From: Paul Doherty (pauld@exploratorium.edu)
Date: Thu Sep 23 1999 - 12:19:58 PDT
Message-Id: <l03110728b4102beac1ef@[192.174.2.173]> Date: Thu, 23 Sep 1999 11:19:58 -0800 From: Paul Doherty <pauld@exploratorium.edu> Subject: Re: pinhole lightening
Hi Gary
Actually no one knows precisely how clouds get charged.
Usually clouds are charged when: there is a part of the cloud which
contains ice crystals and a part that has water drops. There also has to be
a strong vertical air flow. (i.e. a recipe for cumulus clouds.)
This results in a basic separation of charge. The tops of the clouds are +
(90% of the time) and the base is - (It's more complicated than that).
(One of the parts that is little understood is why the falling water drops
tranmsporting negative charge downward through the cloud leave behind the
charge at the bottom of the cloud while they continue to fall to the
ground.)
The ground under the cloud is a conductor and has an induced charge
opposite that of the bottom of the cloud.
Most of the lightning is between the top and bottom of the cloud.
Only 10% or so is between the cloud and the ground.
Indeed there are forces between the charges in the cloud and electrically
charged water drops. But these forces are not great enough to move the
negative charge droplets slowly from the bottom of the cloud to the top,
instead the forces rip apart and ionize molecules in the air allowing
charges to move more rapidly to neutralize the charge separation.
Paul D
Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld
This archive was generated by hypermail 2b29 : Thu Oct 19 2000 - 11:09:33 PDT