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 also poses threaten to crops and buildings.
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.