Hail disaster is a severe meteorological disasters caused by the strong convective weather systems. Even through the affected scope of hail is relatively small, and its lasting time is also short, it is still fierce and has great intensity, accompanying by strong winds, heavy rainfall, rapid cooling and paroxysmal disastrous weather process.
Hail is formed in the cumulonimbus which caused by convective cloud. The rising vapor alone with the airflow liquefies when it goes up, which means a lower temperature. And when it comes below zero degrees Celsius, drops of water freeze into ice which will absorb other ice particles and drops so as to gain weight to fall into some higher temperature area, melting into some droplets that will also absorb circumambient droplets. It can be lifted up again if it has encountered strong updraft, and will catch up more water particles once again until it weighs more than aerostatic buoyancy and landed. If solid ice particles have not dissolved into water when they are down to the ground, they can be called hail.
Hail disaster, a kind of sudden natural calamity, is a soild precipitation with the shape of sphere or conic, formed by clear layer and opaque layer. The diameter of these ice paticals comes as 5 to 50 mms, or even 10 cms. As for those whose diameter is shorter than 5mms, they usually be called graupel.
The hail usually measures its diameter, hail time, and hail thickness.
Slight hail: less than 0.5 cm diameter; less than 10 min; less than 2cm thickness.
Medium hail: 0.5 - 2cm diameter; 10 – 30 min; 2 – 5cm thickness.
Strong hail: over 2 cm diameter; over 30min; over 5 cm thickness.
Hail disaster is a kind of severe weather disasters caused by strong convective weather system. Although the scope of appearing is small and the time is short, yet it is really fierce with strong intensity. Besides, it is often accompanied by fierce winds, heavy rain, and a sharp cooling and other paroxysmal disaster weather process. China is a country with frequent hailstorm disasters. The hailstorm has caused huge losses to agriculture, construction, communication, electricity, transportation and people's life and property every year. According to relevant statistics, the economic losses caused by hail disasters in China reaches up to several hundred million yuan or even several billion yuan each year.
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