SUPERCELLS AND SPRITES

SUPERCELLS AND SPRITES Over a decade of monitoring mesospheric transient luminous events (TLEs) above U.S. high plains storms confirmed sprites are almost exclusively associated with positive polarity cloud-to-ground lightning (CGs). Following C. T. R. Wilson's theory proposed in 1925, only those CGs lowering large amounts of charge to ground should induce sprites. The key metric, the charge moment change, generally must exceed ~600 C km to initiate the electric breakdown at 75 km, which evolves into the sprite. High plains storms generate the highest percentage, the largest average peak current, and highest density of CGs in the nation. Various storm types generate CGs, and especially supercells are often dominated by positive strokes. Few sprites observations above supercells have been obtained (and usually during their decaying phase), while thousands of sprites have been imaged above mesoscale convective system (MCS) stratiform regions and some squall lines. During the 2000 Severe Thunderstorm Electrification and Precipitation Study (STEPS), two supercells were examined. One storm contained >90 CGs, but none exceeded the sprite charge moment change threshold. A second nocturnal supercell did produce sprites from the last two CGs of the storm as a stratiform region developed, more favorable for significant continuing currents to follow the CG return stroke. Unexpectedly, three sprites occurring during the most intense phase of the storm were triggered by unusually intense and impulsive CGs, which lowered sufficient charge in the return stroke alone for sprite initiation. Such CGs, and thus sprites, are probably relatively rare events during the supercell mature stage. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Bulletin of the American Meteorological Society American Meteorological Society

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0477
D.O.I.
10.1175/2008BAMS2439.1
Publisher site
See Article on Publisher Site

Abstract

Over a decade of monitoring mesospheric transient luminous events (TLEs) above U.S. high plains storms confirmed sprites are almost exclusively associated with positive polarity cloud-to-ground lightning (CGs). Following C. T. R. Wilson's theory proposed in 1925, only those CGs lowering large amounts of charge to ground should induce sprites. The key metric, the charge moment change, generally must exceed ~600 C km to initiate the electric breakdown at 75 km, which evolves into the sprite. High plains storms generate the highest percentage, the largest average peak current, and highest density of CGs in the nation. Various storm types generate CGs, and especially supercells are often dominated by positive strokes. Few sprites observations above supercells have been obtained (and usually during their decaying phase), while thousands of sprites have been imaged above mesoscale convective system (MCS) stratiform regions and some squall lines. During the 2000 Severe Thunderstorm Electrification and Precipitation Study (STEPS), two supercells were examined. One storm contained >90 CGs, but none exceeded the sprite charge moment change threshold. A second nocturnal supercell did produce sprites from the last two CGs of the storm as a stratiform region developed, more favorable for significant continuing currents to follow the CG return stroke. Unexpectedly, three sprites occurring during the most intense phase of the storm were triggered by unusually intense and impulsive CGs, which lowered sufficient charge in the return stroke alone for sprite initiation. Such CGs, and thus sprites, are probably relatively rare events during the supercell mature stage.

Journal

Bulletin of the American Meteorological SocietyAmerican Meteorological Society

Published: Aug 17, 2008

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