Download SOURCE REGIONS - WHERE AIR MASSES ACQUIRE THEIR

What is an Air Mass?
 Air masses are large bodies of air which have
similar temperature and moisture
characteristics.
 Air masses form when air stays over a region
(called the source region) for several days.
 Air masses that form over water will be moist,
called MARITIME air masses
 Air masses that form over land will be dry,
called CONTINENTAL air masses
Air Masses
 An air mass that forms over a cold portion
of the Earth is called a POLAR air mass.
 An air mass that forms over a warm portion
of the Earth is called a TROPICAL air mass.
 An air mass that forms over an
extraordinarily cold portion of the Earth is
called an ARCTIC air mass.
SOURCE REGIONS - WHERE
AIR MASSES ACQUIRE THEIR
PROPERTIES
Air Masses are Classified According to:
Surface of source region
Continental (c) Forms over land - dry
Maritime (m) Forms over ocean - moist
Temperatures
Tropical (T) -Low latitudes - warm
Polar (P) - High latitudes - cold
Arctic (A) - Poles - very cold and dry
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cT
cP
mT
mP
Continental Tropical – dry & warm
Continental Polar – dry & cold
Maritime Tropical – humid & warm
Maritime Polar – humid & cold
 cA Continental Arctic – very dry & very
cold
NORTH AMERICAN AIR MASS
SOURCE REGIONS
 The general movement of the four main types of air
masses that influence the weather over the United
States. The tropical air masses visit most often in the
summer, and the polar air masses visit most often
during the winter. During other times, the polar and
tropical air masses battle back and forth over the land.
 Storm tracks across the continental United States
From West to East. This makes it possible to predict
What weather is coming our way.
FRONTS
 Fronts are boundaries that separate air
masses
 There are four types of front:
– Stationary front
– Cold front
– Warm front
– Occluded front
Go to page 13 of your ESRT!
Fronts – boundary that separates 2
different air masses
 Either a warm front is advancing or a cold
front is advancing.
COLD FRONT
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Cold air replaces warm
Much steeper than warm fronts
Advances faster than warm front
More violent weather -cumulonimbus clouds
Short, sharp showers
Cold Front
 A cold front occurs when a more dense air mass
pushes under a less dense air mass – short–
lived thunderstorms
WARM FRONT
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Warm air replaces cold
Gentle slope
Covers a wide area with its weather
Stratus clouds get lower as front
approaches
 Drizzle or steady rain
Warm Front
 A warm front occurs when a less dense air
mass rides up over a more dense air mass –
longer, steady precipitation
STATIONARY FRONTS
 Cold and warm air masses next to each
other
 Neither air mass advances
Stationary Front
 A stationary front occurs when the air masses
on either side of the front are not moving
toward each other.
OCCLUDED FRONTS
 Cold front overtakes the cool front
 Lifts the warm air off the ground
 Clouds and rain possible
Occluded Front
Air rising and cooling to the dew point by expansion (adiabatic
cooling)
By forced lifting—such as when less dense warm air is forced
above more dense cold air (when two air masses meet)
Kinds of Fronts
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Cold Fronts
Warm Fronts
Stationary Fronts
Occluded Fronts
A continental polar air mass comes down
from Canada and meets a maritime
tropical air mass from the Gulf of Mexico.
Watch the cloulds form.
Air rising and cooling to the dew point by expansion (adiabatic
cooling)
By convection: The Sun heating the ground (by radiation), which then
heats the air above (by conduction), which then rises due to convection (is
less dense than the cooler air surrounding it.)
Picture from the National Audubon Society Field Guide to Weather
Air will rise when it
is heated, because it
will become less
dense. Air moves
in to replace the air
that rose up. The
converging air will
further rise. As it
rises, it cools and
water vapor will
condense. This will
release latent heat,
and further heat
the column of air.