Natural Radio: Whistlers: The Pulse of the Planet daily radio program offers free legal online mp3 downloads, exploring the world of sound in nature, culture and science, with audio adventures, world music, extraordinary sound portraits, science diaries, and nature ring-tones; an amazing sonic experience.

Airdate: Mar 17, 2003
Scientist: Stephen McGreevy

Natural Radio: Whistlers

Natural Radio: Whistlers
Radio waves created by lightning can be heard from halfway around the planet.

ambience: electromagnetic radiation/whistlers

During World War I, a German scientist trying to eavesdrop on allied telephone conversations kept picking up strange whistling noises on his equipment. Well, Eventually these sounds were identified as being caused by lightning coming from as far away as halfway around the world. I'm Jim Metzner, and this is the Pulse of the Planet.

The sounds were ultimately named whistlers and today, with the help of a long antennae and a special receiver, Steve McGreevy records whistlers and other electromagnetic waves which occur naturally in our planet's atmosphere.

"The ever present thing which we're always hearing is the snapping and crackling and popping of lightning strikes. That's just a constant background noise."

Along with the cracks and pops, you can hear the distinctive sounds of whistlers, those long, descending tones. Now, whistlers originate from the electromagnetic waves which are generated during lightning storms. These waves are guided by the lines of force which make up the Earth's magnetic field. Following the lines of force, the waves circle the Earth in a matter of seconds, and when you tune in with a radio receiver, you can hear them as trailing, whistling sounds.

"What happens is the energy takes a round trip in Earth's magnetic field to the opposite hemisphere and then it bounces back. And in doing so, in making this long trip, the frequency components are spread out. In other words, the instantaneous bursts of lightning gets peeled apart; the higher audio frequencies arrive, the higher audio frequencies arrive before the lower ones. So you get this downward falling tone."

Pulse of the Planet is presented by the National Science Foundation. I'm Jim Metzner.