Submillisecond imaging of sprite development and structure

We report intensified high speed video observations of two mesospheric transient luminous events acquired at 5000 and 7200 frames per second. Downward streamers appear to initiate either spontaneously or from brightening inhomogeneities at the bottom of a halo, and branch as they propagate downward. Simultaneously, a brighter column expands upward and downward from the initiation point. This expansion is usually followed by the development of bright upward propagating streamers that originate from the bottom of the expanding bright column and that terminate in diffuse emissions. The lower portions of these upward streamers are typically brighter and more persistent and form the bright core of the sprite. A new phenomenon is observed in which the tips of downward-moving sprite streamers are attracted to and, in some cases, collide with adjacent streamer channels. The points of streamer collision appear to become long-persisting sprite beads, which have been suggested previously to affect mesospheric chemistry. Other persistent beads appear to form spontaneously on the downward streamer channels near the lower edge of the bright upper portion of the sprite.