1. The Atmosphere & Oceans
Global Circulation
The Atmosphere & Oceans

2. Density and Convection Currents
Convection currents in the Earth’s mantle occur because of differences in density.
Hotter, less dense material rises
Cooler, denser material sinks

3. Density and Convection Currents
Density differences also cause convection currents to form in fluids such as water and air.
The heating system in your house works because of convection currents.
Heat from a stove moves through a pot of water by convection currents.

4. Density and Convection Currents
On a global scale, density differences cause circulation of the atmosphere and the oceans.

5. Air Pressure Differences
Warm air is less dense than cold air, so it will expand and rise, which lowers air pressure.
Air will flow from areas of higher pressure to areas of lower pressure. (This is the sound you hear when you open a vaccum-packed can such as tennis balls or coffee.)

6. Air Pressure and Wind
This flow of air from high-pressure regions to low-pressure regions is what causes wind.

7. Uneven Heating of Earth’s Surface
The sun’s heat is stronger at the equator than at the poles.

8. Global Air Circulation
This uneven heating causes giant convection currents which move warm air toward the poles and cool air toward the equator.

9. Global Air Circulation on a Rotating Earth
Rotation of the Earth causes this simple convection system to break down into smaller cells.

10. The Coriolis Effect
The Coriolis Effect describes how Earth’s rotation affects moving objects.

11. The Coriolis Effect
Objects are deflected to the right in the N. Hemisphere,
To the left in the S. Hemispere
Greater deflection at the poles, no deflection at the equator

12. Ocean Currents
Ocean currents are masses of ocean water that flow from one place to another.
Surface currents are caused by friction between the ocean and the wind that blows across its surface.
Density currents are vertical currents that result from density differences among water masses.

13. Surface Currents
Huge circular-moving current systems called gyres dominate the surfaces of the oceans.
Because of the Coriolis Effect, these currents flow in opposite directions in the N. and S. Hemispheres.

14. Density Currents
In Earth’s oceans, density is based on temperature and salinity (saltiness.)
Cold water is denser than warm water.
Salt water is denser than fresh water.
Density differences account for the thorough mixing of deep-water masses.

15. The Conveyor Belt Model
Ocean circulation is like a “conveyor belt” that travels from the Atlantic Ocean through the Indian and Pacific oceans and back again.

16. Earth – A Planet on the Move
The water in the ocean, the air all around you, even the ground under your feet is in motion right now!

17. Garbage Patches