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Science/Tech See other Science/Tech Articles Title: Rain? Blame it on the Plane Aircraft may produce holes in clouds and cause an unusual phenomenon that results in increased rain or snowfall in the area immediately around the world's major airports, a new study suggests. Flying aircraft may punch holes in clouds and cause an increase in precipitation according to a new study. Kelsey Hubbard gets the details from WSJ's Gautam Naik. A flying plane "can freeze the water drops in a cloud and produce a ribbon of ice crystals" behind it, said Andrew Heymsfield, lead author of the paper, to be published in the journal Science on Friday, and a cloud physicist at the National Center for Atmospheric Research in Boulder, Colo. The icy ribbon may then expand across a few miles and result in a narrow band of rain or snow. The physics behind this event is similar to what happens in so-called cloud seeding, where a chemical such as silver iodide is dispersed into clouds to influence the amount of precipitation falling from them. The introduced particles act like nuclei around which the water vapor condenses, eventually falling as rain or snow. The Beijing Weather Modification Office famously used the seeding technique to drain clouds ahead of the opening ceremony of the 2008 Olympics, though it is unclear whether the lack of rain during the event was due to human action or good luck. It turns out that if conditions are right, both jet and turboprop aircraft can inadvertently seed clouds as well, possibly influencing the local weather. View Slideshow [SB10001424052702304584004576417940024451416] There are limited examples linking the flight paths of aircraft to heavier snowfall near airports. One case is based on radar measurements taken near the former Stapleton Airport in Denver. The 1992 data show heavier snow falling in bands aligned to the flight path of four aircraft, compared with lighter levels of snow in other areas. Dr. Heymsfield hopes to perform additional studies to establish whether there are greater amounts of aircraft-induced snow near major airports, rather than further away from them. Water drops contained in a cloud often exist in a super-cooled state between 0 degrees Celsius (32 degrees Fahrenheit) and minus 40 degrees Celsius. When a plane flies through the cloud, it can expand the air, thereby cooling it, sometimes by as much as 30 degrees, according to Dr. Heymsfield. This additional cooling can turn the water into ice. Circulation effects within the cloud help expand the initial ribbon of ice crystals, producing a hole or channel through the cloud, which after several hours can cover a large area. The resulting rain or snow falls below. Such odd-shaped clouds have been observed for years. When a saucer-shaped cloud hovered ominously over Moscow in 2009, it triggered speculation about rocket launches and UFOs. It was most likely a "hole-punch" cloud caused by aircraft, scientists say. In 1983, Arthur Rangno, a flight meteorologist at the University of Washington, Seattle, co-authored a paper in which he and a colleague described how their research plane had apparently produced ice while traveling through a cloud. Many scientists "were reluctant to accept our results," says Mr. Rangno, now retired, because the cloud's temperature was only minus 8 degrees Celsius—far from the minus 40 Celsius at which ice forms in clouds. In 2007, Dr. Heymsfield was in a research plane flying over Colorado and studying how ice and snow crystals begin in clouds. Radar on the ground, meanwhile, picked up an "echo" suggesting a band of strong storms in the area. However, neither the airborne scientists nor the plane's myriad instruments picked up any such sign. When Dr. Heymsfield checked the plane's video footage, he was surprised. "We saw the hole left by the plane and snow falling through it," he recalls. "But it wasn't snowing from the rest of the cloud." Dr. Heymsfield then discovered that two turboprop aircraft had flown up through the cloud 40 minutes earlier; soon after, snow had fallen in a narrow band 20 miles long and 2.5 miles wide, leaving an inch of snow on the ground. In a study published last year, Dr. Heymsfield and his colleagues concluded that aircraft could, indeed, influence the local weather. The latest research extends those findings. Dr. Heymsfield and his team analyzed 20 satellite images of a hole-ridden cloud that was suspended over Texas in January 2007. Some of the holes were visible for more than four hours and grew to more than 60 miles long. Data on airplane traffic in the area indicated that various types of aircraft—from single-engine jets to turboprops and commercial jetliners—could produce such holes in super-cooled clouds. Finally, satellite data revealed that super-cooled cloud layers could be found within 62 miles of the world's biggest airports as much as 5% to 6% of the time. "The study is convincing," says Greg McFarquhar, an expert on cloud physics at the University of Illinois at Urbana-Champaign, who read the paper but wasn't involved in the research. "We now need to understand how often these types of cloud occur, and how better to forecast the conditions" for aircraft-induced snow. Mr. Rangno was more cautious. "I think the idea of precipitation occurring around airports is overstated," he said. Planes approaching an airport may be scores of miles away when they fly through clouds, so any snow could fall a long way off, Mr. Rangno said. Winds, too, could push the snow away from airports. Write to Gautam Naik at gautam.naik@wsj.com
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#1. To: Ada (#0)
Once clouds form, just about any disturbance, especially the addition of something tangible, can trigger rain. Often it's dust that causes the droplets to cluster and develop some weight. One thing that has been demonstrated NOT to produce rain: Having Texas Gov. Rick Perry pray for it.
And one thing has been proven not to bring any sunshine to the American economy, is having a Obama in the White House.
"The person who agrees with you 80 percent of the time is a friend and an ally — not a 20 percent traitor" - Ronald Reagan
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