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I recently heard an anecdote about cloud-to-ground lightning striking an area where some kids were playing 20 seconds prior. They experienced their hair rising which would indicate there is a significant voltage preceding such strikes.

I assume that a common multimeter would indicate a very high voltage between the ground and a cloud which is about to produce a ground strike (and it would facilitate the strike).

  • Would there be some voltage between the ground and, say, 2-3 meters in the air?
  • How long before the strike would this voltage become noticeable (significant relative to noise)?
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    $\begingroup$ this is detectable several kilometers before the lightening is coming,one can see the signal meter is rising and when the lightening is released the signal meter suddenly drops.this is for a ham radio but the same happens if you connect a multimeter to an antenna and ground(voltage rises and suddely drop when lightening strikes). $\endgroup$ – trond hansen Jun 26 '17 at 17:27
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There is always a background voltage difference from the ground up, of about 100V per vertical meter resulting in a net voltage difference of about 400,000V between the top of the atmosphere and earth ground. However, being a good insulator, makes for lousy conductivity, therefore the current density is extremely low which would make measuring with a common multimeter pretty hard: there's just not enough surface area on those tiny leads over which to contact air and ground. Add to that the very low current density, and your digital multimeter (DMM) is nowhere near sensitive enough to measure that voltage difference.

Although the moments preceding a lightning strike will generate a potential of tens of millions of volts, using a DMM still leaves you with a few big problems:

1) Lighting is an energy transmission that channels through a "pipe" of ionized air molecules. You'd be hard pressed to predict where that pipe is going to set up, getting there in time, and most importantly, surviving the instant supernova of steam that your body would turn into.

2) You're still left with the problem of the tiny surface area of DMMs leads. Sure, there's a big voltage potential, but the current density is still too small to measure with an unmodified DMM. Like Trond Hansen notes above, you'd need to connect your DMM to a large "collector" to actually see the difference, (then calculate the current density observed based on the surface area of your collector.)

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    $\begingroup$ just to be clear standing close to an antenna during a thunderstorm might not be in the top ten of the brightest idea one can have. $\endgroup$ – trond hansen Jul 4 '17 at 8:26
  • $\begingroup$ Are you positive (lol) about the background voltage? If I remember correctly, the top pf the atmosphere is ~100 km, or 100,000 meters. 100 volts/meter would be 10,000,000 volts $\endgroup$ – cliff Jun 1 '18 at 2:42

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