Ground-based observations at Syowa Station of Event #2 for a 2.5-hour period from 2230 UT on May 25, 2017. Top panels (a)–(e) are shown in the same format as Figure 3. The vertical line at 2325 UT indicates the beginning of the expansion phase of the substorm. The bottom panels show the all-sky maps of (f) CNA and (g) aurora from the ground view at 2307 UT, as indicated by the blue dotted line. The white diamonds represent the beam directions of the PANSY radar.