HR: 0800h
AN: AE31B-0172    [Abstracts]
TI: Observations of Quasi-Planar Ionizing Solitary Waves Associated With Sprites
AU: * Sentman, D
EM: dsentman@gi.alaska.edu
AF: University of Alaska, Geophysical Institute University of Alaska, Fairbanks, AK 99775 United States
AU: Stenbaek-Nielsen, H
EM: hnielsen@gi.alaska.edu
AF: University of Alaska, Geophysical Institute University of Alaska, Fairbanks, AK 99775 United States
AU: Bering, E
EM: ebering@mail.uh.edu
AF: University of Houston, Department of Physics 617 Science and Research I, Houston, TX 77204 United States
AB: The University of Alaska performed a series of optical sprite observations from the Wyoming Infrared Observatory (WIRO) on Jelm Mountain as part of the Sprites99 field campaign. One of the cameras was a white light 1000 frame/sec high speed imager (HSI) that permitted following sprite dynamics at millisecond time scales and spatial resolutions of a few hundred meters. A number of sprites exhibiting a variety of complex forms over a wide range of brightness were recorded the night of 18 August 1999 over a very active thunderstorm centered over nearby Nebraska, ~300 km from WIRO. An analysis of contrast enhanced images of sprites from this storm revealed a previously unreported type of weak (~several hundred kR), diffuse emission associated with most events. In time lapse sequences the diffuse emissions give the visual appearance of downward expanding puffs of smoke launched from the bottom ends of streamer tendrils at ~60 km altitude, reaching diameters ~ 5-10 km over ~5-10 ms, for an average apparent expansion speed of ~ 1000 km/sec. Several of the events clearly exhibited an effect analogous to limb brightening, suggesting the emissions originated in expanding shells of ~1-2 km thickness. Other events, unaccompanied by immediate streamers, were observed to originate near 75 km and propagate downward as quasi-planar sheets of weak optical emissions. It is proposed that these emissions are the optical signatures of large scale, ionizing solitary waves excited in the upper atmosphere by transient quasi-electrostatic lightning electric fields, and which propagate downward as shells or sheets of electric charge. A one-dimensional fluid model of ionizing solitary waves is developed appropriate to the weakly ionized collisional plasma environment of the upper atmosphere. Both negative and positive charge density solitary waves may occur, depending on the polarity of the applied transient electric field. The solitary waves propagate as thin, self-consistent charge structures at speeds typically much larger than the electron drift speed. It is found that electron attachment processes play a strong role in determining both the internal charge structure of the solitary wave and the plasma composition in its trailing wake. When taken in combination with streamers, which may be thought of as thin columnar versions of ionizing solitary waves, such events may help account in part for the enormous spatial complexity that typically characterizes sprites. It is suggested that some of the puzzling features of ELF/VLF electromagnetic emissions associated with sprites may derive from charge transport by ionizing solitary waves.
DE: 3324 Lightning
DE: 2716 Energetic particles, precipitating
DE: 3304 Atmospheric electricity
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting