1. What Causes Wind?

2. Solar Energy
Radiation – Energy that travels over distances in the form of certain types of waves.
Conduction – The transfer of heat energy from one substance to another through direct contact.
Convection – The transfer of energy from place to place by the motion of gas or liquid.

3. 1. Solar radiation heats the surface. 2
1. Solar radiation heats the surface. 2. The surface conducts energy to air. 3. Warm, less dense air rises by convection.
Transfer of Energy
Radiation, conduction, and convection move energy from place to place.

4. Solar Energy
Some places on Earth’s surface absorb more energy than other places – land vs. water, equator vs. poles.
These places become hotter and cause more convection, rising air.
Uneven heating of Earth’s surface causes air to rise in some places and sink in others.

5. AIR PRESSURE The force of air molecules pushing on an area.
Air molecules move in all directions, air pressure pushes in all directions.

6. How does UNEVEN HEATING of Earth’s surface cause air pressure differences?
High Air Pressure areas are a result of cooler, denser, sinking air.
Example – North and South Pole
Low Air Pressure areas are a result of warmer, less dense, rising air.
Example - Equator

7. Wind The Sun heats The Earth unevenly.
Areas of High and Low Pressure form.
Air moves horizontally across the surface from areas of HIGH PRESSURE to areas of LOW PRESSURE.

8. Wind

9. Global Winds
Because of the shape of Earth, the equator receives more direct radiation than the poles.
Convection of warm, rising air at the equator causes a LOW PRESSURE area.
Cool, sinking air at the poles causes a HIGH PRESSURE area.
Global Wind Simulation

10. Coriolis Effect
Global Winds flow from the poles toward the equator, but curve due to the Coriolis Effect.

11. Jet Streams
Jet Streams are winds that travel long distances (thousands of kilometers) in the upper troposphere.
Caused by uneven heating of Earth’s surface.
2 Subtropical and 2 Polar Jet Streams
Polar Jet Stream affects weather in North America.