Regarding making clouds with lasers in a lab: Three entries from my new book: Fixing the Sky: The checkered history of weather and climate control http://cup.columbia.edu/book/978-0-231-14412-4/fixing-the-sky
236 ³We are lords of every specimen of air which we can bottle up or imprison in our laboratories but in the open air we are practically powerless² -- Sir Napier Shaw ix. The possibility but not the desirability of weather and climate control entered my consciousness in the early 1970s when I was a graduate student in atmospheric science at Colorado State University and one of my air force colleagues proposed to zap clouds with laser beams to make them more energetic. I think he was wondering if a focused beam of radiation could destroy hailstones, perhaps like microwave medical treatment for kidney stones, although I suspect his patrons had other ideas. 111 In 1884 British physicist Oliver Lodge demonstrated that smoke and dust can be precipitated by the discharge of a static electric machine. He then asked, ³Why should not natural precipitation be assisted artificially?² In his largest scale experiment, he cleared a smoke-filled room and discovered that electrical charges encourage the coalescence of infinitesimally small cloud droplets into ³Scotch mist or fine rain.² He opined that clearing London fogs and abating industrial or urban smoke might be a ³difficult but perhaps not impossible task,² equivalent to such other noble quests as navigating the Arctic Ocean, exploring the Antarctic continent, scaling Mount Everest, and conquering tropical diseases. Lodge regarded the future prospects with hope and felt that the control of the atmosphere ³will be tackled either now or by posterity.² But applying this technique outdoors was another matter, and he admitted the propensity of physicists ³to rush in where meteorologists fear to tread!² James Fleming Professor of Science, Technology and Society Colby College 5881 Mayflower Hill Waterville, ME 04901 Email: [email protected] Phone: 207-859-5881 Fax: 207-859-5846 Web: http://www.colby.edu/profile/jfleming On 5/3/10 12:24 PM, "Dan Whaley" <[email protected]> wrote: > http://www.nature.com/news/2010/100502/full/news.2010.213.html > > Rain-making lasers could trigger showers on demand > > Lasers that stimulate condensation may help to induce rain > artificially. > > Zeeya Merali > Laser-assisted condensation / Make rain while the laser shines.J-P. > Wolf / University of Geneva > > 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 Photonics1. > 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 discharge2. 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. > > ADVERTISEMENT > > 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. > > * > References > 1. Rohwetter, P. et al. Nature Photonics advance online > publication doi:10.1038/nphoton.2010.115 (2010). > 2. Kasparian, J. et al. Opt. 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