Air Masses, Geography and Weather.

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Air Masses, Geography and Weather.

• Note-taking Required
• (Use the Cornell Method)

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Analysis of weather data shows

• Regions near oceans tend to have moderate
  temperatures.
• Regions distant from oceans tend to have extreme
  temperatures.
• Regions near oceans tend to have high annual
  rainfall.
• Regions distant from oceans tend to have low
  annual rainfall.

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What accounts for these general climate trends?

• The formation and movements of air masses.
• The influence of topography on the movement and
  characteristics of air masses.
• Seasonal changes resulting from the effect of
  latitude on the duration and angle of sunlight.

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Vocabulary to know

• Air Mass - a region of the atmosphere that has
  specific temperature and moisture characteristics
• Maritime (or marine) air mass - An air mass that
  forms over oceans and is therefore a wet air mass
• Continental air mass - An air mass that forms
  over land and is therefore a dry air mass

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More important terms

• Tropical air mass - An air mass that forms at low
  latitude, and is therefore a warm air mass
• Polar air mass - An air mass that forms at high
  latitude, and is therefore a cold air mass.
• We combine pairs of terms to describe any given
  air mass based on temperature and moisture
  characteristics.

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Four kinds of air masses

• Maritime tropical air mass - A warm and wet air
  mass, forming over low latitude oceans.
• Maritime polar air mass - A cold and wet air
  mass, forming over high latitude oceans.
• Continental tropical air mass - A warm and dry
  air mass, forming over low latitude land.
• Continental polar air mass - A cold and dry air
  mass, forming over high latitude land.

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Other facts about air masses

• Maritime air masses do not tend to get as warm or
  cold as continental air masses.
• Why?

Ocean water acts as a temperature regulator for
the air above the surface of the ocean.
If the air above the ocean is colder than the
ocean water, the water will give away heat
energy to the air, preventing the air from
becoming too cold.
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If the air above the oceans surface is warmer
than the ocean water, the water will take away
heat energy from the air, preventing the air from
becoming too warm.
So, the ocean acts sort of like Natures
Thermostat, keeping air temperatures near oceans
at more moderate temperatures than the air
temperatures experienced in areas far from the
influence of the ocean.
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Continental air masses can get extremely hot and
extremely cold.
Why do continental air masses experience
temperature extremes?
Because continental air masses form in regions
that are separated and protected from the
moderating influence of ocean water.
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Where do air masses form, and what factors
separate and protect some regions from the
influence of the oceans?
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North America is generally affected by six
different air masses
Continental Polar cP (Canada)
Maritime Polar mP (Gulf of Alaska)
Maritime Polar mP (North Atlantic)
Continental Tropical cT (Desert Soutwest)
Maritime Tropical mT (South Pacific)
Maritime Tropical mT (South Atlantic and Gulf of
Mexico)
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Local weather conditions are a result of the air
mass that is affecting our area.
Maritime Polar Air (cold and damp)
Weather that is cold and damp is the result of
Maritime Polar air moving from the Gulf of Alaska
over the Pacific Northwest. Typical Maritime
Polar weather is cold (in the 40s in winter and
60s in summer) with clouds and/or fog and high
humidity, or dampness.
Maritime Polar Air (cold and damp)
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Local weather conditions are a result of the air
mass that is affecting our area.
Weather that is warm and damp is the result of
Maritime Tropical air moving from the South
Pacific over the Pacific Northwest. Typical
Maritime Tropical weather is warm (in the 50s in
winter or 70s in summer) with clouds and/or fog
and high humidity, or dampness.
Maritime Tropical (warm and damp)
Maritime Tropical (warm and damp)
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Local weather conditions are a result of the air
mass that is affecting our area.
Weather that is cold and dry is the result of
Continental Polar air moving from Canada over the
Pacific Northwest. Typical Continental Polar
weather is cold (in the 30s in winter or 70s in
summer) with clear skies and very dry conditions.
Continental Polar (cold and dry)
Continental Polar (cold and dry)
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Local weather conditions are a result of the air
mass that is affecting our area.
Weather that is warm and dry is the result of
Continental Tropical air moving from the Desert
Southwest over the Pacific Northwest. Typical
Continental Tropical weather is warm (in the 60s
in winter or 90s in summer) with clear skies and
very dry conditions.
Continental Tropical (warm and dry)
Continental Tropical (warm and dry)
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Storms occur when air masses interact with each
other.

• A Weather Front occurs when one air mass
  collides with another air mass.
• A Warm Front occurs when a warm air mass
  collides with and replaces a cold air mass.
• A Cold Front occurs when a cold air mass
  collides with and replaces a warm air mass.

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A typical warm front occurs when a maritime
tropical air mass collides with a continental
polar air mass.
Warm maritime air moves into a region that has
been occupied by cold continental air.
Cold Continental Air
Warm Maritime Air
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Warm fronts cause clouds and steady rain.
Less dense warm air pushes over the top of the
more dense cold air. As the warm air is lifted
up, water vapor in the air condenses to form
clouds and rain. Eventually the warm air will
push out the cold air, leaving the warm and
damp weather conditions typical of a maritime
tropical air mass.
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A typical cold front occurs when a maritime polar
air mass collides with a continental tropical
air mass.
Cold maritime air moves into a region that has
been occupied by warm continental air.
Warm Continental Air
Cold Maritime Air
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Cold fronts cause clouds and heavy, showery rain.
More dense cold air bulldozes underneath the
less dense warm air. As the warm air is shoved
upward, water vapor in the air condenses quickly
to form cumulus clouds and heavy rain.
Eventually the cold air will push out the warm
air, leaving the cold and damp weather conditions
typical of a maritime tropical air mass.
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Why does Western Washington get more rain than
Eastern Washington?
Orographic Lifting Orographic lifting occurs
when moving air encounters mountains. The air is
forced upward, causing cooling and condensing of
moisture. The moisture falls out of the
atmosphere as rain on the windward side of the
mountains.
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Orographic Lifting also produces the dry
conditions in Eastern Washington
As air rises up the west sides of mountains, the
air cools and moisture condenses into rain. By
the time the air reaches the top of the mountains
it has lost most of its moisture. The drier air
now descends down the east slopes of the
mountains. As the air descends it warms, and
absorbs moisture instead of releasing it. The
result is very dry conditions on the east sides
of mountains. These dry regions east of the
mountains are called rain shadows. How extreme
a rain shadow will be depends on how far the
region is from the ocean, and how high the
mountains are that separate the area from the
ocean.
Rain shadow Animation