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I drove through a Wyoming thunderstorm today. Just for fun, I set my AM car radio to the top end of the AM broadcast band where there was no station audible. Sure enough, I heard the lightning crashes, some of which were visible.

However, occasionally there would be a deep growling sound that would last a full second or more, not correlated with anything I could see in the sky. I have never heard such a thing before, and I strongly suspect that it is an electrical effect of the storm. The effect happened mid-afternoon, before AM radio propagation goes DX, so I know it was local. I found the same noise at the low end of the AM broadcast band.

What are the possible sources of this radio noise? Can it be duplicated in a laboratory?

richard1941
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1 Answers1

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Assume 100 hertz for the growling. Or 10 millisecond period. Or 10,000 us period.

Electricity travels 1 mile in 5 microseconds. thus this was a 2,000 mile event.

Could be the local charges getting replaced, from 2,000 miles way.

Lightning requires cosmic-ray energy; approx. 70 amps per second worldwide average current from outer space, per Feynman.

That current needs to make its way, from all around the world, to the various storms dumping change down onto the ground.

Thus, if this is correct, your storm was getting replenished from 2,000 miles away.

winny
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analogsystemsrf
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  • I suspect the growl is just the AGC with lots of inter cloud lightning. – Tony Stewart EE75 Sep 11 '17 at 04:56
  • You could be right. Modern AM car radios are nothing like the old AM superhets. They don't even have vibrators for the high voltage needed by the vacuum tubes. (The latter vacuum tubes could work with 12 volts on the anode, so vibrators went away.) AM radio is troubled by various forms of interference, such as modern high efficiency luminaires. – richard1941 Sep 23 '17 at 20:15