The November 1, 1996 event occurred in the northern hemisphere. Figure 10 shows the IMF measurements from 18:00 UT October 31 to 08:00 UT November 1, 1996 with a delay time of ~ 27 mins for the propagation of the solar wind. As shown in the bottom panel, the IMF was persistently northward for more than 10 hours starting at 21:11 CUT October 1, 1996, except for a few, brief southward turnings of less than 5 mins duration. During the first four hours of the northward IMF interval, Bz was very small, < 2 nT, and then it increased to ~ 5 nT. Auroral images from VIS are available only after 00:46 UT when the theta aurora had become well developed. The observed auroral pattern lasts about one and a half hour indicated by a bar in the bottom panel but the luminosity of the transpolar arc dimmed gradually. Plate 7 presents two examples of theta auroral images. These images were taken while Polar was traversing magnetic field lines associated with the transpolar arc. Plasma measurements from Hydra are shown in Plate 8. Intermittent, plasma sheet-like electron and ion fluxes were surrounded by weak polar rain. Polar trajectory was basically along the noon-midnight meridian, from midnight to noon. The energy and energy flux are lower in the early plasma bursts (~ 00:45 and 01:30 UT) than the later ones (~ 04:00 and 05:00 UT) which may actually be parts of dayside auroral oval fluxes that were detected by Hydra when Polar had moved very close to the oval. Before 00:46 CUT, IMF Bz was negative during periods beginning at 23:55, 23:16, and 22:17 CUT, respectively; these are all possible candidates to trigger the theta aurora based on the model of Newell and Meng [1995]. It is also noticed that there is a significant change in the By component at 22:25 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