Electrical Discharges into the Stratosphere from the Tops of Intense Thunderstorms
Abstract
The serendipitous capture by John R. Winckler in July 1989 of the first low-light video of what are now called sprites launched a new era of middle atmospheric electrodynamic research. Since then, over 10,000 mesospheric sprites have been imaged by teams worldwide. Initially termed cloud-to-stratosphere (CS) lightning, this name was wisely abandoned because it implied more than was confirmed about the physics of the phenomenon. Sprites, almost exclusively associated with positive cloud-to-ground lightning (+CG) flashes possessing very large charge moments (500 C*km and up), occur within the stratiform regions of large mesoscale convective systems (MCS). In searching for sprites above MCS, other phenomena, now collectively termed transient luminous events (TLEs), were discovered, including elves, halos and trolls. The sprite, elve and halo optical emissions all occur well above the tops of even the tallest storms. The blue jet was the first TLE found that emerged from the top of the parent storm. The more recently discovered (red) trolls represent a faint discharge from or near the cloud tops returning up the channel of the previously intense sprites having unusually long tendrils. None of these TLEs could be termed true "cloud-to-stratosphere" lightning. Yet an examination of over a century of scientific literature frequently yields descriptions though while not matching any of the known TLEs would suggest a true CS event. Numerous eyewitness reports suggest long-lasting, brilliant lightning-like discharges can propagate from the tops of certain storm cells, at times to estimated heights of 35 km. Film images of 3 such events initially thought to be blue jets may represent the CS - which we have tentatively given a new name, "gnomes." On 22 July 2000, during the STEPS program, a GEN III ultra-blue extended imager at Yucca Ridge was monitoring distant sprites when a nearby supercellular storm entered the field of view. Distinctive "discharges" were detected on the cloud top. Several dozen appeared as bright, very small (sub 100 meter?) and very brief (sub 16ms) "dots." Another dozen or more exhibited upward propagation on the order of 1- 2 km. While having certain features in common with blue jets, they were also optically much brighter and narrower. The "gnomes" occurred for 20 minutes at the base of an overshooting convective dome during the supercell's growth stage. The "gnomes" were not associated with either CG or IC flashes. The storm's IC and CG lightning flash temporal and spatial distribution statistics suggest atypical behavior.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFMAE22A..02L
- Keywords:
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- 3304 Atmospheric electricity