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Name: Jeff
Status: educator
Age: 40s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
Why when lightening strikes a tall pine tree it creates a clockwise spiral around the outside of the tree. I think the the electrical circuit between the cloud and the ground interacts with the earths magnetic field causing the charge ions to spiral and this charge going up and down the bark causing the disruption I see on the bark.


Replies:
Jeff,

The earth's magnetic field is much too weak to affect lightning. More likely, the pine tree has a natural twist in the grain. This could cause the lightning to follow the twist as it follows the lowest resistance path of sap to the ground.

David Cook
lightning researcher
Argonne National Laboratory


Dear Jeff-

That is an intriging theory about the spiral track of lightning. I'm not aware of any investigations into this area. Studies have shown that lightning follows the path of least electrical resistance through the air, and that magnetic field effects on ionized particles exist at much higher altitudes than the region of convective weather occurrences.

Here are a couple of links that discuss lightning formation and its effects in more detail This first one is a NASA link, and has some good graphics.

http://thunder.msfc.nasa.gov/primer/

This next one, from the publication "American Scientist," is more technical, but describes how the electrical charge in clouds originates.

http://www.sigmaxi.org/amsci/articles/98articles/blackintro.html

Wendell Bechtold, Meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO


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