1. Air Pressure and Wind

2. What is air pressure? The force exerted by air molecules
as they collide with a surface
The weight of the atmosphere as it
pushes on Earth’s surface

3. What is air pressure? Air has mass
Gravity pulls these molecules towards Earth giving them weight
The weight of the molecules is air pressure kg

4. What is air pressure?
At sea level the weight of air pushing down is 14.7 pounds per square inch
The weight on the roof of a typical house is about 2.1 million kg (4.6 million lbs)
Why don’t all of our houses collapse?
Or Why aren’t we all squished?
CHECK THIS OUT!!!
Extreme Atmospheric Pressure

5. What is air pressure?
Air pressure is exerted (pushes) in all directions
An equal force pushing down is balanced by air pushing up

6. What Is Air Pressure? The same thing as gravity
The weight of the atmosphere pushing downward
A form of pollutant

7. Why Don’t We Get Crushed By The Pressure Of The Atmosphere?
The air is not that heavy
Air pressure is exerted in all directions, and we are in equilibrium
The water in our bodies prevents it

8. Why Did The Oil Drum Collapse?
The water weakened it
The atmosphere suddenly got heavier
The cooling vapor took up less space than before and created a drop in pressure inside. The regular air pressure then crushed the drum.

9. Measuring air pressure
The barometer is the instrument used to measure air pressure
2 types of barometers
Mercury
Aneroid
Mercury Barometer

10. Measuring air pressure
As the weight of the air increases, the mercury rises

11. Measuring air pressure
As the weight of the air decreases, the mercury lowers

12. Measuring air pressure
The Aneroid barometer
A capsule with most of the air removed changes size as the pressure outside of it increases or decreases
This moves the needle

13. Measuring air pressure
Pressure will be measured in
Mm Hg
Inches of Hg
Milibars
Average Pressure at sea level
mb = in. Hg

14. Why does air pressure change?
3 factors that affect pressure:
Elevation/Altitude (p414)
Temperature (p416)
Humidity (p416)

15. Complete the graphic organizer by filling in the 3 factors that affect pressure. Then create branches explaining how they cause pressure to change.

16. Changes in air pressure
Altitude
(height above sea level)
As the altitude increases pressure decreases
As the altitude decreases pressure increases

17. Changes in air pressure
Altitude Drawing
High Altitude / Low Pressure
Low Altitude / High Pressure

18. Changes in air pressure
Humidity
(the amount of water vapor in air)
Water molecules weigh less than O2 or N2
Water vapor replaces these molecules in humid air
As humidity increases, pressure decreases
As humidity decreases, pressure increases
HUMID AIR
DRY AIR

19. Changes in Air Pressure
Humidity Drawing
Low Humidity / High Pressure
High Humidity / Low Pressure

20. Changes in air pressure
Temperature
In warm air the molecules are far apart.
In cool air the molecules are closer together
As air temperature increases, pressure decreases
As air temperature decreases, pressure increases

21. Changes in air pressure
Temperature Drawing
High Temperature / Low Pressure
Low Temperature / High Pressure

22. Let’s Summarize Temperature Altitude Decrease Pressure Increase
Humidity

23. Low Pressure Generally associated with stormy weather.
The air is rising.

24. High Pressure
Generally associated with clear skies.
Air is sinking.

26. What does a barometer measure?
Atmospheric pressure
The humidity of the air
Air quality
How much it has rained

27. What affects air pressure?
Altitude
Humidity
Temperature
All of the above

28. Why is water vapor less dense than air?
There is less of it
H2O has less mass than O2 or N2
It is hotter, so it has less mass

29. Low pressure is usually associated with…
Sunny skies
Deserts
Earthquakes
Stormy weather and rising air

30. High pressure is usually associated with…
Rain
Tornadoes
Sunny, dry weather with sinking air
Pushy car salesmen

31. Factors Affecting Wind Direction and Speed

32. What makes the wind blow?
Air moves from
HIGH PRESSURE to LOW PRESSURE
This movement of air is WIND

33. What makes the wind blow?
Island Example

34. Factors Affecting Wind Direction
Coriolis Effect Coriolis-2.mp4
Pressure Gradients (differences in pressure HIGH vs LOW)
Friction (resistance)

35. The Coriolis Effect
An object moving over Earth’s surface will curve away from its intended path
This is due to Earth’s rotation
Faster at the equator
Slower at the poles

36. The Coriolis Effect Coriolis-1.mp4 Guidelines (p419):
objects are deflected to the RIGHT in the Northern Hemisphere and the LEFT in the Southern Hemisphere
The effect (curve) increases as the speed increases
The effect DOES NOT depend on the objects direction
The effect is greater at the poles and less at the equator
Most noticeable of large distances (Not in TOILETS)

37. The Coriolis Effect
Let’s Draw!

38. Pressure Gradients Pressure gradient:
A difference in pressure from one place to another
Remember wind blows from HIGH to LOW
The stronger the gradient the faster the wind
The faster the wind the more curve from the Coriolis Effect

39. Friction Friction between the air and the ground slows wind.
The higher above the surface the faster the wind will blow
The higher above the surface the more curve due to Coriolis

40. Friction
Little friction in the upper troposphere allows a jet stream to from moving air west to east.
The jet stream supplies energy to storms and directs the path of weather across the United States
Affects airplanes as they travel coast to coast

41. Jet Stream

42. Review Questions What are the 3 factors that affect wind direction?
What are the 3 factors that affect air pressure?
How does a pressure gradient affect the speed of wind? Direction of wind?
Why does the Coriolis Effect cause wind to deflect?
Can you witness the Coriois Effect in your bathroom?
How does friction affect wind speed?

43. What are the 3 factors that affect wind direction?
Altitude, Humidity, and Temperature
Altitude, Humidity, and Coriolis Effect
Coriolis, Pressure, Gradients, and Friction

44. What are the 3 factors that affect air pressure?
Altitude, Humidity, and Temperature
Coriolis, Pressure, Gradients, and Frction
Sunlight, Convection, and Friction

45. How does a pressure gradient affect the speed of wind?
The stronger the gradient, the weaker the wind
The stronger the gradient, the stronger the wind
It does not effect the speed

46. Why does the Coriolis Effect cause wind to deflect?
The wind was already curving; the Coriolis Effect only effects airplanes
The spinning of the Earth causes the path to curve

47. How does friction affect wind speed?
Objects or rough surfaces cause a drag on the wind
Friction makes the wind faster
Friction creates wind

48. Global and Local Winds

49. Global Winds
Global winds show the general direction the air is flowing throughout the globe.
Refer to your worksheet for these winds
The winds are named according to where the wind comes from or originates
Ex. What would the name of this wind be?

50. Global Winds Climate Zones due to global winds:
Areas of low pressure are characterized by rising air, precipitation = Rainforest (0, 60)
Areas of high pressure are characterized by sinking air, dry air = Deserts (30, 90)
** Add these areas to your worksheet

51. Continental and Local Winds
These winds can go opposite the expected global winds due to changes in local conditions:
Continental Winds
Monsoon
Local Winds
Sea breeze
Land breeze
Santa Ana Winds

52. Monsoon
A Monsoon is a seasonal change in winds.
Ex. India, North America

53. Sea Breeze: Rising Air, Sinking Air, High Pressure, Low Pressure, Dense Air, Less Dense Air, Cloud Formation

54. Land Breeze: Rising Air, Sinking Air, High Pressure, Low Pressure, Dense Air, Less Dense Air,

55. Santa Ana Winds
Occur in Southern California in the late fall/early winter
A high pressure forms as the desert regions
As the air sinks it is compressed and usually warms.

56. Santa Ana Winds
This creates an offshore wind (blows towards the ocean)
The air is very dry and often wildfires are a result of this wind

57. Where will you find areas of high pressure on Earth?
North and South Pole Only
0 and 60 Degrees Latitude
30 and 90 Degrees Latitude
Over the Ocean

58. Where will you find areas of low pressure on Earth?
North and South Pole Only
0 and 60 Degrees Latitude
30 and 90 Degrees Latitude
Over the Ocean

59. What Creates Santa Ana Winds?
High Pressure Over Land and Low Pressure Over Ocean
Low Pressure Over Land and High Pressure Over Ocean
Politicians In Santa Ana