Download Global Wind Patterns

Global Wind Patterns
Global Wind Belts & the Jet Stream
Air Basics
• Air is a substance that surrounds us, takes up space, and
whose movement we feel as wind.
• Weather and climate involve the transfer of energy in and
out of the atmosphere.
• Solar radiation heats the land masses, oceans, and air.
• Wind is the result of horizontal differences in air pressure.
• Wind direction is given as the direction from which the
wind comes. (example, a "north wind" blows from north to south)
• When the difference in pressure between two areas is small, the wind may move too
slowly to be noticeable.
•A very large pressure difference can produce wind strong enough to uproot trees.
Global Winds
• Different parts of the world
receive different amounts of heat
from the sun.
• Uneven heating between the
equator and the north and south
poles causes global winds.
• Colder air from the poles tends to
sink and move towards the
equator closer to the surface of
the Earth.
• Warm air from the equator rises
and moves towards the poles high
in the atmosphere because it is
lighter.
Earth’s Rotation affects Wind Direction
• If the Earth did
not rotate,
global winds
would flow
directly from the
poles to the
equator.
Earth’s Rotation affects Wind Direction
• Earth’s rotation
changes the
direction of winds
and other objects
moving over Earth.
• The influence of
Earth’s rotation on
wind or other
moving objects is
called the Coriolis
Effect.
Earth’s Rotation affects Wind Direction
• Global winds curve as
Earth turns beneath
them. In the
• Northern
Hemisphere, winds
curve to the right in
the direction of
motion.
• Winds in the
Southern
Hemisphere curve to
the left.
• The Coriolis effect is
noticeable only for
winds that travel long
distances.
Earth’s Rotation affects Wind Direction
• Because the Coriolis
effect causes global
winds to curve, they
cannot flow directly
from the poles to
the equator.
• Instead, global
winds travel along
three routes in each
hemisphere.
• These routes, which
circle the world, are
called global wind
belts.
Coriolis Effect
Click on image to see animation of the Coriolis effect
Global Winds Animated
Global Winds
• Global winds
travel
thousands of
kilometers in
steady patterns;
global winds
last for weeks.
Global Winds
Polar easterlies
Prevailing westerlies
Tropical easterlies
(Trade winds)
Equator
Tropical easterlies
(Trade Winds)
Prevailing westerlies
Polar easterlies
Jet Stream
• The jet streams are narrow belts of high speed
winds that blow in the upper troposphere and
lower stratosphere
• Separate warm air from cold air
Jet Stream
• Jet Streams usually flow in the upper troposphere from west to east for
thousands of kilometers.
• Air often moves in Jet streams at speeds greater than 200 kilometers
per hour (124 mph).
• Jet streams form because of the uneven heating of the Earth’s surface.
• Instead of following a straight line, jet streams loop north and south.
Jet Stream
• Each hemisphere usually has two jet streams, a polar jet stream and a
subtropical jet stream.
• The polar jet streams flow closer to the poles in summer than in winter.
• The polar jet stream has a strong influence on weather in North America. It can
pull cold air down from Canada into the United States and pull warm air up
toward Canada.
• Strong storms tend to form along its loops. Scientists must know where the jet
stream is flowing to make accurate weather predictions.
The Jet Stream
Local Winds
Sea Breezes
• Occur on warm sunny days
• Air over the land heats faster than the
air over the cool ocean
•Warmer air rises
•Cool air flows in under it to fill the area
over the land
•This air warms and the cycle continues
Changes in Pressure
•Air flows from high air pressure area
toward a low pressure area
•High pressure usually brings clear
weather
•Low pressure usually brings stormy
weather
Land Breezes
•Occur at night and on cool days
•Air over water maintains an even
temperature
•Air over land cools faster
•Cooler air flows from the land out under
the warmer ocean air
•This air warms and the cycle continues
Changes in Temperature
•As air is heated by the sun, it begins to
rise
•Cool air flows in under it and takes it's
place
•This cycle is repeated continuously
If you know the temperature and pressure in different areas, you
will always be able to predict the wind direction.
Click on diagram to see the animation of Land and Sea Breezes
Green House Effect
Select picture for animation
Coriolis Effect
Select picture for animation