Ask A Scientist© Weather Archive

> >>  name       Bruce
> >>  status     educator
> >>  age        30s
>
> >>  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.
>
>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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