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.
Why do people listen? For the same reasons we watch whales, the sunset over the ocean, brave the cold to see the Northern Lights, fight the mosquitoes to see a meteor shower and so on. We like to experience the awe and mystery of creation. But there are scientific reasons for these observations also. Before satellites were common, whistlers taught us a great deal about the nature of the ionosphere and the magnetosphere.
While the bulk of natural Radio signals occur at VLF Frequencies or lower, any radio signal that emanates from lightning or any other natural process can be classified as Natural Radio, no matter what the frequency.
As we become more and more dependent on satellites for communication and earth observation, the study of “Space Weather” and the ionosphere and magnetosphere will become increasingly important. As we gain a greater understanding of the earth-sun connection we will realize how activity on the sun can affect weather patterns here on earth. This will be relevant as we study the causes of global warming. We are just beginning to see how the cycles of the sun affect our weather here.
So please explore this site. And I hope you go beyond reading what’s here and actually go out and take the opportunity to hear whistlers or the enchanting sounds of the dawn chorus.
Mark Karney, N9JWF