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If so, then shouldn't lightning be reflected back into the sky everytime it hits the earth, due to an impedance change?

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closed as unclear what you're asking by PM 2Ring, Jon Custer, Thomas Fritsch, JMac, ja72 Aug 13 at 22:20

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    $\begingroup$ Are you referring to an electrical power transmission line? $\endgroup$ – Bob D Aug 13 at 16:00
  • $\begingroup$ I think you need to edit the question and frame the situation a bit. $\endgroup$ – ja72 Aug 13 at 16:25
  • $\begingroup$ @BobD Are there any others? $\endgroup$ – Goldname Aug 13 at 18:14
  • $\begingroup$ @ja72 situation is a lightning strike on earth. Not sure how I can frame it better. $\endgroup$ – Goldname Aug 13 at 18:15
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It would be reflected back (almost) completely if the earth was metal but it is not. In fact the earth and sea present a dissipative load to the current pulse and there is also a fair amount sideways radiation that propagates very well in the cavity resonator formed by the ionosphere and the earth. It can and does propagate all around the earth and these lightning strikes are the main cause of interference into long range LF radio communications limiting not only their practical range but also any achievable information rate.

Note too that the cloud to earth distance is quite short relative to the effective wavelength of lightning (a 1msec pulse would have an effective wavelength on the order of ~300km), so there is probably not much to be gained by looking at it as a vertical transmission line whose length is ~10km. That is not the case for the EM cavity whose diameter 40,000km.

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