Not much has been published (to my knowledge) about sferics, so this section is based on my observations and not on any proven facts.
What are sferics?
Sferics are the radio waves produced by the current-carrying lightning channel. They are easy to hear...just turn on any A.M. radio when there is thunderstorm activity in your area. (Tune the radio to where you don't pick up any broadcasts, you will hear the sferics more clearly) They are easily distinguished from static in that they are sudden loud, crackling noises, occuring simultaneously with any lightning discharge. Even if you can't see lightning, the radio will pick up even distant lightning discharges. Sferics occur in everyday life, too. The crackling sound on an A.M. radio from a nearby power tool, hair dryer, or any motorized appliance is due to the sferics from the sparks in the motor. Sferics can also be heard on a car radio from the spark plug discharges in the engine.
How can sferics be useful?
Sferics can be used to make your radio a simple lightning detector, alerting you to nearby thunderstorm activity.
Sferics could be a useful tool in the study of lightning. The crackling noises are descriptive of the discharge that caused them- for instance, a flash with many return strokes will sound as a series of pulsating crackles. Every lightning discharge, or every static discharge, will produce radio waves, so every lightning flash nearby will produce a crackle on the radio. The further the lightning flash is from the radio, the fainter the crackle, the closer the flash, the louder and more pronounced the crackle. In other words, the volume of the crackle is inversely proportional to the distance between the lightning flash and the radio. This means it could be possible to develop an inexpensive detection system to determine the distance to the flash by using some sort of sensor that would measure the volume of each crackle and calculate the distance to the lightning flash. Furthermore, by using three or more of these 'sensors' it would be possible to accurately locate the spot where the flash occured.
There is a national lightning detection system in place today that records the exact location of every cloud-to-ground lightning flash in the U.S.. I don't know the method this detection system uses, but it may be with sferics as described above.
All information above is based on observations only, and should not be used as a fact in a report unless it is stated as theory.
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