Laser Conjures Clouds Over Berlin

By firing a laser into the sky over Berlin, scientists have successfully created clouds from thin air. It could be the first step towards a radical new way to modify weather.

A team of physicists have used a laser to conjure clouds from thin air. The technique has generated clouds both in the lab and in the skies over Germany and researchers think laser stimulation could one day be used to create on-demand rainfall.

Until now, creating rain relied on "cloud seeding," the scattering of particles of silver iodide into the atmosphere. However, cloud seeding hasn't proven efficient and no one knows how hazardous it is to spread silver iodide through the atmosphere.

The team, led by Jérôme Kasparian at the University of Geneva, thought lasers might be a more efficient, environmentally-friendly way to generate rain. They fired their laser into a chamber of saturated air. The laser pulses stripped oxygen and nitrogen atoms of their electrons, creating a plasma of ionized molecules.

These molecules acted as seeds for water droplets to grow around, creating long, thin clouds like airplane contrails along the laser's path, illuminated by the laser's green light.

Analysis of air in the chamber showed the laser had increased the total volume of condensed water droplets by half. But this test was on saturated air in lab conditions - nothing like Earth's atmosphere. So the team decided to do what any good scientist would do - take the laser outside and fire it into the skies over Berlin, Germany.

They didn't see the long, wispy clouds they'd hoped for form around the beam. But weather instruments confirmed a spike in the density and size of the water droplets when the laser was fired. The experiment was a success - the laser conjured clouds in natural conditions from unsaturated air.

The team's next step is to try to produce droplets big enough to fall as rain. Some scientists think it's overly optimistic to use a laser as a rainmaker, and so far it only generates clouds along its narrow beam. But if it can be made to sweep across the sky and to create a wider swath of precipitation, a new era in weather modification may be upon us.

Image: Jean-Pierre Wolf/University of Geneva