Seeds of doubt: Cloud seeding has been controversial, but a new 45-year study seems to show it can cause a modest improvement in rainfall.
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SYDNEY: A 45-year Australian trial is the best evidence yet that cloud seeding – the practice of artificially inducing clouds to make rain – really works.
Since the mid-20th century scientists have attempted to produce rain by dispersing chemical substances into the clouds and stimulating precipitation. However, until now, there has been little concrete scientific evidence that cloud seeding is effective.
“This is the first time that an independent analysis of cloud seeding data over several decades has shown a statistically significant increase in rainfall,” said Steven Siems, a meteorologist from Monash University in Melbourne and leader of the study.
Significant finding
The Monash team, in conjunction with renewable energy firm Hydro Tasmania, analysed monthly rainfall patterns over the hydroelectric catchment area between May and October from 1960 until 2005.
As they detailed in the Journal of Applied Meteorology and Climatology the analysis revealed higher levels of rain in the parts of the catchment where the rain making technique was used than in those where it was not.
"A number of independent statistical tests showed a consistent increase of at least five per cent in monthly rainfall over the catchment area," said Siems.
For the cloud seeding technique, the researchers select clouds using specialist weather radar technology that allows them to see all the tiny processes that take place within them.
Once clouds for seeding are chosen, minute particles of a silver compound are dusted into them by light aircraft to stimulate rain formation.
Super-cooled water
Anthony Morrison, a climatologist at Monash and co-author of the study, explained that these silver particles cause super-cooled water in the clouds to freeze. As these particular clouds are so high in the atmosphere that they are below freezing point, the frozen drops recruit water and get heavier causing them to fall from the clouds as rain.
However, the researchers caution that the result may be due to the unique clouds in this part of Tasmania and would be difficult to reproduce elsewhere.
“Clouds over the Southern Ocean are different to any other clouds”, Siems told Cosmos Online. “They are really loaded with super cool liquid water.” Just as important, he said, is the remoteness of the location: "the air in the Southern Ocean is exceptionally clean with virtually no pollution."
And the researchers are still at a loss to precisely explain how the technique was successful.
“They’re really not comparable to clouds that have been seeded anywhere else in the world," said Morrison. "Further field measurements of cloud microphysics over the region are needed to provide a physical basis for these statistical results.”
cloud seeding
however much i enjoy and understand this information we need more, as in how do you make the rain and what (if you were to show) would you use as an example? think about the little things when you prove your information. thank you
sincerely yours
jessica