What's Behind a Cloud
Monday April 24, 2006
Spring is a great time of year to lie back in the grass and enjoy some beautiful cloud formations. Read here to learn how to interpret what you see.
Spring is a great time of year to lie back in
the grass and enjoy some beautiful cloud formations. Clouds are not just fun to
look at, but they can also give us a clue about our weather. The different
types of clouds are all formed in different ways and bring different types of
weather.
There
are three types of clouds. It is easy to forget which cloud is which. It will
help to learn the Latin roots of cloud names. Clouds are named for their appearance
and for how low or high they are in the sky. The three main types of clouds are cirrus,
cumulus and stratus.
Cirrus means curl in
Latin. Cirrus clouds are shaped like thin curls of hair and are found very high
in the sky. These clouds are made of ice crystals, even in the summer. Cirrus
clouds are found above 20,000 feet. At this height it is cold, and the water
droplets that make up the cirrus clouds freeze. Cirrus clouds can be an early
warning that thicker rain clouds are coming in a few days.
Cumulus
means heap in Latin. Cumulus clouds look like “heaps” of cotton balls and they
are found low in the sky. These clouds are always changing shape, but are
usually as tall as they are wide. Cumulus clouds are fun to watch because they
can take the shape of anything you can imagine and are a sign of good weather.
If cumulus clouds begin to build in the middle and rise they are called
cumulonimbus. Nimbus means rain in Latin. Cumulonimbus clouds are tall, dark,
and can bring lightning, rain, hail, and even tornadoes.
Stratus means layer or cover in Latin. Stratus
clouds occur in low, thin layers that can cover the whole sky. If the layers
are broken apart, they are called stratocumulus. Stratus clouds can thicken and
darken, but then they are called nimbostratus and can bring rain.
Clouds
are formed when water vapor in the air turns into water droplets or ice. This
process is called condensation. For condensation to happen there must be enough
water in the air, the air must cool enough, and there has to be a surface for
the water vapor to form on. For a surface, the water droplets use microscopic
particles in the air. These particles can be in the form of dust, smoke, soot,
even salt. As water vapor in the air cools, they begin to collect on the
particles in the air and form clouds. If the droplets become too heavy, they
fall as rain or snow.
What
gives clouds their color? The water droplets that make up a cloud are dense.
Sunlight cannot pass through the cloud and is reflected. This gives clouds their white color.
If the droplets in a cloud begin to combine, more space is created between the
droplets. More light can now penetrate the cloud and less light will be
reflected. When this happens clouds can appear various shades of grey. As the water
droplets get larger, more space is created and the cloud will be dark grey.
When the droplets become too large, they will fall as rain. The darker the
cloud, the more likely it is there will be rain. Some storm clouds may be
greenish. This green color is caused when sunlight is scattered by ice in the
clouds. A greenish cumulonimbus cloud will most likely bring severe weather in the form of rain, hail, or possibly tornados. At
sunrise and sunset, clouds often appear to be shades of red, pink, and orange.
These colors are the result of the scattering of light by the atmosphere.
Shades of red and orange have long wavelengths in the visible spectrum. Blue
and green have wavelengths. Short rays are easily scattered, while longer rays
are easily absorbed. When clouds appear red, pink, or orange, they are reflecting
the long rays of sunlight that are common at sunrise or sunset. It is the same
as shining a red light on a white sheet. The sheet only appears to be red.
Clouds occasionally appear to be yellow. Yellow means there is smoke present.
If there is a forest fire in your area, clouds will yellow in color.
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