Fig. 5

One-minute ASI sequences of 3-s cadence all-sky images at ground stations, highlighting auroral structuring and intensifications. Within each panel, the time sequence is to the right and down (like reading text). Within each image, north is at the top and east to the right. In all images, a bright spot to the leftor lower leftis the Moon. The top left panelsshow RANK/GILL images whose central pixels form part of the keogram of Fig. 4. A growth phase arc is visible below the Moon in the RANK images, while the upper partof the GILL images is traversed by a brightening arc which first became visible in the previous minute. The right columnshows RANK/GILL and KUUJ at the times indicated at the right of each image. A new arc which became visible at 04:26:21 at KUUJ is highlighted at 04:26:27 by a red arrow. This new arc formed structure and moved toward the east in the field of view. At the lower left, a single panel shows brightening and structuring of the polemost arc at RANK in the minute of 04:38 UT