Does lightning originate in the sky and just go down ( or
is there an opposite charge that goes up?)
Lightning is a fascinating phenomonon, one not totally understood by
scientists. What HAPPENS during the initiation of a lightning stroke is
fairly well recognized, and, thanks to high speed cameras, has even been
caught on film several times. Lightning is responsible for more deaths each
year (approx 200 in the U.S. annually) than either tornadoes or hurricanes.
Many people are not aware of the hazard that lightning presents when they
are outdoors in a thunderstorm.
You are correct in your presumption that there strokes that originate from
the ground in the direction of the cloud, as well as strokes that originate
within the clouds.
What is not totally understood is how the charge separates within the cloud,
that leads to the electric field differential that triggers the formation of
the conductivity channels within the atmosphere.
Here are some excellent websites that explain how lightning forms. Some are
pretty basic, and a couple are more advanced. You might check these out.
Wendell Bechtold, Meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO
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Update: June 2012