From: Paul Doherty (pauld@exploratorium.edu)
Date: Sat Sep 25 1999 - 19:19:15 PDT
Message-Id: <l03110701b41331ef8ec5@[192.174.2.173]> Date: Sat, 25 Sep 1999 18:19:15 -0800 From: Paul Doherty <pauld@exploratorium.edu> Subject: Re: pinhole Re: Lightning strikes
Hi Sue
Indeed the step leader progresses from the cloud toward the ground in 50
meter long (on the average) jumps, separated by 50 microsecond rests. Once
in a while two step leaders split off leading to forks in the lightning
path. When one of the step leaders gets to within 50 meters of the ground a
step leader comes up from the ground to finish the connection between the
cloud and the ground. Then the - usually- negative charges which fill the
upper part of the step leader flow down to meet the positive charges in the
step leader that came up from the ground, they continue to flow into the
ground. Thus clouds bring negative charges from the atmosphere to the
earth. Images of this can be seen in books such as "the Lightning Book, by
Uman.
Paul D
>
>It is also my understanding that a "step leader" must form from the ground
>TOWARDS the cloud in order for the lightning to complete its path to the
>ground. I have seen photographs that show step leaders lifting off of various
>objects in a neighborhood. The "lucky" step leader (so to speak) is the one
>that manages to connect with a downward lightning strike from the ground.
>
>I think I saw this in a science video--any comments? Has anyone heard of this
>phenomenon?
>
>Sue "whereever you go, there you are" Hinojoza
>
Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld
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