Geoscience Reference
In-Depth Information
Figure 11.6
Basic forms of
solid precipitation, from top
to bottom, plate, stellar
crystal, column, needle,
spatial dendrite, capped
column, irregular crystal,
graupel, ice pellet, and
hailstone.
precipitation is created. Snow and sleet (sleet being just melting snow) generally
originate in low or multi-layer stratiform clouds in cold weather. As a result, their
occurrence is usually more widespread than other forms of frozen precipitation
and they tend to occur over longer duration. The other types of frozen precipita-
tion are different forms of ice particles. These can be produced from a wide range
of clouds, but because ice pellets and hail are mainly produced by clouds in which
convection is important, they tend to be more intense and more localized than
frozen precipitation which falls as snow. Figure 11.6 illustrates some of the basic
forms of solid precipitation together with the symbols and codes meteorological
observers use to represent them.
Other forms of precipitation
In its most general sense, the word precipitation can include the release of water
from the atmosphere to the ground or to vegetation on the ground in liquid or
solid form by any mechanism. Clouds are not necessarily an intermediary.
Although the precipitation provided by alternative processes does not necessarily
make a major contribution to the water cycle at the global scale, it can make a
significant seasonal contribution at local and perhaps regional scale in particular
locations.
Dew and frost are notable alternative forms of precipitation, which in moist,
cool climates can have significant influence on the water balance in the winter
season. In many cases the amount of water deposited as dew or frost during a
