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Environment

#93: Physicists Discover the Source of Earth’s "Mystery Hiss"

A strange electromagnetic wave follows the path of sound waves through water.

By Susan KruglinskiDecember 5, 2008 6:00 AM

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For 40 years engineers and physicists have puzzled over “the hiss,” a mysterious electromagnetic wave surrounding the earth that, when played through a loudspeaker, sounds like the hissing and swishing between tracks on a scratchy vinyl record. In March UCLA physicists reported that the hiss may start its existence as a wave called “the chorus,” which has long been seen as entirely unrelated to the hiss.

The effects of the hiss and the chorus are well known to NASA scientists. The hiss occurs throughout the plasmasphere (the zone thousands of miles above the earth that teems with ionized gases), removing the plasmasphere’s high-energy electrons and tempering their lethal power. Thousands of miles beyond the hiss, outside the plasmasphere, is a vastly different kind of electromagnetic wave, the chorus. Through a speaker the chorus sounds like a choir of birds chirping and whooping in a rookery. The chorus does the opposite of the hiss, producing dangerous high-energy electrons.

Jacob Bortnik, a space physicist at UCLA, was studying the chorus phenomenon when he stumbled upon the idea that it might leak into the plasmasphere. In his model, as the chorus makes its way into the plasmasphere, the wave devolves into the hiss in the same way that a full-bodied song from a radio becomes a mush of dull notes when the sound waves travel through water. If Bortnik’s model is verified, it may improve NASA’s understanding of the earth’s upper atmosphere. High-energy electrons can damage spacecraft and satellites and can even harm astronauts doing work outside their craft.

“Space scientists need to understand the hiss to predict radiation in the upper atmosphere,” Bortnik says. “We have 40 years of observations of the hiss, so now with this model we can really understand its characteristics.”

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