An air mass is a large body of air
that has similar temperature and
moisture properties throughout.
For example, continental polar air masses ,
which originate over the northern plains of
Canada, transport colder and drier air
southward.
Maritime Tropical Air Masses
warm temperatures and rich in moisture
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Maritime tropical air masses originate over the warm waters of the
tropics and Gulf of Mexico. The northward movement of tropical air
masses transports warm moist air into the United States, increasing the
potential for precipitation.
Fronts
- the boundaries between air
masses
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Cold Front -a transition zone from warm
air to cold air
The air behind a cold front is noticeably
colder and drier than the air ahead of it.
When a cold front passes through,
temperatures can drop more than 15 degrees
within the first hour.
Warm Front
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The frontal zone slopes up and over the colder air mass
ahead of it. Warm air rides along the front (up and over the
cold air mass), cooling as it rises, producing clouds and
precipitation in advance of the surface warm front.
Because the lifting is very gradual and steady, generally
wide spread and light intensity precipitation develops
ahead of a warm front.
Think of high pressure air (like in a
balloon) escaping to a low pressure
area (like a classroom).
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Differences in pressure lead to winds.
Winds change direction due to the
rotation of the Earth
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The coriolis effect:
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A demonstration
Air Pressure on Earth
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We don’t feel air pressing on us because the
pressure in our bodies is about the same as
the surrounding air.
Air pressure is related to temperature
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Hot air has lower air pressure
Why…..?
Its molecules are moving quickly,
so they aren’t packed in together
closely
The air weighs less and exerts less
pressure.
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Cold air has higher pressure
Its molecules are packed closely
together and move more slowly.
This also explains why cold air
tends to sink.
The biggest influence on the
Earth’s weather is…
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…the sun
The sun doesn’t heat much air
directly…
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Most of the sun’s heat passes through the
atmosphere and reaches the earth.
The earth absorbs the heat and it “radiates”
back into the atmosphere.
That’s one reason why it’s colder at higher
altitudes.
Cirrus Clouds
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Cirrus Clouds
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Thin, wispy clouds that usually form above
18,000 feet
Thin because they form in the higher levels
of the atmosphere where little water vapor
is present
Made of ice crystals
Cirrus Clouds
Cirrus Clouds
Cumulus Clouds
Cumulus Clouds
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Form as water vapor condenses in strong, upward
air currents above the earth's surface
These clouds usually have flat bases and lumpy
tops
Usually very isolated with large areas of blue sky
in between the clouds
Most cumulus clouds form below 6,000 feet and
are relatively thin and associated with fair weather
Cold Front
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As the front advances, the colder air lifts the
warmer air ahead of it (red arrows).
The air cools as it rises and the moisture condenses
to produce clouds and precipitation ahead of and
along the cold front.
Upward motions along a cold front are typically
more vigorous, producing deeper clouds and more
Cumulus Clouds
Cumulus Clouds
Stratus Clouds
Stratus Clouds:
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Are thin-layered clouds
Are low to the earth’s surface
Look like stripes or streaks in the sky
Look like a layer of fog that never reaches
the ground
Cumulonimbus Clouds
Cumulonimbus Clouds:
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Are much larger and more vertically
developed than fair weather cumulus
Can easily reach 39,000 feet or higher
Are associated with powerful thunderstorms
Cumulonimbus Clouds
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Surface Map
Monday 9:00
Rain Gauge
Measures
Precipitation
(inches or
centimeters)
Anemometer
Measures
wind speed
(miles – or kilometers –
per hour
Barometer
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Barometers
measure air
pressure
A modern barometer
Thermometer
Measures
Temperature
(degrees Celsius
or Fahrenheit)
Weathervane or wind vane
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Show the direction of the wind
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