Wringing Out the Clouds

The U.S. Weather Bureau has little faith in weather control. Last year the weathermen announced that they had tried seeding clouds with dry ice and found the trick does not work (TIME, Dec. 6). Last week the bureau's chief, Dr. Francis W. Reichelderfer, told a Manhattan meeting of the American Meteorological Society and the Institute of the Aeronautical Sciences that man-made weather is a very unreliable project. The dry ice method may work locally under special conditions, said Reichelderfer, but the physical forces in full-scale weather are too big to be affected by man.

This time Dr. Reichelderfer got an argument from an expert: Nobel Prizewinner Irving Langmuir of General Electric Co. The dry ice method does work, Langmuir insisted, if it is done right.

Project Cirrus (a joint cloud study program of the services and G.E.) has been very successful, said Dr. Langmuir. Thirty-five of its cloud-seeding flights changed super cooled clouds* into ice or snow crystals. Last October, at Albuquerque, two large cumulus clouds were sprinkled with dry ice. They turned into a furious thunderstorm that drenched Albuquerque with heavy rain at a time of year when rain is uncommon.

With low-hanging stratus (i.e., solid layer) clouds, Project Cirrus was just as successful. Langmuir told how the planes had drawn Greek letters and "racetrack" patterns in stratus clouds by dropping small amounts of dry ice (see cut). Sometimes the cloud was dissipated so completely that blue sky showed through the gaps. Langmuir believes that dry ice can be used to clear clouds from over airports.

One mistake of unskilled rainmakers, Langmuir explained, looking coldly at the Weather Bureau, is that they don't pick the right kind of cloud. Unless at least part of the cloud is below freezing, the dry ice will not work. Another mistake: using too much dry ice. A few pounds per mile are usually enough. If the plane dumps too much, too many ice particles are formed. They are so light that they do not fall. The overdose of dry ice merely turns the cloud of water droplets into a cloud of floating ice crystals.

* Clouds whose droplets are of water, but below the freezing point.

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