Swiss breakthrough could mean rain on demand
By Paul Ridden
May 4, 2010
Swiss researchers have reported laser-powered cloud seeding success, both inside and outside the laboratory. Inside the lab, the powerful infrared laser caused visible clouds of vapor to follow in its wake when fired into a water-saturated chamber and sensitive weather apparatus recorded spikes in water droplet density when it was fired into the skies of Berlin, although nothing was visible to the naked eye.
Experiments in cloud seeding have been going on for some time and varying degrees of success have been reported by showering silver iodide crystals or frozen carbon dioxide or even salt above clouds. A research team from the University of Geneva has achieved encouraging results from taking a more hi-tech approach.
The team fired short 220-millijoule pulses of infrared light from a laser into an illuminated chamber of water-saturated air at minus 24°C and noted the formation of clouds in the laser's wake. Team member Jérôme Kasparian explained the phenomenon by saying that the pulses stripped electrons from atoms in the air, encouraging the formation of hydroxyl radicals and converting sulphur and nitrogen dioxides into particles that act as the seeds on which water droplets grow.
Post-burst chamber examination showed that the concentration of water droplets along the plasma channel immediately after the laser was fired measured about 50 micrometers wide. After a few seconds the droplets grew to 80 micrometers as the smaller droplets fused together, doubling the volume of condensed water.
Real world application of the lab research has its detractors, Daniel Rosenfeld of the Hebrew University of Jerusalem is quoted in the New Scientist as saying: "Whatever has been documented in this experiment is of little relevance to natural clouds" and Thomas Leisner of Germany's Karlsruhe Institute of Technology said in Nature that he is "sceptical that this could be used to trigger rain on demand."
But Kasparian claims that the team has enjoyed similar success when pulses were sent 60 meters up into the skies over Berlin. Although there was no change visible to the naked eye, weather sensors confirmed an increase in size and density of droplets in the atmosphere.
It's early days for the research and the team is currently looking to boost the effect so that actual rain might result, no doubt hoping that success will not see them being taken away by the authorities as Donald Sutherland was in the Kate Bush video for 1985's Cloudbusting.
Via: New Scientist.