Polar Waves: One Cool Sound

Our SoundClips series continues with listener Jim Hetrick of Stockton, Calif. He shares recordings he made in 1982 at the South Pole, where he captured low-frequency radio waves created by lightning storms.

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Today's installment of our SoundClip series comes from the other end of the Earth, the South Pole.

(Soundbite of radio wave frequency)

Dr. JIM HETRICK (Physics Department, University of the Pacific): My name is Jim Hetrick. I live in Stockton, California, and I'm the chairman of the physics department at the University of the Pacific.

(Soundbite of radio wave frequency)

Dr. HETRICK: The sound that you're listening to is a very low frequency radio wave. I recorded it at the South Pole in 1982.

(Soundbite of whistler)

Dr. HETRICK: I was there for 13 months studying cosmic rays, the auroras, the Earth's magnetosphere, the solar wind, the interaction between all of these.

(Soundbite of whistler)

Dr. HETRICK: The sound that you hear is called a whistler. It's produced by a lightning flash that's somewhere in the northern hemisphere. When a lightning flashes, it creates radio waves at all different frequencies. And some of those propagate upward and get in to the magnetosphere of the Earth and travel along the magnetic field lines, and end up in the southern hemisphere. But along the way, the pulse - the radio pulse gets distorted. It suffers what we call dispersion, which means that the lower frequency waves travel significantly slower than the high frequency waves. So the original pop gets stretched out, the highest frequencies arrive first followed by kind of an avalanche of lower and other frequencies.

(Soundbite of whistler)

Dr. HETRICK: The radio waves that your car radio receives are at much higher frequency. These radio waves are in the audio range already. And so all you have to do is detect the radio wave and send it to a speaker, amplify it.

(Soundbite of radio waves)

NORRIS: Listener Jim Hetrick of Stockton, California with naturally occurring radio waves collected at the South Pole. Find out more about our series at our Web site, npr.org. Look for the word SoundClips.

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