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Why do we see
hailstones in varied sizes?
Hailstones are not formed of singled raindrops. However the
process of formation of a hailstone does start with the freezing of
a single raindrop. This may be carried by a strong current to the
level where rain is still falling as drops. And as this again passes
through the cold air belt, new raindrops may cling to the frozen
hailstone, thus increasing its size. Or in other words, hailstones
grow in size by repeated
collisions with
super cooled water. This water is suspended in the cloud through
which the particle is traveling. Those single frozen
raindrops that do not get carried back to the raindrop level remain
as smaller hailstones.
The sizes of hailstones
can range from pieces with a diameter of 5 millimeters to 13
centimeters. A hailstone can even weigh up to 450 grams. Smaller
pieces, that is those with diameters less than five millimeters, are
called sleet or ice pellets.
When and where do
hailstorms occur?
Hailstorms are very common in middle
latitudes and a heavy shower generally lasts around 15 minutes. It
has been observed that hailstorms generally occur during mid to late
afternoon.
Big hailstones falling
with force are known to have caused fatal harm to human and animal
life. In an
attempt to reduce the destructiveness of hail, large quantities of
silver iodide are injected into the thunderstorm. What the
scientists are trying to do is to overseed the cloud so that many
smaller hailstones form, thereby preventing them from growing into
large destructive hailstones. However, not much headway seems to
have been done, for the results have been rather inconclusive.
Some related terms
Glaze
Sleet consists of partially frozen rain and it is formed in cold
weather when rain enters a layer of very cold air close to the
ground and freezes. However, not all the rain freezes before
reaching the ground. Sleet is usually accompanied by freezing rain
or snow. When such rain falls on cold telephone wires or tree
branches, it forms a coating of ice called glaze.
Graupel
Sometimes, falling crystals of ice may collide and get stuck to
other crystals of ice, forming snowflakes or they
may stick together to form a
chunk of icy matter called graupel.
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