No. 90: Nov-Dec 1993
Past issues of Science Frontiers have recorded several examples of anomalous luminous phenomena above cloud tops (in SF#89, for example). Almost all of these observations have been anecdotal and too qualitative to be of use to scientists. Happily, some atmospheric scientists are now taking more interest in "rocket lightning" and those strange light flashes seen above storm clouds. First, though, one more anecdotal report, and then we'll summarize two recent scientific efforts to elucidate these phenomena.
July 28, 1993. 150 miles south of Panama. From an aircraft flying at 33,000 feet.
"I and another pilot in the cockpit of American Airlines Flight 912 were watching and circumnavigating a large cumulonimbus cloud. About five times, a large discharge of lightning at the top of and within the cloud was followed by a vertical shaft of blue light that propagated from the top of the cloud upward to 100,000 ft.
"The beam was very straight and the color distinctly different from the lightning. At the top of this shaft, the column fanned out just before its disappearance. All the occurrences were identical. At least one also was witnessed by three other American pilots about 30 min. behind us on the same route."
(Hammerstrom, John G.; "Mystery Lightning," Aviation Week, 139:6, August 30, 1993. Cr. J.S. Denn and D.K. Hackett.)
July 1993. From an aircraft over the American Midwest. E. Wescott and D. Sentman, employing a very sensitive camera aboard a NASA DC8, recorded 19 unusual flashes over a thunderstorm. Each flash lasted less than 1/30 second.
"The scintillations are estimated to be about 25 miles tall, 6 miles wide and more than 240 cubic miles in volume, according to Eugene Wescott and Davis Sentman.
"Their shapes resemble resemble jellyfish, Wescott said. 'They appear brightest where they top out, typically about 40 miles high, so you have the jellyfish body at the top with tentacles trailing down.'"
The nature of these flashes is unknown. Wescott and Sentman ventured that they might be a type of glow discharge. (Sawyer, Kathy; "NASA Captures Image of Mysterious 'Jellyfish" Flash," Washington Post, September 24, 1993. Cr. S. Reyes. Shorter versions of the Post article also appeared in the Philadelphia Inquirer, September 25, 1993. Cr. T. Shelton. Also: the Dallas Morning News, September 24, 1993. Cr. L. Anderson.)
September 22-23, 1989. Southeastern North America. Anomalous flashes were detected above Hurricane Hugo by Minnesota-based SKYFLASH equipment. Hurricanes, of course, are accompanied by thunderstorm activity.
Said apparatus consists of three photmetric telescopes using photomultiplier tubes with 19-inch parabolic mirrors. A variety of light pulses appearing in the night sky have been recorded during SKYFLASH surveys. The most puzzling types of flashes were the "long" events, which lasted about 20 milliseconds, with slow rises and falls. During the "long" flashes, no sferics (radio disturbances) are detected, whereas the more common shorter flashes are accompanied by sferics. However, during Hurricane Hugo, these mysterious "long" flashes occurred much more frequently than usual. The origin of the "long" flashes remains unknown. (Winckler, J.R., et al; "Fast Low-Level Light Pulses from the Night Sky Observed with the SKYFLASH Program," Journal of Geophysical Research, 98:8775, 1993.)
Comment. The "light rays," the "jellyfish," and the "long" flashes may be different aspects of the same phenomenon. In any case, some sort of unrecognized electrical activity is transpiring between storm-cloud tops and the ionosphere.
Reference. "Rocket lighting" and other unusual electrical discharges are cataloged in: Lighting, Auroras. To order, visit: here.
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