Weather Library > Sferics - Radio Lightning Detection

By DAN ROBINSON

Editor/Photographer

Lightning doesn't only make light and sound. The discharges also produce radio waves called sferics. Chances are you've heard them on the radio while listening to a baseball game or talk show on a somewhat distant AM station. Sferics play a large role in lightning detection and mapping device technology currently in use around the world.

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Listen to Sferics

The following are short clips of sferics in MP3 format recorded directly off of an AM radio during thunderstorms:

Sferic 1 - Lightning discharges, less than 5 miles away.

Sferic 2 - Lightning discharge, estimated 30 miles away.

Sferic 3 - Lightning discharge, estimated 60 miles away.

Sferic 4 - Lightning discharge, estimated 60 miles away.

Sferics also occur apart from thunderstorms. The crackling sound on an A.M. radio from a nearby power tool, hair dryer, or any motorized appliance are radio waves from the sparks in the motor. Sferics can also be heard on some car radios from the spark plug discharges in the engine.

Sferics can turn any AM radio into a simple lightning detection device. They are easily distinguished from normal static in that they are sudden loud, crackling noises, sounding a little like someone wringing a wad of plastic bubble wrap. They occur simultaneously with any lightning discharge. Especially at night, your AM radio can pick up waves from lightning hundreds of miles away.

AM Radio Detection Tips

Tune to a frequency with weak or nonexistent reception. Your radio will not be as sensitive to sferics if it is tuned to a station that is receiving clearly.
The volume and sound of the sferics will be different depending on how far away the lightning is. Faraway lightning will sound somewhat muffled and smoother, wheras closer lightning (within 40 miles or so) will be louder and contain distinct popping sounds.

Family Activity - Lightning Radio

The next time your family vacation drive takes you near or through a thunderstorm, turn on the AM radio. See if you can identify the sferics and estimate the distance to the lightning that created it. Watch for the flashes in the sky while you hear them on the radio at the same time.