There are those who plant vegetables. A familiar saying says: "who sows winds and reaps storms." And what about sowing clouds? Cloud seeding is a popular technique in places like Idaho or Colorado. They are places where drought and the growing demand for water demand creative solutions. But the sowing of clouds also promotes the appearance of snow.
Directed by the atmospheric scientist at the University of Colorado Boulder, Katja Friedrich, and her colleagues, the investigation began on a cold day in January 2017. Radar and other tools were used. For the first time, the volume of snow produced through cloud seeding was accurately measured. The team observed how the precipitation affected a land in western Idaho.
The gentle snowfall was not natural. It had been unleashed through cloud seeding. A technique in which small particles are mixed in the atmosphere to try to generate more precipitation than would normally fall. The system is notoriously difficult to measure.
Earlier this year in the Idaho Payette Basin, the team monitored three cloud seeding attempts from start to finish. The collaborators published the results in PNAS.
From inside the cloud
«We traced the planting plume from the moment we put it in the cloud. We followed him until he generated snow that really fell to the ground, ”Friedrich explains. In total, that cloud seeding event and two later that month produced an impressive total. Almost 282 Olympic-size pools worth of water.
Friedrich adds that research is an important first step to better understand how efficient cloud planting can be in creating those winter wonders. "All the people you talk to will say, even if you can generate a little more snow, that helps us in the long run," he adds.
On January 19, that small amount of additional snow began with a plane flight. Just before sunset, a plane owned by Idaho Power Company used a series of flares. Injected particles of silver iodide into a formation of natural clouds that passed over.
The idea of cloud seeding is simple. Light water vapor is converted into heavy drops. If everything goes as planned, the drops of water will begin to freeze around the aerosols, forming snow.
But it is also difficult to have a clear idea of how effective that operation really is. Estimates range from zero to 50% of additional snow, says Friedrich it's a statement. That is why the group used a nearby radar antenna to observe the clouds while the water inside thickened. Until finally succumbed to gravity.
According to the team's calculations, the snow fell from those clouds for approximately 67 minutes. He sprayed 2,330 square kilometers of land in about a tenth of a millimeter of snow.
There was barely enough snow to hold on to the researchers' eyelashes. But it was the water that, had it not been for the sowing of clouds, would have remained in the air. "If we had not sown these clouds, they would not have produced any precipitation," says Friedrich.
"Now we can finally put a number on the amount of water we can produce through cloud seeding," he says.