Scientists analyze potential of using lasers to make rain

Jul 16, 2012 by Lisa Zyga feature
A high-powered laser pulse 10-cm in diameter generates multiple filaments, which is necessary for laser-induced condensation. Laser filaments can be generated at kilometer-range distances. Image credit: J. Kasparian, et al. ©2012 IOP Publishing Ltd

(Phys.org) -- Although pointing high-energy lasers at the sky to cause pouring rain is currently a high-tech dream, the motivation behind controlling the weather has existed since the days of our ancient ancestors. Throughout human history, many civilizations developed magical or religious methods in an attempt to increase or decrease precipitation. In light of this history, current techniques that shoot laser beams or launch chemicals into the sky for the same purpose seem to be just the latest manifestation of this goal.

Nevertheless, these cloud seeding techniques are controversial, both for their effectiveness at inducing and for their possible . In a recent review paper published in the IOP’s Journal of Physics D: Applied Physics, a team of scientists from Switzerland and Germany has examined the latest results of laser-induced condensation and discussed the future of the field.

One of the first successful demonstrations of laser-induced condensation (http://www.nature.com/ncomms/journal/v2/n8/full/ncomms1462.html) came just last year, when researchers – including the authors of the current review – used a powerful laser to produce tiny water in moderately humid air. The water particles were just a few micrometers in diameter, which is about 100 times too small to fall as rain droplets. However, the experiments demonstrated the ability to transform particles in a gas phase to a liquid phase through condensation, and larger droplets are expected to be feasible.

“At this stage, our work clearly shows that lasers can induce the formation of tiny particles,” Jérôme Kasparian of the University of Geneva in Switzerland told Phys.org. “This is not, at least at this stage, efficient cloud seeding for making rain, but rather a newly opened direction for research in this direction.”

Laser-induced condensation in a cloud chamber, illuminated by a green auxiliary laser. The cloud’s deformation reveals the air turbulence due to energy deposited by laser filaments. Image credit: J. Kasparian, et al. ©2012 IOP Publishing Ltd

As the researchers explain in this review, laser-induced condensation owes its feasibility in part to the rapid improvement in laser power in recent years. Over the past decade, commercially available laser power has increased by two orders of magnitude, reaching the petawatt level today. Scientists expect laser powers on the exawatt scale in the foreseeable future. In last year’s demonstration, the researchers performed experiments using a 100-TW Draco laser and 5-TW mobile laser called Teramobile, which is the size of a 20-foot freight container.

In addition to more powerful lasers, improving the results will also require a better understanding of the underlying mechanism of laser-induced condensation. The technique involves photodissociation, in which photons break down atmospheric compounds in the atmosphere. This process produces ozone and nitrogen oxides, which lead to the formation of nitric acid particles that bind water molecules together to create water droplets. Understanding the details of how this process stimulates particle growth, as well as how atmospheric conditions affect the process, are the most challenging questions in this field, according to the scientists.

“Making rain would require first to have tiny water particles grow into droplets with a size sufficient to fall as raindrops,” Kasparian said. “This depends on the atmospheric conditions, in particular the relative humidity, that these particles will encounter. For example, if the air mass in which the particles have been produced lifts along a mountain hill, it will cool down and condensation will be favored.

“Making rain would also require the production of an adequate number density of particles. If there are too few particles, we would only get a few drops at most. On the other hand, if there are too many particles, they will compete with each other to grab the water molecules available in the atmosphere. Ultimately, none of them will grow sufficiently to make raindrops, which may even reduce .

“Finally, the technique would also need to activate a large volume of the atmosphere, i.e., to sweep the laser sufficiently fast.”

Despite these challenges, the scientists also noted that using lasers to induce rain has its advantages, particularly its minimal side effects compared to other techniques. For example, methods that involve injecting silver iodide particles into clouds run the risk of having unintended consequences for the surrounding atmosphere, a problem that lasers avoid. Laser-assisted methods also offer better control than methods, since the lasers can be turned on and off and precisely positioned. This control also makes it easier to determine how effective the technique is, since critics often question whether rain might have occurred even without intervention.

In the future, the researchers recommend investigating the ability of lasers to seed clouds on a larger scale. Such a task will require further experimental data as well as theoretical modeling.

“Our aim now is to tackle the questions that remain open, especially to determine the optimal laser conditions to maximize the condensation process, and to assess for the possibility to obtain macroscopic quantities of condensed water,” Kasparian said. “This also requires an understanding of the physical mechanisms at the root of laser-induced condensation, with the ultimate goal of being able to model the process quantitatively.

“Besides the technical feasibility, as discussed above, further experiments will allow us to assess whether laser rainmaking could be cost-effective. This can easily be expressed in terms of the cost per unit rainwater volume obtained. This will depend very much on the ultimate laser power required to get a significant amount of water, which we need to further investigate.”

Explore further: First dark matter search results from Chinese underground lab hosting PandaX-I experiment

More information: J. Kasparian, et al. “Laser-assisted water condensation in the atmosphere: a step towards modulating precipitation?” J. Phys. D: Appl. Phys. 45 (2012) 293001 (13pp). DOI:10.1088/0022-3727/45/29/293001 http://iopscience.iop.org/0022-3727/45/29/293001

Journal reference: Journal of Physics D: Applied Physics search and more info website

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SatanLover
2 / 5 (4) Jul 16, 2012
They are already use many techniques for inducing rain like cloud seeding missiles. so what is so controversial about this? This technique is a lot less polluting than missiles which contain many chemicals and destroy soil pH.
sirchick
3 / 5 (4) Jul 16, 2012
I don't like the idea of inducing rain we barely understand the weather system as it is why mess with it. I recall reading celebrities want to pay to prevent rain ruining their shows, I think one was Elton John.... its ridiculous.
foofighter
2.3 / 5 (3) Jul 16, 2012
Baal was just as effective at bringing rain as was Yahweh.
TS1
1 / 5 (1) Jul 16, 2012
Well there are these "giant ionizers, shaped like giant lampshades" used by the Swiss company Meteo Systems International (meteo-systems.com).

According to some articles (e.g. http://eideard.co...-dhabi/) their system was able to generate dozens of man-made rainstorms in Abu Dhabi about 2 years ago.
elektron
5 / 5 (1) Jul 16, 2012
Forecast is for light rain.
antonima
Jul 16, 2012
This comment has been removed by a moderator.
heatseek
2 / 5 (3) Jul 16, 2012
I wonder how the technique will fair in a match with Hopi Rain dancers?
Mr_Frontier
1 / 5 (2) Jul 16, 2012
We need to start accepting that our species will always be one of manipulation and control. It's what we were meant to do. Our vision is tame this solar system, this galaxy, this universe. We will be brutal at first, and I only hope we can soften with wisdom.
B Bau
1 / 5 (2) Jul 17, 2012
While I'm not keen on the idea of using something like that hear, this may become a path to helping to terraform other planets given the right chemical makeup.
Satene
not rated yet Jul 17, 2012
here are these "giant ionizers, shaped like giant lampshades"
The excessive nucleation may bring more droughts than rains by itself. If the nuclei are too numerous, then the water condenses in form of tiny droplets, which aren't able to precipitate and which form the smog instead. This is the mechanism of aerosol pollution induced droughts over China and another areas. In addition, the thin fog is transparent for infrared radiation and it serves as a heat absorber instead of reflector, so it contributes to warming, because the water vapour is significant greenhouse gas. Therefore for successful generation of rain the nucleation must be followed with some droplet coalescence, for example with using of electric field. As far I remember, the lasers were already tested for it, but without greater success...
Eoprime
not rated yet Jul 18, 2012
hm, If it works out it should be possible to write something in the sky :)

Cloudpainting!
antialias_physorg
not rated yet Jul 18, 2012
If it works out it should be possible to write something in the sky

Like: "Get an umbrella. Now!" ?

The novel 'O-zone', by Paul Theroux* had an interesting idea for creating rain: Paving tracts of land with asphalt to create updrafts from the heated air. This would create a 'virtual mountain' where the uprushing, moist air would mix with the colder air further up and make it rain.

From a phyiscs standpoiont that should actually work (if you know the predominant wind direction in an area you could 'target' the rain pretty well, too). But it probably would be a nasty eyesore in the scenery( probably would look like a giant parking lot).

*Don't bother reading the book, it's actually a pretty boring.