Compositional Heterogeneity of Hailstones: Atmospheric Conditions and Possible Environmental Implications

© Royal Swedish Academy of Sciences 2001 Ambio Vol. 30 No. 7, Nov. 2001 http://www.ambio.kva.se Hail is precipitation in the form of balls or irregular chunks of ice, which are usually produced by convective clouds, in association with multicell, supercell, and cold fronts. Hail begins as tiny ice pellets that collide with water droplets. As the attached droplets freeze, the pellets become larger. An icy conglomeration is called a hailstone when it reaches a diameter of around 5 mm or more (1). Broadly, hailstones are the result of the updrafts and down drafts which take place inside the cumulonimbus clouds of a thunderstorm, where supercooled water droplets exist. Continued deposits of supercooled water cause the ice crystals to grow into hailstones that generally have passed through several stages of accretion, from the first stage (graupel), to small hail, to hailstones. The more times a hailstone is tossed up and down through the cloud, the larger the hailstone will be. Hailstones can reach a speed of 90 mph (140 km hr) as they fall to the ground! From 8 to 17 January 2000, numerous unusually big hailstones—weighing from around 300 g to more that 3 kg—fell in different parts of Spain under unusual atmospheric conditions (2, 3) producing damages in cars and industrial storage. Documented references regarding the fall of large blocks of ice go back to the first half of the 19th century; e.g. 1829 in Córdoba, Spain: 2 kg; 1851 in New Hampshire: 1 kg. The fall of a large hailstone, which measured 26 x 14 x 12 cm and weighed 2.04 kg, is cited, in Germany, in 1936 (4). More recently, some authors (5–8) give many other cases of large hailstones; for instance a large block of ice of almost 2 kg which fell in Kazakhistan, and one of almost one kg which fell at Strassbourg. Probably, the best-documented fall of an ice chunk was April 2, 1973 in Manchester, England. The block weighed 2 kg and consisted of 51 layers of ice. Its origin was not determined (9). For many years the largest hailstone officially reported in the United States was one that fell at Potter, Nebraska, on 6 July 1928. It had a circumference of 43 cm and weighed 680 g. This record was surpassed on 3 September 1970 at Coffeyville, Kansas, USA. The giant hailstone measured 18 cm accross, Synopsis Compositional Heterogeneity of Hailstones: Atmospheric Conditions and Possible Environmental Implications