The earth is alive with its own radio broadcasts. Lightning, the solar wind and solar storms create a variety of radio signals that surround us and lie just beyond our reach. They lie just beyond our perception because although their frequencies fall within the range of human hearing, they are radio waves that our ears don't perceive. But the simplest of receiving equipment will allow you to hear them. Just hook an antenna to any high-gain audio amplifier and these hidden signals will become audible.

What will you hear? First of all, atmospherics or "sferics" for short. These are the radio waves generated by lightning and sound very much like the radio static you hear when there are thunderstorms in the area. You'll be able to hear sferics almost all of the time.

The next signal you might hear is a "tweek". Tweeks are usually heard at night and are spherics that have traveled a long distance and have a resonant "twangy" sound. You can probably hear tweeks on almost any night.

Whistlers are more rare. They originate from lightning and sound like a descending tone or a descending "swoosh" and may last several seconds. Whistlers can occur at any time of day but are most often heard in the pre-dawn hours.

There are many more sounds that are often grouped together under the term "VLF Emissions", VLF being Very Low Frequency. These sounds originate in the magnetosphere and are the result of disturbances originating from the solar wind and geomagnetic storms. These sounds are most often heard before and for several hours after sunrise, especially during geomagnetic storms.

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