The event starts at 09:15:23 085 570 UT (t=0 ms). The frame rate of the camera is 16,000 fps. Images a and b, respectively, show the halo emissions at t=0.750 and 1.125 ms, between which the halo structure descends with an average downward speed of 6.4 × 106 m s−1. Image c shows the sprite streamer initiated from the descending spatial structure. Panel d shows a 1.875-ms image time series of the halo structure and streamer development.