A survey of streamer and diffuse glow dynamics observed in sprites using telescopic imagery

Abstract

While the fine structure in sprites can assume a wide variety of shapes, sizes, and timescales, certain patterns such as upward branching, downward branching, beading, columns, bidirectional streamers, and propagating large‐scale diffuse glow regions are repeatedly observed. Example cases of these streamer and diffuse glow dynamics observed in sprites are presented using video data obtained by a telescopic imaging system in July–August 1998 and are compared to predictions of current sprite and streamer theories. The previously unreported propagating diffuse glows move slowly (∼104 m/s) and are broader than that predicted for a streamer formation at the same altitude. Sudden brightening of slowly developing negative streamers may be indicative of a return stroke process in which the streamers connect with charge in a lowered ionosphere. Meteoric dust particles in the upper atmosphere may be responsible for the fine beading that exists in many negative streamers and may cause plasma enhancements that initiate double‐headed streamers. Beads at the base of columns can glow for over 100 ms while slowly drifting upward (∼104 m/s). Columns may initiate from downward branching positive streamers. Faint positive streamers are observed at the base of and/or preceding large bright sprite events. Some sprites may initiate as double‐headed streamers formed in localized regions of enhanced electron density. A transition between the streamer formation region and the diffuse glow region is observed at ∼80‐km altitude. No fine structure is observed in telescopic images of the diffuse glow region also referred to as the “sprite halo” [Barrington‐Leigh and Inan, 2001].