Theoretical Concept of Hail
Posted on 02. Mar, 2010 by admin in general
Introduction:
Precipitation is one form of hail. Hail in other sense means falling of balls or irregular lumps of ice (hailstones), 5 mm50 mm in diameter on average, with much larger reported from severe thunderstorms. Thunderstorms always produced by cumulonimbus. small hailstones are >5 mm in diameter. They are layered and can be irregular and clumped together.
Hail formation:
Hail forms when there is condensation nuclei such as dust, bugs, or ice crystals, when supercooled water freezes on contact. When clouds contain large numbers of supercooled water droplets, these ice nuclei grow quickly at the expense of the liquid droplets because the saturation vapor pressure over ice is slightly less than the saturation vapor pressure over water. When the hailstones grow large enough, latent heat released by further freezing may melt the outer shell of the hailstone. The growth that follows is called wet growth, which is usually more efficient because the liquid outer shell allows the stone to accrete other smaller hailstones in addition to supercooled droplets. These winds hold the rain and freeze it. As the process repeats, the hail grows increasingly larger
Ideal conditions for hail formation:
1. When there are strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing (< 32 °F (0 °C)). The growth rate is maximized at about -13 °C (9 °F) then hail forms.
2. during early summer where surface temperatures are warm enough to promote the instability associated with strong thunderstorms, but the upper atmosphere is still cool enough to support ice. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the midlatitudes because the atmosphere over the tropics tends to be warmer over a much greater depth. Then hail forms.
3. also when dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in.
Deadly hailstorms:
1. several hundred pilgrims were killed by a massive hailstorm in Roopkund, Uttaranchal, India.[4].
2. $150 million in damage when softball-sized hail hit Calgary, Canada on July 28, 1981.
3. Softball-sized hail destroyed roofs and cars, causing $625 million in total damage in Denver, Colorado, USA.
4. a Labour Day thunderstorm caused $400 million worth of insurable damage in Calgary, Canada. Thirteen additional hailstorms between 1981 and 1998 caused an estimated $600 million in damage in the Calgary area alone.
5. Dallas and Fort Worth, Texas, USA, $1.1 billion insured losses on May 5, 1995.
6. $1.6 billion. 20,000 properties and 40,000 vehicles were damaged during the storm with more than 25 aircraft damaged at Sydney Airport, one person was killed while fishing after getting struck by lightning and several other people were injured. It was the costliest hailstorm to hit an Australian populated city on April 14, 1999 in New South Wales, Australia.