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Water-Cloud
When as a result of the exchange of heat
and/or upward movement and exapansion,the
temperature of the air decreases so much
that the relative humidity reaches %001,
a portion of the steam molecules in the
air becomes dense ;this densitiy emerges
following cloud formation in this state
water has no longer a gaseous form , but
changes to liquid droplets or tiny suspended
solid crystals.Cloud can be considered as
a collection of liquid droplets or tiny
crystals of ice immediately after being
formed.The diameter of these droplets varies
from 2 to 100 microns usually 10 to 25
microns ,and their number in one cubic
centimeter amounts to 1000 to 2500.Almost
all clouds are formed in the troposphere
layer upto 12 km.from the ground level .
For the recognition and classification of
clouds it must first be determined how clouds
are formed in a specific time and also how
they are transformed and scattered.In general
all clouds are formed as a result of the
occurance of density in the lower layers of
the atmosphere.This happens because the humid
air climbs to the upper and middle layers
of troposphere . Different kinds of vertical
movements which take place in the atmosphere
are as follows :
1- mechanical disturbances,
2- convection ,
3- mountainous climb ,4- soft
graduall climb when the ascending current of
air is quick,the clouds produced have a high
vertical development and density . On the
contrary , if the ascending current of air
proceeds moderately and slowly , the clouds
thus produced will form layers which
depending on the amount of density , with
thick or thin strata.
Meteorologists divide clouds into four
groups usually on the basis of height :
1- upper clouds,
2- middle clouds,
3- lower
clouds,4- clouds which have vast vertical
developments the height of these clouds
in areas with average latitude is 5 to 13
km. from the ground level for upper clouds,
2 to 7 km. for middle clouds and atmost 2 km
for lower clouds .
Among all major groups of clouds,two main
ones are of immense importance,the group
known as Stratus clouds,is evolved in the
form of strate in middle troposphere,when
the existing steam cools and becomes dense,
the other group known as Cumulus forms
following the quick ascending local current
of humid air.In these clouds there is great
distance between the upper and the lower
strata.
The international cloud Atlas issued by
World Meteorological Organization WMO
contains detailed information regarding
the classification of clouds.According to
the ratification by WMO,clouds have been
divided into 4 families and 10 independent
typesthere has recently been some important
changes in the first international cloud
atlases such as the deletion of nimbuses
and the addition of nimbostratus .
Generally,the main types of clouds are as
follows :
1 - Cirrus , ci , 2 - Cirrostratus , cs
3 - Cirrocumulus,cc ,4- Altostratus ,as
5 - Altocumulus , ac , 6 - Stratus , st
7- Stratocumulus ,sc,8- Nimbostratus,ns
9 - Cumulus , cu ,10 - Cumulonimbus,cb.
At present cloud divisions have become
very vast and complicated.The division
of clouds is based on such criteria as
factor affecting their formation , the
shape and type of precipitation resulting
from them.
