Rain-making lasers could trigger showers on demand
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By Zeeya Merali
The rain dance is getting a twenty-first-century revamp using laser technology. Optical physicists have demonstrated that shooting lasers into the air can trigger the formation of water droplets, a technique that could one day help to stimulate rainfall.
For more than 50 years, efforts to try to artificially induce rain have concentrated on 'cloud seeding' -- scattering small particles of silver iodide into the air to act as 'condensation nuclei', or centres around which rain droplets can grow. "The problem is, it's still not clear that cloud seeding works efficiently," says optical physicist Jérôme Kasparian at the University of Geneva, Switzerland. "There are also worries about how safe adding silver iodide particles into the air is for the environment."
Kasparian and his colleagues realized that there might be a more environmentally friendly alternative. 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, 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 (see video). 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 team's results are published online in Nature Photonics.
Rainmaker
The next step for Kasparian and his team was to take the technique outside. The researchers already have experience using plasma channels to modify the weather: in 2008, they demonstrated that a beam from their high-powered portable 'Teramobile laser' could be fired into thunder clouds, triggering an electric discharge. The beam was able to reach its target without being deflected because the generated plasma channel modifies the speed at which light travels through air -- slowing it down in the centre of the beam and speeding it up at the sides. This causes the beam to continually self-focus, helping it to maintain a high intensity across large distances (see 'Bendy laser beam fired through the air').
This time, Kasparian and his colleagues tested the 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.
Roland Sauerbrey, an expert on laser physics at the FZD Dresden-Rossendorf Research Centre in Dresden, Germany, says that the team has the potential to create a "breakthrough technology". "This is the first time that a laser has been used to cause condensation outdoors," he says.
However, the technique is still in its early stages. "We can only create condensation along the laser channel, so we won't be going out and making rain tomorrow," Kasparian notes. He and his team are now investigating whether they can create condensation over a wider area, by sweeping their laser across the sky.
Thomas Leisner, an atmospheric physicist at the Karlsruhe Institute of Technology, Germany, remains cautious about the feasibility of scaling up the technique in this way. "I am sceptical that this could be used to trigger rain on demand," he says. But he adds that the technology will have other uses. The researchers should now calibrate the relationship between the amount of condensation produced by the laser and the prevailing atmospheric conditions, he says. "They could use the amount of condensation produced by their laser as a measure of water saturation to help forecast the chance of rain," he says.
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13 Comments
Add CommentI was going to ask what happens when a lightning bolt follows one of these plasma channels from the cloud back to the laser. But it seems this was one of the original purposes of the Teramobile, and it failed to induce enough ionization to trigger lightning in any field experiment. I guess the research team wasn't willing to give up on weather modification?
Reply | Report Abuse | Link to thiswill this work to disapte oil??
Reply | Report Abuse | Link to thisDissapate oil? I wonder how many conservatives along the gulf coast are still shouting "Drill baby, Drill!"
Reply | Report Abuse | Link to thisanybody hear from Sarah?
Reply | Report Abuse | Link to thisCan't we just drop the incessant political BS and talk about the subject of the article?
Reply | Report Abuse | Link to thisCandide: I agree with you.
Reply | Report Abuse | Link to thisUnfortunately, a lot of people are political and opine in this type of forum is because they are in desparate need of belonging. In fact, the majority of the population is poised to take a side and go with it despite the actual issues.
If one pays close attention, everytime some lunatic acts out, what is one of the first questions asked? Right, where do they stand politically. This is because people (one side or the other) love to see the other side take a hit. And if the other side is wrong, they are right.
What this boils down to is the human ego grasping at anything to make itself feel important and accepted. Thats all. So, when someone makes a politcal comment in a scientific article, they are simply saying, "hey look at me. I belong to a group and I need to make my point so I feel like a somebody".
Do these people truly care about the issues, or just being right.
I know that was a lengthly rant, but I just get tired of politics.
Talking politics is fine, in the right place and context. If the subject of this article was politics related then it would be appropriate.
Reply | Report Abuse | Link to thisThe subject is about the science of using lasers to try to make rain, which IMO could be a very interesting subject.
It seems to me that if this CAN be used down the road to induce cloud formation, and hence rain, it would have to be used very sparingly. After all, if you're using this to create rain west of the Rockies, aren't you taking moisture out of the air that might have provided rain over the Great Plains? (Correct me if I'm wrong.)
Reply | Report Abuse | Link to thisI foresee great political battles over rain rights.
That thought (rain rights) also crossed my mind.
Reply | Report Abuse | Link to thisLike most anything this could be used for good purposes or not.
However right now it seems to be a long ways from being able to actually make it rain.
It seems, to me, it would take one hell of a laser to create a significant storm, so I don't think it would be appropriate to break out the investment dollars, anytime in the near future; probably about the same time fusion becomes popular as a significant source of energy.
Reply | Report Abuse | Link to thisBy the time they get this cranked up to make rain I could get through law school and be ready for 'em....
Reply | Report Abuse | Link to thisThen while I'm waiting I could make it through med school too....
By the time they get this cranked up to make rain I could make it through law school and be ready for 'em....
Reply | Report Abuse | Link to thisThen while I'm waiting I could go through med school....
Why not instead of complaining about something that's years away at best,and coming up with something that's constructive. Like why don't we take some of our nuke powered ships out of mothballs or retire some,and use them to tug some of these big pieces of ice that are breaking off,to places around the world that need the water instead of just letting it melt.What a gesture of peace that would be using,an ex war machine for a humane purpose.
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