Figure 3: Shifts in ansa position. The outer vertical dotted lines mark the limits of Io's orbit (5.91 R_J). These images have not had scattered light removed. Although these three images were all aquired at the same System III longitude, the west ansa is at a different position in the middle image than the others, while the east ansa remains unchanged. (This is the opposite of behavior noted earlier [Schneider and Trauger 1995], underscoring the need for synoptic torus observations.) This may reflect a temporally varying and spatially nonuniform east-west (convective) electric field; the brightening of the west ansa is consistent with this hypothesis. The displacement of the ansae here imply values of (the ratio of convection to corotational field strength) given in table III. (Typical values are 0.020-0.030.)