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Sudden sodium surges seen over Illinois.

Sudden sodium surges seen over Illinois

Clouds of sodium atoms that rapidly appear and then disappear have been detected high in the sky over Urbana, Ill. While it may seem strange that the vanishing clouds have been noticed only over that city, scientists from the University of Illinois who observed the phenomenon say they are not really perplexed, because they have the only machine that can detect the sodium clouds, which are probably coming from meteors as they burn up in the atmosphere.

Timothy Beatty and colleagues observed the clouds with a lidar -- an instrument that sends laser pulses up into the atmosphere and measures the light that returns. Several features make the lidar in Urbana unique. The laser pulses about 200 times a second, which is 10 to 20 times more frequent than most lidars. Moreover, the Urbana lidar employs an unusually sensitive light-detection system with a telescope to gather incoming photons. Sodium atoms high in the atmosphere absorb the laser light and then emit much fainter radiation at a telltale wavelength that the detector picks up.

On at least five occasioins the Urbana group found sudden surges and then drops in the concentration of sodium atoms at an altitude of around 85 kilometers, Beatty and colleagues report in the September GEOPHYSICAL RESEARCH LETTERS. Beatty suggests the clouds are vaporized meteor material, and his group expects to tune the lidar to detect other meteoric elements such as iron and calcium. All three elements exist in small concentrations at this altitude and are believed to be supplied by meteors.
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Publication:Science News
Date:Oct 8, 1988
Words:259
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