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Lightning and Relative Motion
A Virtual Recollection-
This page deals with a phenomenon I ran across back in July of 1958 on a trip out West.

I was driving my pickup across Kansas in the late afternoon during a tornado watch and severe lightning  storm--some of the largest and longest lasting bolts I have ever seen.

As the bolts of lightning went from the clouds to ground--about 4 or 5 miles[1] from me, I heard a  crackling sound directly behind me.

I noticed that the faster I went, the louder the sound got, as I slowed, the weaker the sound--very  puzzling.

It turns out that it was a connector (PL-259) on the end of a short piece of coax leading to a long whip antenna mounted on the truck cab.   (cut for 10 meters, 28 MHz)  

I held the connector as I drove and watched: every time there was a lightning strike, there was corresponding arcing across the connector, looking exactly like a spark plug.

The more severe the lightning strike, the bigger the arc; the faster I drove, the brighter the arcing.

When I pulled over and stopped, there was no sign of arcing, regardless the severity of the lightning  strikes.

I have never read nor heard of such a phenomenon, and to this day I don't have a real explanation.  Please let me know if you have observed this, and/or if you have an explanation!   webmaster

  [1] Estimating accurate distances under those circumstances could be problematic, the real distance could conceivably be as close as ~1 to 2 miles, and farther than 5 miles.

Comments,  Questions, or Suggestions: webmaster

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Points to Ponder
1)_ Was this Positive or Negative lightning?

2)_ Could this phenomenon have been a simple case of Magnetic Induction? 
      (i.e., magnetic field, conductor, and relative motion)

3)_ The voltage had to be greater than ~2500 Volts (~1kV/1mm).
      (The gap between center pin and shield of the PL-259 approximately 3 mm.)
 

Positive lightning makes up less than 5% of all strikes. However, despite a significantly lower rate of occurrence, positive lightning is particularly dangerous for several reasons. Since it originates in the upper levels of a storm, the amount of air it must burn through to reach the ground usually much greater. Therefore, its electric field typically is much stronger than a negative strike. Its flash duration is longer, and its peak charge and potential can be ten times greater than a negative strike; as much as 300,000 amperes and one billion volts!
 


One Possible Explanation
 A = ~5,000 feet
 L = ~2 miles
  E = 1,000,000 kV
  I = 300,000 Amps
  V = 88 feet/sec 
      (60 MPH)
Assuming Positive lightning: Michael Faraday’s principle of Induction, expressed as an electric current being induced in a conductor in terms of the number of magnetic lines of force that are cut by the conductor and the relative motion between same.
Some questions yet to be answered:
 
 

  

 
 
 
Experimentation:
An apparatus for reproducing the phenomenon towards a better understanding.
A simple apparatus for reproducing relative motion during a lightning storm.

The motor is battery powered with a speed control, and is isolated.

In its present configuration it may suffer from common mode rejection: half of the antenna is moving toward while the other half is moving from...

A remedy may be to use an isolated counter weight in place of one of the antenna halves.

I have tried this apparatus only once: it was a mild storm with lightning strikes as close as 2 - 3 miles. Results was Zero Volts.

I am making the mod mentioned above and will try again.

The storms in south central Virginia are pretty tame compared to central Kansas.
 

     glen

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