Observations of streamer formation in sprites

Abstract

Sprites have been recorded at 10,000 fps with 50 μs 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 μs 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 106 and 107 m/s. Both positive and negative accelerations, of magnitude 105 - 1010 m/s2, 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. Copyright 2007 by the American Geophysical Union.