Firing lasers into the clouds may be a new way to modify them, but its practical application is currently limited.
European researchers produced an artificial ice cloud by using high-power, ultrashort laser pulses, Professor Thomas Leisner of the Karlsruhe Institute of Technology and the University of Heidelberg in Germany said.
The research focused on cirrus clouds, which are high, wispy clouds comprised of ice crystals and found in the upper troposphere. The troposphere, or lowest part of the atmosphere, is where our weather occurs.
A cloud simulation chamber was used to create conditions for cirrus clouds. The laser pulses enhanced the ice formation by a factor of 100, according to an abstract of the study published in the Proceedings of the National Academy of Sciences in June.
"The effect we discovered does not work on rain clouds, which are mixed phase containing water and ice," Leisner said. "So while it may be conceivable that the artificial ice clouds might be employed at some time in the future to shield the ground from too much solar radiation, there is no direct effect on precipitation."
In principle, such a laser could be deployed from a research aircraft soon, Leisner said. At the current rate of laser development, ground operation is conceivable within several years.
Humans have tried to modify the weather for at least 70 years. The most common approach is cloud seeding, which can be done by airplane or from the ground.
Benefits of rain enhancement and/or hail suppression are rather large, Project Meteorologist Jonathan Jennings of the West Texas Modification Association said.
A. Wayne Wyatt and Ken Carver of the High Plains Underground Water Conservation District reported in 1997 that 1 additional inch of rainfall over their district would bring a $280 million dollar regional economic impact. They also found that 1 additional inch of rainfall could increase crop yield from $10 to $35 per acre, Jennings said.
"Benefits include aquifer recharge, increases in river, lake and reservoir levels, decreasing irrigation and groundwater consumption, decrease in hail damage, increased agricultural production as well as fire suppression," Jennings said. Current studies show that rain enhancement could increase aquifer recharge up to 500,000 acre-feet per year across the San Angelo, Texas, area, he said.
Laser-modified clouds may be used to supplement cloud seeding in the future.
"One might think of using the laser-generated ice to seed liquid phase clouds below; however, It is not clear, at the moment, how effective such a scheme would be. Using current technology, it would not be economical anyway," Leisner said.
The research, performed by scientists at Karlsruhe Institute of Technology, the University of Heidelberg, the University of Geneva and the Free University of Berlin, will be discussed during the second Conference on Laser, Weather and Climate, Sept. 16 to 18 at the World Meteorological Organization in Geneva.