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Air Masses, Global Winds,
and Fronts
Meteorology, Weather and Climate
Meteorology is the study of atmospheric
phenomena. Meteorology includes weather
and climate.
• Weather is the short-term variations in
atmospheric phenomena that interact and
interfere with the environment and life.
• Climate is the long-term variations of
weather in a certain area.
Air Masses
An air mass is a large volume of air that has
the same characteristics, such as humidity
and temperature, as its source region.
A source region is the area over which an
air mass forms.
Source Regions
Tropical
 Polar
 Arctic
 Continental
 Maritime
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Global Wind Systems
The directions of Earth’s winds are
influenced by Earth’s rotation.
This Coriolis effect results in fluids and
objects moving in an apparent curved path
rather than a straight line.
http://www.youtube.com/watch?v=iCvaW
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Global Wind Systems
The directions of
Earth’s wind systems,
such as the polar
easterlies and the
trade winds, vary
with the latitudes in
which they occur.
Global Wind Systems
Polar easterlies
The polar easterlies are the wind zones between
60 N latitude and the north pole, and 60 S
latitude and the south pole.
Prevailing westerlies
The prevailing westerlies are the wind
systems on Earth located between latitudes
30 N and 60 N, and 30 S and 60 S.
Global Wind Systems
Trade winds
Between latitudes 30 N and 30 S are two
circulation belts of wind known as the trade
winds.
Near latitudes 30 N and 30 S, the sinking air
associated with the trade winds creates an area
of high pressure. This results in a belt of weak
surface winds called the horse latitudes.
Global Wind Systems
Trade winds
Trade winds from the North and the South meet
and join near the equator. The air is forced
upward, which creates an area of low pressure.
This process, called convergence, can occur on
a small or large scale. Near the equator, it
occurs over a large area called the
intertropical convergence zone (ITCZ).
Global Wind Systems
Global Wind Systems
Jet Streams
A jet stream is a narrow
band of fast, highaltitude, westerly wind.
Weather in the middle
latitudes is strongly
influenced by fastmoving, high-altitude jet
streams.
Jet Streams
Types of jet streams
The major jet streams, called the polar jet streams,
separate the polar easterlies from the prevailing
westerlies.
The minor jet streams are the subtropical jet
streams. They occur where the trade winds meet the
prevailing westerlies.
Fronts
There are four types of fronts:
 Cold Front
 Warm Front
 Stationary Front
 Occluded Front
Cold Fronts
Cold Fronts occur when cold, dense air
displaces warm, less dense air forcing it up along
a steep slope. This collision results in intense
precipitation and sometimes thunderstorms.
Warm Fronts
Warm fronts occur when advancing warm air
displaces cold air developing a gradual boundary
slope. Often causes widespread light
precipitation.
Stationary Fronts
Stationary Fronts occur when two air masses
meet but neither advances resulting in light
winds and precipitation.
Occluded Fronts
Occluded fronts occur when a cold air mass
moves so rapidly that it overtakes a warm front
forcing the warm air upward. Strong winds and
heavy precipitation are common along an
occluded front.
Cold Front
Warm Front
Occluded Front
Stationary Front
Pressure Systems
In the northern hemisphere, winds move
counterclockwise around a low-pressure
center, and clockwise around a highpressure center.
Low-pressure center
High-pressure center
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Pulling it all together:
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http://www.youtube.com/watch?v=LD4hSW2
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