Laser Creates Rain Clouds Out of Thin Air

Clip 1: http://www.msnbc.msn.com/id/37029327/ns/technology_and_science-innovation/t/l...

"Ultra-fast pulses from a powerful laser can create droplets of water out of thin air, according to a new study. With the right conditions and large enough droplets, the researchers say, the technique could be used to make rain on demand.

Rain forms when water condenses around tiny particles in the atmosphere. Most of the time, dust or pollen do the job, but humans have long attempted to speed the process by seeding clouds with chemicals like silver iodide. Those chemicals provide the so-called "condensation nuclei" that trigger the consolidation of water into raindrops.

Unfortunately, such methods are difficult and could have environmental side effects, said Jérôme Kasparian, an optical physicist at the University of Geneva, Switzerland who was on the team that demonstrated the laser-triggered condensation. The study was published online May 2 [2010] in the journal Nature Photonics.

"The potential advantage of laser is that it can work continuously," Kasparian said. If lasers can trigger rain on a large scale, he said, it would also be more efficient and cheaper than spraying silver iodide out of airplanes or shooting it into the sky from rockets.

Researches have long known that short, strong laser pulses can ionize air molecules, creating pathways of ionized gas called plasma channels. Kasparian and his team wanted to find out whether those plasma channels could be of use to wannabe rainmakers.

"Our idea is to use the laser to ionize the air, and the ions that are produced can then serve as the condensation nuclei," Kasparian said.

To test the idea, the researchers first used an atmospheric cloud chamber, a box that enabled them to vary temperature and humidity. After saturating the air in the chamber, the team flipped on a several-terawatt laser (one terawatt is a trillion watts) and watched with surprise as visible water droplets formed. Three seconds after the laser pulsed, the droplets swelled to diameters of 80 micrometers, smaller than a raindrop but larger than expected. "

Clip 2: http://www.naiwmc.org/4dcgi/GetContentRecord/PB-893

Seeding Methods:
http://www.naiwmc.org/4dcgi/GetSubCategoryRecord/Cloud%20Seeding%20Technology...

NAWMC Main Site:
http://www.naiwmc.org

The Utah Division w/cute seeding animation:
http://water.utah.gov/cloudseeding