Figure 7: Temporal brightening of S II 1256Å emission compared to various neutral emission lines: (A) neutral UV emission lines from STIS data over a 2´´ × 4´´ aperture; (B) the [O I] 6300Å line from groundbased data over a 5´´ × 5´´ aperture; and (C) the S II 1256Å line from STIS data over a 1.4´´ × 4´´ aperture (disk) and a 1.4´´ × 10´´ aperture excluding the central 1.4´´ × 4´´ (triangle). All apertures are centered on Io. 1 R_Io= 0.55´´ The aperture width in (C) is reduced to exclude light from nearby emission lines.