Cloud Seeding in Australia
Cloud seeding is a typical weather modification process which helps
to change the amount of rain that pour out from the clouds. The purpose
is achieved by dispersing certain substances within the clouds to alter
the microphysical process within the cloud which increases precipitation
in the form of rain and snow.
Clouds were first seeded in Australia after WWII in NSW and experiments
were conducted in several other states soon. However, in the recent
years cloud seeding operations have been regularly undertaken by Hydro
Tasmania with considerable success.
How is Cloud Seeding Done?
The most widespread chemicals used in cloud seeding are dry ice (frozen
carbon dioxide) and silver iodide. Liquid Propane in its gaseous format
has also been used in some experiments to produce ice crystals within
the clouds. Using Propane has proved more advantageous than silver
iodide because it produces ice crystals at much warmer temperatures.
Cloud seeding is usually done by aircrafts equipped with dispersion
devices for spraying cloud seeding chemicals.
Seeding of clouds can only be done when they contain super cooled liquid
water - that is colder than zero degree Celsius. A substance with a
crystalline structure similar to ice like silver iodide helps the
freezing or nucleation. Substances like propane expansion or dry ice
cools the air to such a level that ice crystals can nucleate instantly
from the vapour phase but this does not happen with silver iodide.
Propane expansion or dry ice does not require any existing droplets in
the cloud because it produces high vapour super saturations close to the
seeding substance.
While in mid latitude clouds, the equilibrium vapour pressure is lower
over ice than over water. Thus, when ice particles take the form of
super cooled clouds, the ice particles grow at the expense of liquid
droplets. So if there is sufficient growth, the particles become heavy
enough to fall as snow from clouds that would produce no rain.
How Cloud Seeding can be made successful in Australia
In Australia, cloud seeding can be made successful by:
- Modern atmospheric research
- Negative Green faiths will have to be prevented from obstructing
progress blindly
- The most modern technologies in the fields of satellite remote
sensing needs to be applied,
- We should be prepared to utilize ‘know how’ from countries where
cloud seeding has been a great success and operational teams are
present. For example, countries like USA and Israel.
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