Cloud Seeding Won't Prevent Rainy Olympicsby Art Rangno and Marcia Baker
Rainstorm Over Beijing, China Can weather engineers in China use cloud-seeding technology to prevent storms from brewing over the Olympics?
The scoop: Weather engineers in China plan to use cloud seeding technology upwind of Beijing to encourage them to rain and dry out before reaching the skies over the Olympic games. Will this work? We think there are a few reasons to be doubtful. First, cloud seeding specifically targets tiny droplets that are just below freezing temperatures and tend to freeze when they contact other particles. Weather engineers speed up the freezing by shooting particles (usually silver iodide crystals) into the clouds. The ice particles fall through the clouds, growing as they collide with drops that freeze to them. Some of the larger particles eventually fall out of the cloud and, if the air below isn't too dry, reach the surface as rain. But a lot of the precipitation in clouds forms at higher temperatures, where there is no ice. For example, unfrozen drops often collide with other unfrozen drops, grow to raindrop size and fall as rain. Cloud seeding with silver iodide would have no effect on forcing these drops to form sooner. Secondly, August rainfall in Beijing appears to be largely due to giant storm systems that can cover up to a hundred thousand square miles and produce rain for several hours at a time. To do anything to modify rainfall in these colossal cloud systems would be a staggering, perhaps impossible, effort. Lastly, there is no indication from any study anywhere that the kinds of deep clouds and rain systems found in China during the summertime can be modified so that the rainfall from them is significantly and predictably reduced or, conversely, increased. We doubt, therefore, that China’s weather engineering program can be relied on to produce measurable changes in Beijing’s precipitation. However -- and this is why these exercises continue all over the globe -- if little or no rain falls over the Olympic games next August or if there is a deluge, there will be no way to prove whether it was natural or due to the engineering effort. Art Rangno and Marcia Baker are retired members of the atmospheric sciences department at the University of Washington, Seattle. Both spent decades investigating cloud physics and cloud seeding. Their views are not necessarily the views expressed by Discovery Tech. If you have comments, drop me a line at tracy_staedter-cw@discovery.com |
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