You can put your rain sticks away. Scientists have developed a way to summon water droplets out of thin air through the use of lasers. And while the droplets generated so far aren't quite raindrop caliber, the researchers' findings represent a large step towards us being able to control where and when rain falls.
Remember in 2009, when scientists from the Beijing Meteoroligical Bureau used 18 jets and 432 chemical explosives to induce cloud formation? The explosives were typically packed with dry ice or silver iodide, and worked by providing a surface for water vapor to at first condense, and then collect on (a process known as seeding) to give rise to clouds and, supposedly, rain fall.
Well according to Jérôme Kasparian, a physicist at the University of Geneva, the same thing can be done with lasers. Oh yeah, and without dispersing silver iodide throughout the atmosphere.
Kasparian is one of the authors of an article published in the latest issue of Nature Communications that describes the new laser method of controlling precipitation in outdoor environments.
The technique, which the researchers refer to as "laser-assisted water condensation," works by creating nitric acid particles in the air that can bind water molecules and prevent them from evaporating. These initial water particles form what is known as "condensation nuclei" on which more water droplets can attach and collect, eventually growing into tiny drops just a few thousandths of a millimeter in diameter. Their latest tests are based on findings originally published in Nature last year, wherein the team showed how their high-power, ultrashort laser could trigger the condensation of water droplets in a simulation chamber (pictured up top).
"We have not yet generated raindrops – they are too small and too light to fall as rain. To get rain, we will need particles a hundred times the size, so they are heavy enough to fall," Kasparian told The Guardian.
But their inability to produce raindrop-sized water droplets doesn't have the researchers discouraged. In fact, they think that in the future lasers like theirs could be used to trigger rainfall in sufficiently humid atmospheres, or even prevent rainfall from occurring by generating so many tiny droplets that none of them grow heavy enough to descend to earth. "Maybe one day this could be a way to attenuate the monsoon or reduce flooding in certain areas," Kasparian said.
You can also turn the laser on and off at will, which makes it easier to assess whether it has any effect. When the Chinese launch silver iodide into the sky, it is very hard to know whether it would have rained anyway.