No. 94: Jul-Aug 1994
"Mysterious double bursts of radio emissions, originating near the surface of the earth, have been detected by a small satellite designed to spot nuclear blasts.
"Although the powerful pulses of electromagnetic energy occur predominantly at times of day favored by thunderstorms, they are not accompanied by flashes of visible light and they do not resemble the emissions generated by classic lightning."
Since November 5, 1993, about 100 of these bursts have been detected by a special radio receiver named "Blackbird" mounted on the Alexis satellite. Most of the bursts have been recorded over Africa and South America, although they may also be frequent elsewhere but are drowned out by man-made radio noise from the ground.
The bursts come in pairs that are separated by 40 microseconds. The frequency dispersion of the bursts indicates that the signals have passed through the earth's ionosphere before reaching the satellite. Most bursts are picked up in the afternoon and early morning.
There is some speculation that the bursts may be associated with the flashes of light recently reported above storm systems. (SF#90)
(Quote from: Sawyer, Kathy; "Electrodynamics: Strange Bursts from the Sky," Washington Post, February 14, 1994. Also: Monastersky, R.; "Puzzling Atmospheric Bursts Spark Interest," Science News, 145:100, 1994. Hecht, Jeff; "Satellite Tunes in to Mystery Radio Bursts," New Scientist, p. 7, February 26, 1994.)