component then oscillated for 24 mins and became continuously negative, but small, for more than two hours. The IMF By component was very steady, negative before 00:18 CUT and positive afterward, except briefly negative at 00:42 CUT, as shown in the third panel.
Please send questions, comments, or suggestions about the paper to:
Shen-Wu Chang
Department of Physics and Astronomy, The University of Iowa, Iowa City, IA 52242
Phone:(319)335-3828; Fax:(319)335-1753;
swc@space-theory.physics.uiowa.edu