1. Global Wind Belts & the Jet Stream
Global Wind Patterns
Global Wind Belts & the Jet Stream

2. 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)

3. 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.

4. 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.

5. Earth’s Rotation affects Wind Direction
If the Earth did not rotate, global winds would flow directly from the poles to the equator.

6. 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.

7. 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.

8. 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.

9. Coriolis Effect
Click on image to see animation of the Coriolis effect

10. Global Winds Animated

11. Global Winds
Global winds travel thousands of kilometers in steady patterns; global winds last for weeks.

12. Global Winds Polar easterlies Prevailing westerlies
Tropical easterlies
(Trade winds)
Equator
(Trade Winds)

13. 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

14. 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.

15. 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.

16. The Jet Stream

17. Changes in Temperature
Local Winds
Sea Breezes
Land 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
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
Changes in Pressure
Changes in Temperature
Air flows from high air pressure area toward a low pressure area
High pressure usually brings clear weather
Low pressure usually brings stormy weather
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.

18. Click on diagram to see the animation of Land and Sea Breezes

19. Green House Effect
Select picture for animation

20. Coriolis Effect
Select picture for animation