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The formation of
ice crystals on a land surface or on exposed objects like tree
branches, plant
stems,
leaves, wires,
etc. when the temperature of the frosted object fall below freezing.
Frost, like snow,
is the result of
sublimation
(conversion of water
vapour directly to ice in saturated air). If solid surfaces in
contact with the air are chilled below the deposition point (see
freezing point), then
spicules of ice grow out from the solid surface. The size of the
crystals is a matter of time and the amount of water vapour
available. Frost develops under conditions similar to
dew, except that
the temperature is 0°C degrees or lower. There are frequently
questions as to how frost can occur when the reported temperature is
in the mid or even upper 1°C. This is because the official
thermometers are always about 1,50 m above the
ground suface. On clear, calm nights, the temperature at the
ground can be several degrees lower, thus allowing the formation of
frost.
Tender plants will suffer extensive damage or die when exposed to
frost.
Frost can be
light or
heavy and may occur in a variety of forms. When thick enough to
produce marked whitening of
vegetation
(especially grass),
it is called
hoar frost.
Frost is also used to describe the icy deposits of water vapour that
form on such surfaces as windows and windshields, which are colder
than the surrounding air and which have a temperature below freezing
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