Formation of Clouds
• A cloud is composed of millions of little droplets of water (or
ice crystals when temperature is very low) suspended in the
air.
• There are several major processes for cloud formation.
• Convection
• Forceful Lifting
• Meeting air masses
• Horizontal motion
Convection :
• When the sun shines, the air at the ground
level that contain water vapor is heated and it
begins to rise, and as the air rises, it begins to
cool.
• The water then condenses on tiny suspended
particles and forms droplets in the
atmosphere.
Convection:
Forceful Lifting (mountains)
• When air rises over the mountains, it cools
and becomes saturated with water vapor.
Condensation occurs and the water vapor
becomes liquid.
• When the air mass descends on the other
side of the mountain, it is more dry and warm.
Meeting of air masses
• Not only mountains can force air to rise :
when warm air meets a mass of heavier cold
air, it is also forced to rise. The boundary
between warm and cool air is called a « front
». As the warm air ascends it cools, and then
clouds may be formed.
Horizontal motion
• Sometimes winds bring warm and moist air
into a region. If the warm moist air flows over
a much colder surface, it is cooled and
moisture will condense and form fog. This
mechanism is frequent on the coast of
continents.
Types of Clouds
• Clouds are classified according to their height
above and their appearance from the ground.
The following cloud roots and translations
summarize the components of this
classification:
•
•
•
•
•
Cirro- curl of hair, high altitude
Alto- middle altitude
Strato- form in layers
Nimbo – rain, precipitation
Cumulo - heap
High Level Clouds
• High level clouds occur above 20,000 feet and
are given the prefix “cirro.” Cold tropospheric
temperatures the clouds are composed of ice
crystals.
• Three main types: cirrus, cirrostratus, and cirrocumulus
Mid-level clouds
• Appear between 6,500 and 20,000 feet.
• Depending on the time of year, temp and
altitude these clouds may be composed of
liquid water droplets, ice crystals, or a
combination of the two.
– Two main types are: altostratus and altocumulus
Low-level clouds
• Not given a prefix.
• Low clouds occur below 6500 feet and
normally consist of liquid water droplets or
even supercooled droplets, except during cold
winter storms when ice crystals comprise
much of the clouds.