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Name: Bruce
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
Dear Ask a Scientist,

I received a very interesting question from an associate who lived in the southwestern US for a number of year and it goes something like this:

When I lived in the Arizona many of the lightening storms would have lots of what I would call branch lightening (cloud to cloud many forks). While living in the eastern US, I rarely would see this phenomena except for this year. For some unknown reason, this type of branch lightening has been very pronounced to me here in the east this year. I did not know how to answer this question, but was wondering if it has something to do with the types of particulates that may or may not be present in the air or some type of ionization that is causing this to be more prevalent this year. Could you please advise me as to the answer, if any so that I can share this with my associate. Thank you in advance for all your information.


Replies:
Bruce,

Because there is usually little water vapor in the lower part of the atmosphere in the southwest, the air is less conductive and fewer cloud-to-ground strikes occur than in more humid areas like the eastern US. This also means that higher lightning energies (current) are required to be able to have a cloud-to-ground stroke in the southwest. Therefore, cloud-to-cloud lightning strokes and the branching between different cells in the thunderstorm (as you describe) are the preferential way for the cloud cells to dissipate their stored up static charge. If it has been drier than normal where you friend lives (for instance the southeast this year), he may have seen more cloud-to-cloud strokes than cloud-to-ground strokes.

David Cook
Lightning researcher at Argonne National Laboratory





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