WMOD00279

• Title: Atmospheric Sciences - Alberta Research Council
• Weather Modification - Doc Type: General Information

Cloud formation

Ratio 01 1974-78 loss 10 Risk
to 1938 -83 Average

Clouds are collections of water
droplets formed when moist air
rises. If the moisture conlent 01 the
air is great enough and the air rises
high enough, the relative humidity
increases to 100 percent. Waler
vapor condenses on tiny particles 01
dust and smoke to form the droplets
which make up the cloud.
Not all clouds produce precipita-
tion. Precipitation depends on
numerous factors in a complex
chain of events thaI researchers are
trying 10 identify and understand.
Much of Alberta's precipitation dur-
ing the summer falls from large
cumulus clouds and thunderstorms.
The basic hypothesis of the
weather modification experiments in
the hail and rain projects is that
cloud seeding can have the

.Sekl",Aver'ge
. Ne..Avtlr.ge
.AOOvtlA~er.ge

The haif loss paNerns. as illustrated.
show an even greater variability than
fain from one five-year period to
another. The effectiveness of cloud
seeding is not clear from these
patterns.

desirable effect of modifying hail
and rain processes occurring inside
clouds.
Some clouds that would not rain
naturally may be made to rain by
cloud seeding which. if done with
enough clouds, could increase total
precipitation. This, in turn, would
produce great economic benefits
particularly in southern Alberta,
which is prone to drought.
In the case of hailstones the idea
is to increase the number of
hailstones at small sizes rather than
allow fewer hailstones 10 grow to
potentially destructive sizes. Since
clouds contain limited amounts of
water, introducing artificial nuclei
means water must be shared by a
greater number of hail embryos,
thus retarding the growth of each.