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Tune in to noise out.

Tune in to noise out

Just before the silence of space begins in the outer reaches of the earth's atmosphere is a region that shimmers with sound. The symphony of signals found in the magnetosphere-- where the geomagnetic field has trapped a plasma of charged particles--include whistle-like noises triggered by lightning and the chirping sound of the "chorus' created when an incoherent set of radio waves passes through.

Radio scientist Robert Helliwell at Stanford University and his colleagues have also shown that a radio signal at one frequency sent into the magnetosphere will grow and trigger a noisy rainbow of signals at slightly different frequencies. Now the researchers find that the magnetosphere will produce a series of signals at discrete frequencies when radio waves of two or more frequencies are transmitted from their research station in Antarctica.

For example, a transmitted signal oscillating at 2,000 hertz (hz) and another at 2,030 hz results in a "subharmonic' signal at 2,015 hz, as well as other signals at 2,060 hz and 2,090 hz. These signals are often just as strong as the waves received at the injected frequencies. "The mechanism for their generation is not yet understood,' says Helliwell, "but their presence indicates an interesting process at work . . . that may play a role in creating the kind of observed noise we see in the magnetosphere.' It's possible, adds one co-worker, that the zoo of odd noises may arise from rather simple combinations of waves.
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Title Annotation:noise in the magnetosphere
Author:Weisburd, Stefi
Publication:Science News
Date:Jun 7, 1986
Words:247
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