1. Heating the Earth Air Pressure
Energy From the Sun

2. Where We Get Our Energy The Sun is a major source of energy for Earth.
You can feel the radiant energy warming your skin
Radiation- movement of energy through empty space

3. Sun’s Energy

4. Absorption of Energy
Dark surfaces absorb light, and it is usually changed into heat
Surfaces that reflect light, such as white, remain cooler

5. Conduction The troposphere is heated by moving heat through matter
How does heat move through a metal pan?
Conduction- heat moves from an area of higher temperature to area of lower temperature

6. Radiation Radiant energy travels from the Sun through space in waves
Radiation passes easily through the atmosphere to the surface
Surface radiates most back into atmosphere

7. Convection Transfer of heat within a liquid or gas
As air heats it expands, becomes lighter
Warm air becomes lighter than cool air, so warm air rises
Cooler, denser air sinks

8. Forms of Energy
Let’s look at this animation for radiation, conduction, and convection

10. What is Air Pressure? Pressure- the amount of force per unit of area
Weight- weight (force) is measured in Newtons
Ex.- Holding a book (pg. 260)
Force over small area causes more pressure than a large area

11. Air Pressure in Atmosphere
Air molecules are in constant motion and pulled toward Earth’s center by gravity
Force of all the molecules moving causes air pressure
Air pressure is greatest near surface

12. Elevation What happens to air pressure as elevation changes?
Air pressure decreases as distance above surface increases
Very little weight of air pressing down

13. Water Vapor Water evaporates from lakes, rivers, and oceans
Water vapor molecules are lighter than other gas molecules
So, more water vapor in air, the lower the air pressure

14. Measuring Air Pressure
Barometer- air pressure is measured with this instrument
Air pressure pushes down on the surface of the mercury in the containter
Standard air pressure- 760 mm of mercury or 1 atmosphere or 1, mb

15. Barometers

16. How do Winds Form?
Wind- the horizontal movement of air along Earth’s surface
Earth’s atmosphere is always in motion
Winds form as cool, heavy air moves toward warm, light air
Cool air moves along the surface toward warmer air

17. How do Winds form?
Winds are also caused by differences in air pressure
Cold, heavy air have high air pressure (Highs)
Warm, light air have low air pressure (Lows)
Speed of wind depends on the differences in air pressure

18. Air Currents Air currents- up-and-down movements of air
Some areas of Earth are warmed more than others
Warmer air expands, becomes less dense
Figure pg. 266

19. Global Winds
Winds blow from regions of high pressure to regions of low pressure
Differences in air pressure produce patters of global winds
Large wind systems that circle the Earth

20. Global Winds At the equator, warm air rises and moves toward the poles
At the poles, cool air sinks and moves toward the equator
Why do we receive cold winds during the winter in Nebraska?

21. Coriolis Effect
Winds curve as they move from high-to low-pressure regions
Winds toward equator curve to the west in the Northern Hemisphere
Winds toward poles curve to the east
Wind directions are reversed in Southern Hemisphere

22. Coriolis Effect

23. Trade Winds Prevailing pattern of easterly winds
Found mainly in the tropics
Responsible for steering tropical storms in the southern hemisphere

24. Prevailing Westerlies
Blow strongest between degrees latitude
Felt strongest during winter seasons
Blow from west to east
Responsible for steering cyclones

25. Polar Easterlies Cold, dry winds that blow at high latitudes
Blow from east to west
Often weak and irregular winds

26. Sea and Land Breezes
All winds are caused by temperature differences and changes in air pressure
Breeze coming from the sea toward the land is a sea breeze
Breeze coming from the land toward the sea is a land breeze

27. Sea Breeze
During the day, air over land is warmer and lighter than air over water
The cooler, heavier air over the ocean moves in toward the land
The result is a sea breeze

28. Sea Breeze

29. Land Breeze At night, land cools faster than water
Air over land becomes cooler than the air
Heavier air over the land moves toward the water
Warmer, lighter air rises over the land

30. Land Breeze