Aug 15, 2000 - "cloud-to-space lightning" might pose a threat to Space Shuttle missions during launch or recovery Based upon the then-available evidence ...
Eos,Vol. 81, No. 33, August 15, 2000 EOS,
T R A N S A C T I O N S ,
A M E R I C A N
G E O P H Y S I C A L VOLUME 81
U N I O N
NUMBER 33
AUGUST 15, 2000 PAGES 373-380
of Minnesota, led by John R.Winckler, were testing a low-light camera system (LLTV) for an upcoming rocket flight when, quite by accident, they captured two fields of video that provided the hard evidence for what are now called sprites [Franz et al, 1990]. From this singular observation emanated a decade of fruitful research into the electrodynamics of the middle atmosphere. The sprites occurred several milliseconds after especially energetic discharges within the storm cells which, while larger than their neighbors, had otherwise unexceptional flash rates. By 1993, the NASA Shuttle Safety Office developed concerns that this newly discovered "cloud-to-space lightning" might pose a threat to Space Shuttle missions during launch or recovery Based upon the then-available evidence, the hunt for these elusive events was directed above the stratiform regions of large mesoscale convective systems (MCSs),
The Hundred Year Hunt for the Sprite PAGES 373-374,376-377 The scientific community's perception of the middle atmosphere above thunderstorms as "uninteresting" changed completely in the last decade.Today, a host of lightning-related Tran sient Luminous Events (TLEs) have been identified, including sprites, blue jets, elves, sprite halos,and trolls. Others may remain to be discovered. Aside from the intrinsic scientific issues arising from this linkage of tropospheric electrical phe nomena with that of middle atmosphere, a num ber of practical questions emerge.Whatjf any threats might TLEs pose to aerospace operations above 20 km? Do sprites represent a heretofore undocumented source of middle atmospheric No ? What role might they play in the global electrical circuit, as well as in the energetics of the upper atmosphere [Bering et ai, 1998]? Might these phenomena impact satellite-based global monitoring and surveillance efforts?
these were documented by Otha H.Vaughan at NASA Marshall Space Flight Center and the late Bernard Vonnegut at the State University of New York at Albany The observations shared one common characteristic: they were perceived as highly atypical of "normal" lightning. The reaction of the atmospheric science commu nity could be summarized as indifference at best.Then, as so often happens in science, serendipity intervened.
H a r d Evidence The air of mystery began to dissipate at 0414 UTC on July 6,1989. Scientists from the University
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Curiously, given the recent flurry of investiga tions, over a century has elapsed since the first published reports of TLEs. Since 1886, dozens of eyewitness accounts of TLEs, mostly in obscure meteorological publications, have been accompanied by articles describing meteorological esoterica such as toads falling from the sky during rain showers. A typical description might read,"In its most typical form it consists of flames appearing to shoot up from the top of the cloud or, if the cloud is out of sight, the flames seem to rise from the horizon." Science often advances at a deliberately cautious pace and such reports were largely ignored by the nascent atmospheric electricity community—even when they were posted by a Nobel Prize-winning physicist. As early as 1925, C.T. R.Wilson proposed mechanisms to explain such phenomena. In 1956,Wilson commented,"It is quite possible that a discharge between the top of the cloud and the ionosphere is a normal accompaniment of a lightning discharge to earth...a diffuse discharge between the top of the cloud and the upper atmosphere...many years ago I observed what appeared to be discharges of this kind from a thundercloud...they were diffuse, fan-shaped flashes...extending up into a clear sky" Over the next 3 decades, many similar sub jective observations from credible witnesses worldwide were reported. During the 1980s,
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