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Science Frontiers ONLINE No. 95: Sep-Oct 1994 |
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Gamma-ray flashes in the upper atmosphere
Something strange is definitely going on in the upper atmosphere, particularly above thunderstorms. We have already reported on the mysterious light flashes (SF90) and radio emissions (SF#94). Now, we record similar, possibly intimately related flashes of energy in a different portion of the electromagnetic spectrum.
"Detectors aboard the Compton Gamma Ray Observatory have observed an unexplained terrestrial phenomenon: brief, intense flashes of gamma rays. These flashes must originate in the atmosphere at altitudes above at least 30 kilometers in order to escape atmospheric absorption and reach the detectors."
The energies of the gamma rays in the flashes are very high. They are typical of the braking radiation (Bremsstrahlung) from 1,000,000 electron-volt electrons. Since most of the gamma flashes originate over regions where thunderstorms are frequent, it is tempting to associate them with lightning. Ordinary lightning, however, is not energetic enough to generate the gamma flashes and, of course, it does not occur above 30 kilometers altitude anyway. G.J. Fishman et al, who reported on this new phenomenon in Science, speculate that some hitherto unrecognized, high altitude electrical discharges occur high above areas hosting thunderstorms. Possibly, upwardly directed lightning ("rocket lightning") is involved in all three of the newly found flashes in the radio, optical, and gamma portions of the electromagnetic spectrum.
(Fishman, G.J., et al; "Discovery of Intense Gamma-Ray Flashes of Atmospheric Origin," Science, 264:1313, 1994. Kerr, Richard A.; "Atmospheric Scientists Puzzle Over High-Altitude Flashes," Science, 264:1250, 1994.)