- Auroral kilometric radiation
Auroral kilometric radiation (AKR) is the intense radio
radiationemitted in the acceleration zone (at a height of three times the radius of the Earth) of the polar lights. The radiation mainly comes from cyclotron radiationfrom electronsorbiting around the magnetic fieldlines of the Earth. The radiation has a frequencyof between 50 and 500 kHz and a total power of between about 1 million and 10 million watts. The radiation is absorbed by the ionosphereand therefore can only be measured by satellitespositioned at vast heights, such as the Fast Auroral Snapshot Explorer (FAST). According to the data of the Cluster mission, it is beamed out in the cosmos in a narrow plane tangent to the magnetic field at the source. The sound produced by playing AKR over an audio device has been described as "whistles", "chirps", and even "screams".
As some other planets emit cyclotron radiation too, AKR could be used to learn more about
Jupiter, Saturn, Uranusand Neptune, and to detect extrasolar planets.
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