Download The Atmosphere in balance

Mr. Lanik, Ms. Cooley, Mr. Liebowitz
Vocabulary
Meteorology
 Air Mass
 Front
 Cold Front
 Warm Front
 Occluded Front
 Stationary Front

Meterology

The study of the
process that makes
up the Earth’s
atmosphere and
what helps make
weather predictions.
Air Mass

A large body of air
that has similar
characteristics
throughout it.
Front

The boundary (line)
that separates
different air masses.
Cold Front

The line between an
advancing cold air
mass and the
warmer air mass it is
moving.
Warm Front

The line between
the advancing warm
air and the cold air
mass it is moving.
Occluded Front

When a cold front
“catches up” to a
warm front.
Stationary Front

If a front (cold or
warm) is not moving
forward.
Guided Notes
An air mass is a large
body of air in the
lower troposphere that
has similar
characteristics
throughout.
 An air mass can be
several thousand
kilometers in diameter
and several
kilometers high.
 Two or three air
masses can cover the
entire U.S.!

Guided Notes
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Throughout an air mass,
 temperature
and
 Humidity are nearly uniform.
The temperature and humidity of an air mass
depends on where the mass originates.
In polar regions the lack of sunlight causes the
ground to be very cold.
If an air mass stays in a polar region for a long time,
the air mass becomes cold.
The opposite happens in tropical regions.
Guided Notes
The moisture of an air mass depends on
the surface where it came from.
 If an air mass stays over land for a long
period of time, it becomes dry, where an
air mass over the ocean absorbs water
vapor and becomes moist.

Guided Notes
When an air mass moves from one place
to another, it takes the temperature and
humidity of its place of origin with it.
 However, some of its characteristics may
change as it moves across the country.
 When cold polar air moves south, it affects
the weather of the area it enters, as well as
slowly heats up as it moves across a
warmer surface.
 Earth’s topography also helps change the
temperature and humidity of an air mass as
it travels.

Guided Notes

There are five main air
masses in North
America:
 Continental Arctic
 Continental Polar
 Maritime Polar
 Maritime Tropical
 Continental Tropical
Guided Notes
Continental Arctic (cA) air masses
originate in the arctic regions where the
air is extremely cold.
 Because cold air is incapable of
containing much moisture, cA air
masses are very dry.

Guided Notes
Continental Polar (cP) air masses start
over Alaska and Canada and are
somewhat warmer than the cA air masses.
 The differences in temperature and
humidity between cA and cP air masses
are usually slight.
 When cP air passes over the Great Lakes
region in the late fall when the water is still
warm, the cold, dry air picks up moisture
from the lakes, then dumps the
precipitation as snow, causing lake effect
snow.

Guided Notes
Maritime Polar (mP) air masses form over
the ocean in high latitudes. These air
masses are both cold and damp.
 mP air is not as cold as cP air because of
the difference in temperatures between the
land and the oceans.
 Occasionally mP air rom the North Atlantic
brings heavy snowstorms called
nor’easters to the East Coast in the winter
and cool, clear weather to the area in the
summer.

Guided Notes
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Maritime Tropical (mT) air masses form over warm
tropical ocean and gain both warmth and moisture.
In the summertime, mT air from the Bahamas and
the Gulf of Mexico moves counterclockwise around
the low pressure over the Atlantic Ocean, bringing
heat and humidity to the Midwest and Eastern U.S.
Since the air mass contains a lot of moisture,
thunderstorms often develop.
As the sun heats the ground, the moist mT air is
heated from below and rises, forming thunderclouds.
When the sun sets, the clouds and thunderstorms
leave as the surface cools.
Guided Notes
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Continental Tropical (cT) air masses originate over the
deserts and are hot and dry.
Most of the time a cT air mass originates as a maritime air
mass but becomes dry as it passes over mountains.
cT air masses produce massive heat waves in most of the
United States.
mT air usually produces temperatures no higher than 100
degrees Fahrenheit, but cT air is much hotter, with
temperatures exceeding 100 degrees Fahrenheit.
cT air is dry and does not bring clouds of thunderstorms,
however if this type of air mass comes into a crop region it
can cause serious damage to them.
Guided Notes
Air masses of different
types do not mix easily.
 The boundary that
separates different air
masses are called
fronts.
 The width of a front can
range from 200 meters
to 200 kilometers and
can effect weather
patterns in areas
hundreds of kilometers
wide.

Guided Notes
Fronts are most common at midlatitudes, where southward moving polar
air masses and northern moving tropical
air masses often meet.
 At the front, the less-dense air mass is
forced to rise over the dense air mass.
 Because of this the front is usually
wedge shaped.

Guided Notes
Fronts usually bring precipitation.
 At the surface of the front the less-dense
air rises into the troposphere where the
air cools, and if humid enough, can
create clouds and bring precipitation.

Guided Notes

The weather associated with a particular
front depends on two things:
 Type of air mass
 Speed of the air mass
Guided Notes
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A cold front is the boundary
between an advancing cold
air mass and a warmer air
mass.
Cold air is denser than warm
air, so the cold air slides
underneath the warm air,
forcing it upward.
Cold air can create
thunderstorms, or just a
change in wind.
In the summer, cold fronts
can cause a decrease in
humidity
In the winter, a cold front can
cause


Rain
Snow
Guided Notes
If warm air moves cold
air, the boundary
between the air masses
is known as a warm
front.
 The advancing warm air
rises above the denser
cold air, which moves
away slowly.
 The first signs of a warm
front are high cirrus
clouds.
 Cirrus clouds may warn
of approaching
precipitation.

Guided Notes
Cold fronts usually
move twice as fast as
warm fronts.
 If a cold front “catches
up” to a warm front, the
result is an occluded
front.
 The warm air caught
between the two colder
air masses is forced
upward.
 Once the warm air rises,
it cools, often resulting
in

 Cloudiness
 Precipitation
Guided Notes

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If a front is not
moving forward, it is
a called a stationary
front.
The warmer air rises
over the denser,
colder air, and
clouds and
precipitation may
form.