Observations of streamer formation in sprites

Sprites have been recorded at 10,000 fps with 50 μ s image exposure time. At this time resolution it is possible to resolve the temporal development of streamer tips. The recordings show that sprites start with a streamer head forming at an altitude near 80 km. The streamer head moves rapidly downwards while brightening, and ∼300 μ s after streamer passage longer lasting emissions ensues. This is essentially the C‐sprite. In some events upward moving streamer heads are also observed, in which case we have a carrot‐sprite. The streamer speeds vary between 10 6 and 10 7 m/s. Both positive and negative accelerations, of magnitude 10 5 – 10 10 m/s 2 , were observed. Upward streamers, when present, always start later and from a lower altitude than downward streamers, and they start from existing structure in the sprite.