Can you tell me about the technology know as cloud seeding?
Cloud seeding is accomplished by adding something to
saturated air (particularly non-precipitating clouds)
that will serve as effective condensation nuclei (producing
rain droplets) and/or will decrease the cloud temperature to
the point where it will produce precipitation.
Typically, particles such as ice crystals, dry ice (solid
carbon dioxide), silver iodide, and salt (sodium chloride)
are used as condensation nuclei.
The results of cloud seeding experiments are not encouraging,
as huge amounts of condensation nuclei are required to
produce very little precipitation. This is made even worse
by the fact that when precipitation is really needed, the
air is often quite dry and does not produce clouds of enough
extent to make seeding practical.
David R. Cook
Atmospheric Physics and Chemistry Section
Environmental Research Division
Argonne National Laboratory
Cloud seeding is an effort to produce or increase rainfall from clouds.
Condensation nucleii are added to clouds either from aircraft or from the
ground, to increase the number of raindrops that form in the clouds. The
effectiveness of different methods is not clear, and weather modification in
this manner has mixed results.
Here is a link that explains the different processes of raindrop formation
and how cloud seeding can assist or enhance these processes.
Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO
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Update: June 2012