For five decades, most attempts at weather modification involved cloud seeding, a process usually meant to trigger rain by dispersing certain chemicals from airplanes. Thing is, it may not even work very well wile its environmental impact is cause for concern. Now, researchers from the University of Geneva are exploring whether firing lasers into the sky could stimulate rain more effectively and safely. They've published results from their experiments in the journal Nature Photonics. From Nature News:
Firing a laser beam made up of short pulses into the air ionizes nitrogen and oxygen molecules around the beam to create a plasma, resulting in a 'plasma channel' of ionized molecules. These ionized molecules could act as natural condensation nuclei, (optical physicist Jérôme) Kasparian explains.
To test whether this technique could induce droplets, the researchers fired a high-powered laser through an atmospheric cloud chamber in the lab containing saturated air. They illuminated the chamber using a second, standard low-power laser, enabling them to see and measure any droplets produced. Immediately after the laser was fired, drops measuring about 50 micrometres wide formed along the plasma channel. Over the next three seconds, the droplets grew in size to 80 micrometres as the smaller droplets coalesced.
The next step for Kasparian and his team was to take the technique outside....
Kasparian and his colleagues tested the (high-powered, portable) Teramobile laser over a number of different nights and in various humidity conditions. Once again, they detected the amount of condensation induced by monitoring how much the light from a second laser was back-scattered by any droplets. In low humidity conditions, the Teramobile laser did not induce droplets. But when the humidity was high, the team measured up to 20 times more back-scattering after the Teramobile laser was fired than before, says Kasparian, suggesting that condensation droplets were forming.