Fine examples of both conjugate and nonconjugate isolated auroral arcs were observed at two geomagnetically conjugate stations near L=6, Syowa Station in Antarctica and Husafell in Iceland on September 12, 1988. These events exhibited some interesting characteristics. An auroral loop structure that appeared in both hemispheres was ~2.0 times larger in the north-south direction at Syowa than at Husafell. This scale difference is greater than expected from the difference in geographic and geomagnetic (IGRF) coordinates between the two points of observation. However, temporal and spatial variations in the loop structures were almost identical in both hemispheres. After the disappearance of the loop structure, closely conjugate auroras were formed. Nonconjugate auroral features appeared again at Syowa on the poleward side, while the equatorward auroras maintained conjugacy. The nonconjugate aurora at Syowa then began to break up, showing fast moving vortex-like structures (auroral spirals). At this time, all auroral features at Husafell seemed to have their conjugate counterparts in equatorward auroras at Syowa and none exhibited rapid motions. These conjugate auroras at Husafell were gradually extending poleward, while the corresponding features at Syowa were compressed toward the equator and shrinking in size. The onset of auroral breakup was about one minute earlier at Syowa than at Husafell. The nonconjugate auroral features were reflected in corresponding magnetic field variations on the ground. The events summarized above give interesting clues to the development and decay of auroral conjugacy and the question why the beginning of auroral breakup is not simultaneous at conjugate stations. The time lag and nonconjugacy of auroral breakup in conjugate areas suggests that the triggering source of auroral breakup was not located near the equatorial plane in the magnetosphere but most likely in a localized region near the ionosphere in the southern hemisphere. The nonconjugate auroral spirals also suggest the existence of asymmetrical field-aligned currents. ¿ 1998 American Geophysical Union