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CLOUDS
What is a cloud?
Scientists define clouds as visible masses of
droplets, frozen water floating in the Earth’s
atmosphere that you can see from the ground.
Another way to think of this is a cloud is a large
collection of very tiny droplets of water or ice
crystals. The droplets are so small and light that
they can float in the air.
How are clouds formed?
• All air contains water, but near the ground it is
usually in the form of an invisible gas called
water vapor.
• When warm air rises, it expands and cools. Cool
air can't hold as much water vapor as warm air,
so some of the vapor condenses onto tiny pieces
of dust that are floating in the air and forms a
tiny droplet around each dust particle.
• When billions of these droplets come together
they become a visible cloud.
Why do clouds float?
A cloud is made up of liquid water droplets. A
cloud forms when air is heated by the sun. As
it rises, it slowly cools it reaches the saturation
point and water condenses, forming a cloud.
As long as the cloud and the air that its made
of is warmer than the outside air around it, it
floats!
Types of Clouds
Clouds are classified into three basic
categories, depending largely on the
height of their bases above the ground.
High AltitudeClouds:
Cirrus
• Cirrus means “curl of hair.”
• Cirrus clouds appear feathery or
wispy.
Cirrus Clouds
• Cirrus clouds form in very cold air at high
altitudes.
• Made of ice crystals, they have wispy or feathery
appearance.
• Strong winds often blow streamers or “tails” off
cirrus clouds.
• Theses features show the direction of the wind.
• You will usually see cirrus clouds in fair weather.
However, they can be a sign that a storm is
approaching.
Middle Altitude Clouds:
Cumulus
• Cumulus means “heap” or
“pile.”
• Cumulus-type clouds can grow
to be very tall.
Cumulus Clouds
• Cumulus clouds are puffy white clouds with
darker bases.
• They look like cotton balls floating in the sky.
• There are several varieties of cumulus clouds.
• Usually they appear in the daytime in fair
weather, when warm air rises and its water vapor
condenses.
• Cooler air sinks along the sides of the clouds,
keeping cumulus clouds separate from one
another.
Cumulonimbus Clouds
• The tallest clouds are cumulonimbus clouds, or
thunderheads.
• These clouds produce thunderstorms that drop
heavy rainfall.
• A cumulonimbus cloud can tower 18 kilometers
above Earth’s surface.
• By comparison, jet planes usually fly at about 10
kilometers.
• Strong high-altitude winds often cause the top of
the cloud to jut out sharply.
Low Altitude Clouds:
Stratus
• Stratus means “spread out.”
• Stratus-type clouds form in flat
layers
Stratus clouds
• Stratus clouds form in layers when air cools over
a large area without rising or when the air is
gently lifted.
• Stratus clouds are smooth because they form
without strong air movement.
• Stratus clouds that form at high altitudes are
much thinner than low stratus clouds.
• The ice crystals in high stratus clouds can make it
seem as if there’s a circle of colored light around
the Sun or Moon.
Fog
• Fog is a cloud that rests on the ground.
• Like stratus clouds, fog has a smooth appearance.
• It usually forms when a surface is colder than the
air above it.
• Water vapor in the air condenses as it cools,
forming a thick mist.
• Fog on land tends to be heaviest at dawn, after
the ground has cooled overnight.
• It clears as the ground is heated up by sunlight.
Clouds with vertical development:
Cumulus Clouds
• Cumulus clouds are puffy clouds that sometimes look like pieces of
floating cotton. The base of each cloud is often flat and may be only
1000 m (330 ft) above the ground. The top of the cloud has
rounded towers. When the top of the cumulus resembles the head
of a cauliflower, it is called cumulus congestus or towering cumulus.
These clouds grow upward, and they can develop into a giant
cumulonimbus, which is a thunderstorm cloud.
•
Cumulonimbus clouds are thunderstorm clouds that form if
cumulus congestus clouds continue to grow vertically. Their dark
bases may be no more than 300 m (1000 ft) above the Earth's
surface. Their tops may extend upward to over 12,000 m (39,000
ft). Tremendous amounts of energy are released by the
condensation of water vapor within a cumulonimbus. Lightning,
thunder, and even violent tornadoes are associated with the
cumulonimbus.
Create your own cloud!