WMOD00279

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

Hail research

Hailstorms and their modificalion
are complex subjects because of
the great number of factors
influencing the formation of hail.
The objective of the Atmospheric
Sciences Department's hail
research is to determine through
physical experiments if the hail fOf.
mation process can be changed
through cloud seeding. No con-
clusive evidence yet exists that
cloud seeding affects hail fallen
to the ground. Alberta statistics
have demonstrated. however, that
ice crystal formation in the clouds
increases significantly after seeding.
To determine the impact of
seeding activities, it is necessary
to research the life cycle 01 a
hailstone. from 'birth' in the leeder
clouds, through the entire hail for.
mation process, to the lime it falls to
the ground.
A technological milestone to
understanding these events was the
development of a special aircraft
equipped to gather cloud physics
data inside a cloud. Developed joint-
ly with INTERA Technologies LId.,
the plane contains the latesl air-
borne measuring and data recording
equipment including computers for
data storage and analysis. The air.
craft !hes through the cloud,
measuring temperature, dew point,
liquid water content, cloud and ice
particle numbers and sizes, and air
motion.

When a cloud turret (storm feeder
cell) likely to produce hail appears,
the aircraft flies through it to detect
the presence of natural ice crystals.
Ideal candidates for seeding have
few ice crystals and plenty of water.
If the cloud is suitable, a plane fly-
ing behind the research aircraft
seeds it. After seeding, the research
aircraft !hes repeatedly through the
turret, documenting ice crystal con-
centration and growth. When tur-
bulence or ice on the aircraft wings
becomes severe, both aircraft move
to the next suitable cloud.
Belore the aircraft leave the
turret, ice crystals are producing
echoes on weather radar screens at
the Red Deer Airport. Ice crystals
identified by aircraft measurements
are then followed by radar into the
main storm. A brief overlap period
ensures aircraft and radar measure-
ments are following the same
package of ice crystals.
Researchers are now trying to
compare the characteristics of
hailstones that fall to the ground
with the characteristics of hail last
measured by the aircraft inside the
storm. A positive link will establish
the chain of events from formation
of original ice crystal to hailstone on
the ground. At this point, research
will be able to answer the question
of whether cloud seeding can sup.
press hail growth.

Computer-generated images of ice particles recorded inside a cloud; the
rounded shapes represent warer droplets.

Three computers on board the
research aircraft process data
from the laser probes and other
instruments.

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