Stepped LeaderLecture #29
Lightning
Friday, 7 April 2001
Text Reading for Lecture
#29
Pages 396-402
Read this PRIMER on lightning
Powerpoint of complete lightning presentation
is located HERE
Stepped Leader
Upward-Moving Charge
Return Stroke
INCREDIBLE movie of a
commercial aircraft being
struck by lightning
Lightning facts (from Lyons, 1997)
1. The optical output of lightning is the equivalent of
about 100 million household light bulbs.
2. Lightning appears to flicker because of the multiple
discharges of energy that flow through the same
channel. They are separated by tens of milliseconds,
and in some cases, a stroke contains up to 50
separate flashes.
3. The downward-moving stepped leader travels at
an average speed of 200,000 mph, and the return stroke
averages 60,000 mph.
4. The amount of electrical current in lightning strokes
is highly variable, but usually averages several thousand
to more than 10,000 amps. The electrical potential
(voltage) can exceed 200 million volts.
5. The core of a lightning channel can reach temperatures
of 50,000 degrees Fahrenheit, which is about 6 times hotter
than the surface of the sun.
6. It is estimated that 100 flashes occur per second around
the globe.
7. The chances of being struck by lightning in the US are
between 1 in 250,000 and 1 in 400,000 (higher for golfers,
storm chasers!).
8. Lightning emits soft x-rays as well as visible light.
9. Lightning typically occurs within precipitation, but can
emanate from the anvil of a storm several miles from
precip.
10. So-called "heat lightning" is simply lightning that is
too
far away for thunder to be heard, and for which the light
reflects off the distant horizon owing to dust and other
particles.
11. So-called "ball lightning" is a spherical discharge that
can travel in erratic patterns. Some still debate its existence.
12. Some 25 to 30 million cloud-to-ground strikes occur in
the US each year.
13. The actual lightning channel is about the width of a
pencil.
14. Keranuophobia is the irrational fear of lightning.
The National Lightning Detection Network (NLDN)