Austria
Hail Suppression Aircraft Outsmart Nature
The SÜDFLUG company has been using aircraft to suppress hail in the Austrian state of Styria since 1982. As part of a longstanding partnership, Brenntag supplies the substances necessary for the company’s cloud seeding activities.
Photo: Brenntag
During the hot period of the year, storms act like gigantic power plants. Hot air rises or is lifted by flows of cold air. As it cools, the water vapor is transformed into tiny water droplets at what is known as the condensation level. The condensation process releases heat, causing the droplets to rise to even higher elevations. While it is often more than 30°C at ground level in the summer, the temperature at an elevation of 7 to 8 kilometers can be as cold as -25°C. Starting at elevations of 4,000 m, snowflakes form on naturally occurring dust particles in the air and are carried even higher by strong updrafts. The water droplets remain liquid up to 8,000 m at temperatures as low as -20°C. If they fall to the ground, dangerous black ice forms due to the immediately freezing rain. The rising snowflakes attract the super-cooled water droplets like a magnet, which results in hailstones. The hailstones also fall toward the ground, but are blown upwards again by the strong updrafts. This process makes them grow until they precipitate in the form of heavy hail. This hail can cause serious damage when it reaches the earth. Crops may be destroyed, cars, buildings and roofs may sustain heavy damage, and humans and animals can be injured. And extreme weather is more common during times of climate change. In the “record year” of 2008, it hailed on 135 days in Germany alone. Damages in Austria in 2008 were in the billions of euros, according to media reports. For the past 27 years, SÜDFLUG has not observed a single hail catastrophe in the region where its hail suppression aircraft operate. Before hail suppression measures were implemented, a single hailstorm caused more than EUR 22 million of damage in 1980. Since the inception of the program, the protected area has been quadrupled in size to include several neighboring regions. “We estimate that our cloud seeding program has prevented damages of approximately EUR 800 million,” reports Walter Golob, manager of the twelve hail-suppression aircraft at SÜDFLUG. “We are very proud of our work.” Silver Iodide As The “Silver Bullet” The hail suppression method used in Austria rely on aircraft to disperse substances into the air in hail-prone storm zones to serve as ice nuclei in addition to the naturally occurring condensation particles. This helps distribute the super-cooled water across numerous small hailstones. Ideally, these small stones melt on their way to the earth, where they impact in the form of heavy drops or slush without causing any damage. Silver iodide is the “silver bullet” used to prevent hail. This compound consists of silver and iodine, which as a solid is in the form of yellowish crystals. The major advantage of silver iodide is that it has no negative characteristics because it does not react with the environment. When used in cloud seeding, it falls to the ground with the rain or snow, where it is broken down by organic acids into its constituents of silver and iodine. Studies by the University of Graz in Austria were unable to detect either substance at the ground level. SÜDFLUG has installed burners on its aircraft to directly and effectively disperse the silver iodide in storm zones where hail develops. Cloud seeding requires outstanding flying skills because the strong winds at the cloud level can have unpredictable effects on the stability of the small airplanes. Four hail suppression aircraft are in operation in Styria from May to September, each equipped with two burners, silver-iodide containers of up to 100 liters and as many as 6 flares. The airplanes can remain airborne up to 7.5 hours, which is essential for effective seeding of large, persistent storms. They are also capable of flying at night. If potential danger from hail arises, the pilots in the deployment center are notified of when and where to fly and how much material to disperse in the protected area. This information is provided by a meteorological service, which monitors developments day and night via radar and online satellite images. Because storms can arise quite quickly, the pilots must often take off within minutes of notification. In case of storm threat, a pilot is always on duty in the deployment center 30 meters away from the aircraft. Golob adds: “It is essential to react to storm clouds in a timely manner, because once hailstones form, even silver iodide cannot dissolve them.” In addition to suppressing hail, the special aircraft are also used for seeding snow and rain and clearing fog. To ensure rain-free Olympic Games in summer 2008 for instance, the Chinese government deployed hail suppression aircraft and silver iodide. Brenntag has been working with SÜDFLUG for more than 27 years. Contact: Monika Abraham-Wohl monika.abraham@brenntag.at Further information:www.suedflug.at
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