Effects of thunderstorm activity on the upper atmosphere and ionosphere: special issue of the Journal of Atmospheric and Solar-Terrestrial Physics

It has been less than ten years since the paper by Franz, Nemzek and Winckler (1990) appeared showing the first images of optical emissions excited in the high atmosphere by thunderstorms. C. T. R. Wilson had hypothesized many years before on general theoretical grounds that ``upward lightning'' ought to occur in the rarefied atmosphere above a thunderstorm. However, evidence for such effects remained elusive until Franz et al. captured the first optical signatures using low light level video instruments. Their results spurred a follow-on search of Space Shuttle video tapes, where more than a dozen transient pillars of light were detected above thunderstorms on the limb of the planet as viewed from space, verifying the existence of the phenomena on a global scale. Beginning in July and August of 1993, and with growing vigor in succeeding summers, there has occurred a very large increase in the number and quality of low light level video observations, both from the ground and from aircraft, of what have become known as ``red sprites'', ``blue jets'', and ``elves''. Optical images have revealed a phantasmagoria of sprite forms, with events stretching horizontally over tens of km. In their totality the events span the full distance between the troposphere and the ionosphere. The durations of the events are very short, ranging from sub-millisecond for elves to a few- to tens-of-milliseconds for sprites and 100s of milliseconds for blue jets. Measurements of the electromagnetic emissions accompanying the events have shown effects from the ULF into the VLF. Satellite measurements of millisecond gamma ray bursts originating from thunderstorm systems and their correlation with discrete VLF signatures suggest that these events, too, may derive from processes creating the optical emissions. The present issue of the Journal of Atmospheric and Solar-Terrestrial Physics is the first Special Issue devoted to the field of upper atmospheric electrical effects excited by lightning. Approximately two dozen contributions have been made by many of the same researchers who have been actively laying the observational and theoretical foundations for this new field over the past several years. The papers provide a good mix of historical reviews with new observational and theoretical results, and represent in capsule form the state of understanding as of 1996-1997. However, the field is evolving rapidly, with each fresh thunderstorm season yielding new measurements across a wideni