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Name: Adarsh
Status: student
Grade: 9-12
Location: Alabama
Country: USA
Date: Winter 2012-2013
Question:
What is responsible for the branch-like shapes of lightning. Why are there many nodes and forks in the path the lightning takes, instead of a straight line that is perpendicular to the highest point available for the lightning to ground itself?

Replies:
Adarsh

Lightning striking the earth is like a charged particle in an electric field. Instead of instantaneously proceeding from the Anode to the Cathode, the positron has to travel the space in between the two electrodes. The space between the clouds and the surface is not a homogeneous field, but probably has incremental variances in voltage from one point to another such that the current that creates the path is attracted to the next closest point that is an increment of lower voltage. So although I have not researched this specific problem, this explanation makes the most sense. Forks are probably created by the attraction of two points at the same voltage and distance attracting the current stream from the previous point. Kind of like packets in a modern computer communications network.

I find your question amusing when paraphrased to ?Why is lightning crooked??

Keep asking good questions. Sincere regards, Mike Stewart

Hi Adarsh,

Thanks for the question. Lightning is electrons moving and the electrons follow the path of least resistance. The path of least resistance is not always perpendicular to the ground. Furthermore, the branching serves to provide additional paths for the electrons and thus decreases the overall resistance. If you have taken physics, I can answer the question in more familiar terms of resistors. Please let me know.

I hope this helps. Please let me know if you have any additional questions.

Thanks Jeff Grell

Your question has no "simple" answer, because it addresses the whole issue of the mechanism(s) of the lightning discharge. I recommend the book "The Lightning Discharge" by Martin A. Uman, published by Dover Publications. (2001). This book gives a good analysis of the very complicated process of lightning discharges.

Vince Calder

The mechanism(s) of lightning discharges are very complicated, as high speed time lapse photographs of the discharges illustrate. There are changes in electric field, temperature and wind profiles as well. In fact, there is not universal agreement on ?how? lightning works, and part of that difference in opinion includes the mechanism for branching. A book ?The Lightning Discharge? by Martin A. Uman is thorough but not very readable, which reflects the complexity of the phenomenon. The web site:

http://www.ec.gc.ca/foudre-lightning/default.asp?lang=En&n=9353715C-1

has a lot of pretty photos.

Vince Calder

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