Download Cloud Formation

Cloud Formation
Ingredients Required for Clouds:
Water vapor (water as a gas)
Cooling (change of the state: from gas
to liquid or ice)
CONDENSATION
A surface for water vapor to condense on
(condensation nuclei)
How does the water get into the air?
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E
E
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By evaporation and transpiration
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CONDENSATION
Sunlight causes water to evaporate into the atmosphere.
This air containing the water vapor is heated at the surface of the earth and rises.
As the air rises, it cools and the water vapor condenses on some form of particulate
matter such as dust, ash, or smoke to form clouds. The particulate matter are called
Condensation Nuclei.
Condensation on spider webs.
Views of early morning fog in Indiana
Importance of Clouds
• So, what is a cloud?
It is a thick mass of suspended water drops or ice
crystals.
• What do clouds tell us?
The presence of clouds in the sky is one type of signal
to meteorologists that there will be changes in the
weather. Predicting the weather requires the
understanding of the different types of clouds
Cloud droplet formation
• If the air temperature cools below the dew point, water vapor
will tend to condense and form cloud/fog drops.
• As with dew and frost, cloud drop formation prefers to
condense on a surface of some sort - we call these particles
cloud condensation nuclei. Without these particles clouds
would not form.
• Terrestrial Sources
– Dust/sand/dirt particles
– Smoke - volcanic, fires, and pollution
– Pollens and spores
• Oceanic Sources
– Sea Salts
Typical sizes
Dew
• Surfaces cool strongly at
night
– Strongest on clear, calm
nights
• If a surface cools below the
dew point, water condenses
on the surface and dew
drops are formed
Frost
• If the temperature is below
freezing, the dew point is called
the frost point
• If the surface temperature falls
below the frost point water
vapor is deposited directly as
ice crystals
• The resulting crystals are
known as frost, hoarfrost, or
white frost
What factors result in cloud formation?
1. The air must rise
2. As the air rises, it encounters less pressure.
The air molecules expand and cool
(Adiabatic Cooling)
3. When the air is cooled to the dew point
temperature condensation occurs and clouds
begin to form
What causes the air to rise?
• Forced up over a mountain range
Air rising and cooling to the dew point by expansion (adiabatic
cooling)
Pictures from the National Audubon Society Field Guide to Weather
What causes the air to rise?
• Convection current
The Sun heating the ground,
which then heats the air above,
which then rises due to
convection (is less dense than
the cooler air surrounding it.)
What causes the air to rise?
• A mass of relatively low density is forced up
and over a mass of cooler, more dense air
This happens at the boundaries between AIR MASSES
AIR MASS: A
region of air that
has similar
temperature and
moisture.
Fronts: boundary
that separates 2
different air
masses
4 Types of weather fronts:
Cold Front
Stationary Front
Warm Front
Occluded Front
Cold Front
Fast moving cold air mass runs into a slow
moving warm air mass and the thicker cold air
slides under the lighter warmer air.
A cold front symbol
The direction that the teeth point
indicate the direction the front is
moving.
Weather: showers and thunderstorms
Warm Front
Moving warm air mass
collides with a slowly moving
cold air mass and the warm air
moves over the cold air.
Warm Front symbol
The directions that
the bumps face is the
direction the front is
moving.
Weather: fog, rain or snow
Stationary Front
Cold air mass and warm air mass meet, but
neither air mass has enough force to move the
other air mass.
Stationary Front Symbol
blue triangles point in the
direction of the warmer air
Occluded Front
Warm air mass is caught between two cooler
air masses and the thicker cold air masses
move underneath the thinner warm air mass
and push it upward.
Occluded front symbol
The directions that the bumps face
is the direction the front is moving.
Weather: rain, possible thunderstorms
Which types of fronts can you find on
this map?