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 (∼10 4 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]. Copyright 2002 by the American Geophysical Union.