Re: [Phys-L] lightning

["LaMontagne, Bob" <RLAMONT@providence.edu>]

Thanks John,

This so-called "dark lightning" that produces gamma rays is fascinating. By coincidence, one of my astronomy news feeds sent this out today:

http://www.universetoday.com/102917/navy-researchers-put-dark-lightning-to-the-sword/

Scroll down to a movie that NASA has produced explaining the process. It is well done and might be of classroom use.

Bob at PC
________________________________________
From: Phys-l [phys-l-bounces@phys-l.org] on behalf of John Denker [jsd@av8n.com]
Sent: Friday, June 14, 2013 1:44 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] lightning

In case anybody on this list hasn't been following the news super-
closely:

Thunderstorms are seriously energetic.  In addition to thunder and
visible lightning, they produce gamma rays.  This was discovered
within the last 25 years.

Not only that, they produce antimatter!  Sometimes huge numbers
of positrons come shooting out the top of the storm.  This was
discovered within the last two or three years.

============

Among other things, this overthrows the conventional wisdom that
there is no naturally-occurring antimatter anywhere around here.

===========

This also gives me another chance to tilt at one of my favorite
windmills:  Scientific methods.
  http://www.av8n.com/physics/scientific-methods.htm
The guys who discovered TGFs (terrestrial gamma flashes) weren't
looking for them.  They were not "testing the hypothesis" that
TGFs exist.  The spacecraft was intended to look for /cosmic/
gamma-ray sources.  Then they noticed, hey wait a minute, some
of the flashes are coming from the wrong direction.

It was not easy, but they managed to reprogram the instrument
while it was still on orbit, to get it to look down.


  http://www.google.com/search?q=lightning+gamma
  http://www.google.com/search?q=lightning+positrons
especially
  http://science.nasa.gov/science-news/science-at-nasa/2011/11jan_antimatter/





====================================================
On 06/14/2013 10:04 AM, Trivilino, Herman wrote:

> > I don't know for sure, but I suspect that free electrons don't last long.
> >  It's too easy for them to attach to molecules to form negative ions.

> Right.  As long as the flash of lightning?

That depends.  Lightning is not a single thing. There are multiple
different time-scales involved.  Many statements that are true for
the dark leader are not true for the return stroke, and vice versa.
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