1. Convection in Our Atmosphere
Credit to:
Burnett Middle School
8th Grade Science

2. Previous Knowledge
What do you already know about convection?

3. CONVECTION
is the transfer of heat by the movement of warmed matter (air or liquid)

4. The Sun provides the energy that drives convection within the atmosphere and oceans, producing winds and ocean currents.

5. Hot Air is Less Dense!

6. What is most dense SINKS!
Atmospheric Density
What is most dense SINKS!

7. CONVECTION

8. CONVECTION

9. CONVECTION CURRENTS move the air in our atmosphere!
We have global winds that blow because of these large convection currents

10. CONVECTION
Wind over the shore changes direction because of EARTH’S UNEVEN WARMING & COOLING! We can these local winds

11. Click the Video button to watch a movie about convection currents.

12. CONVECTION DEMOS! Tea bag http://www.youtube.com/watch?v=G9QJ1vv2WyM
Colored Water

13. Why does hot air rise and cold air sink?
Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.
Why are the heating elements placed beneath hot water tanks in people’s homes?
Hot water rises.
So when the element heats the water, and the hot water rises, the water tank is filled with hot water.

14. Wind

15. Wind is the movement of air from an area of high pressure to an area of low pressure.
This is caused by the unequal heating of the Earth’s surface.
As air is heated, it becomes less dense and rises. The air pressure is also lower .
Cooler, more dense air, has a higher pressure, and moves under the warmer air.
This causes a convection current,
creating wind
The greater the pressure
difference, the faster the air
moves, and the stronger the
wind blows.

16. How is Wind Measured?
Wind direction is measured with a wind vane, which points in the direction the wind is coming from.
This is how the wind is named.
A western wind is blowing from the west.
This means a northern wind actually blows toward the south.
Wind speed is measured with an instrument called an anemometer.

17. Why We have Global Winds
Since the air near the equator is less dense, it rises forming areas of low pressure.
The cold air near the poles sinks because it is more dense, forming areas of high pressure.
The air moves in large circular patterns called convection currents.
The change in density is due to the unequal heating of Earth’s
surface

18. L H 90 30 60 Cold Moist Air Rises Cool Dry Air Sinks60 90
Warm Moist Air Rises
Very Cold Air Sinks
Cold Moist Air Rises
Cool Dry Air Sinks
Cool Dry Air Sinks
Cold Moist Air Rises
Very Cold Air Sinks

19. Wind Moves from HIGH to LOW30 60 90
Wind Moves from HIGH to LOW

20. Objects are deflected to the RIGHT in the Northern Hemisphere30 60 90
Objects are deflected to the
RIGHT in the Northern Hemisphere
But why?

21. The Coriolis Effect
As Earth rotates, the Coriolis effect turns winds in the Northern Hemisphere toward the right.

22. Northern Global Wind Patterns
Polar Easterlies
90 – 60 latitude from the east
Prevailing Westerlies
60 – 30 latitude from the west
Trade winds
30 – 0 latitude from the East

23. Global Winds
Polar Easterlies are the wind belts that extend from the poles to 60° latitude in both hemispheres. They form as cold, sinking air moves away from the poles. They can carry cold arctic air over the U.S. which can produce snow and freezing weather.
Westerlies are the wind belts found between 30° and 60° latitude in both hemispheres. They blow toward the poles from west to east. These winds can carry moist air of the U.S. producing rain and snow.
Trade Winds are the winds that blow from 30° latitude almost to the equator in both hemispheres. They curve to the West as they blow toward the equator.

24. Global Winds, continued
The Doldrums The trade winds of the Northern and Southern Hemispheres meet in an area around the equator called the doldrums. there is very little wind because the warm, rising air creates an area of low pressure. The name doldrums means “dull” or “sluggish.”

25. Global Winds
Sailing the global winds activity

26. Jet Streams
Narrow belts of high-speed winds that blow in the upper troposphere and lower stratosphere. Knowing the path of a jet stream is important not only to pilots but also to meteorologists. Because jet streams affect the movement of storms, meteorologists can track a storm if they know the location of a jet stream.

27. Jet Streams
Jet Streams form at latitudes where wind systems come together
High speed westerly winds form high above the surface

28. Local Winds Sea Breeze Land Breeze
Local winds move over a short distance
Caused by the heating of a small area of Earth’s surface
Sea Breeze
The sun warms the land faster than the water, so the air above
the land becomes warmer.
The cooler air over the water moves inland
Land Breeze
At night, the land cools faster than the water, so the air above
the land becomes cooler.
The cooler air over the land moves out to the water.

29. Local Winds
Local winds generally move short distances and can blow from any direction.
Mountain and valley breezes are examples of local winds caused by an area’s geography.
Sea and land breezes are affected by temperature.

31. Air Currents
United streaming video – 11 minutes