[meteorite-list] Great Balls of Lightning
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Feb 10 12:45:52 2006
Great balls of lightning
10 February 2006
If you have ever seen a mysterious ball of lightning chasing a cow or
flying through your window during a thunderstorm, take comfort from the
fact that you have witnessed a very rare phenomenon. Indeed, ball
lightning - a slow-moving ball of light that is occasionally seen at
ground level during storms - has puzzled scientists for centuries. Now,
however, researchers in Israel have built a system that can create
lightning balls in the lab. The work may not only help us to understand
ball lightning but could even lead to practical applications that make
use of these artificial balls (Phys. Rev. Lett. 96 045002).
Ball lightning is thought to be a ball of plasma that is formed when a
bolt of lightning hits the ground and creates a molten "hot spot". The
ball can typically measure 30 centimetres across and can last for a few
seconds. Although they are generally created during thunderstorms, Eli
Jerby and Vladimir Dikhtyar from Tel Aviv University in Israel have now
been able to make lightning balls in the lab using a "microwave drill".
The device consists of the magnetron from a 600-watt domestic microwave
oven and concentrates its power into a volume of just one cubic
centimetre. The researchers inject the microwaves though a pointed rod
into a solid substrate made from glass, silicon, germanium, alumina or
other ceramics. The energy from the microwaves then produces a molten
hot spot in the substrate.
What the scientists then do is pull the microwave drill out of the
solid, which drags the molten hot spot and creates a hot drop. The drop
then becomes a floating fireball that measures about 3 centimetres
across and lasts for some tens of milliseconds (see figure). "The
fireball looks like a hot jellyfish, quivering and buoyant in the air,"
Although the composition of the laboratory fireballs still need to be
verified, they seem to contain components of the substrate material in
various phases, such as ions, neutral atoms and larger macroscopic
particles. This is similar to natural lightning balls, which are thought
to contain vaporized mineral grains from the soil that have been kicked
into the atmosphere by a lightning strike. Moreover, the lab-produced
fireballs appear to combine plasma and chemical oxidation and burning
processes. Again, this is similar to naturally produced balls in which
the vaporised sand grains are thought to react with oxygen in the air
and burn to release light.
"Our ability to generate such fireballs in a simple systematic manner
may lead to techniques for synthesizing fireballs from solid materials,"
explains Jerby. He even hopes that the lab-generated fireballs could be
used in practical applications such as coating, deposition, combustion
and energy production.
Received on Fri 10 Feb 2006 12:44:10 PM PST