1. Properties of the Atmosphere
Unit #6
Properties of the Atmosphere

2. Vocabulary Weather Meteorology Atmosphere
The short-term conditions of the atmosphere
Meteorology
The study of the atmosphere and its properties
Atmosphere
Blanket of gas that surrounds the Earth

3. Gas of the atmosphere Earth Science Reference Table page 11 Nitrogen
Oxygen
Carbon dioxide
Water Vapor
Methane

5. Structure of the Atmosphere
ESRT page 14
Decreases
0 km
Stratosphere and thermosphere
Troposphere
Greenhouse gases

7. Air Pressure
à  Caused by the weight of the air molecules in the atmosphere
à  The atmosphere extends kilometers above the Earth’s surface
à  The weight of the air exerts a pressure of nearly 15 lbs/in2
à  The air pressure is greatest at the surface and decreases with altitude
 Since, the pressure is exerted in every direction we are seldom aware of it.

8. Air pressure is seen when:
1) Drinking through a straw

9. Effects of air pressure Macro-scale

10. Measuring Air Pressure
Air pressure can be measured with a barometer.
Two types of barometers:
1) Mercury barometer
uses mercury in a column an measures the change in air pressure

11. 2) Aneroid Barometer
 air pressure causes changes to the metal cover on a air tight box, which is translated to an dial.

12. Air pressure is measured in:
Millibars
Inches of mercury
Convert pressures by reading across the scale
mb = inches of Hg

13. Points of equal pressure are connected by isobars.
Isobars – connect points of equal pressure

14. How does air pressure affect us?
1) Airplane travel many kilometers above the surface, since the air is very thin, the cabins are pressurized
2) Mountaineers often take along oxygen on very high mountains because the air is thin at high elevations

15. Factors affecting Atmospheric Pressure
1) Temperature
à When air cools it contracts and becomes more dense, increasing pressure.
à When air is heated it expands and becomes less dense, decreasing pressure.
à This is an inverse relationship.

16. Factors affecting Atmospheric Pressure
2) Moisture
à Water has a mass of 18 AMU
à Nitrogen has a mass of 28 AMU
 If there is more moisture (water) in the air, the air will be lighter and decrease the pressure.

17. Moisture in the Atmosphere
 Water Vapor: water in the gas form
 Air has the ability to hold to hold water vapor
 Think of air as a container, which can only hold a limited amount of moisture.

18. Unsaturated
Saturated

19. Unsaturated vs. Saturated
Unsaturated Air: air that is not holding as much water vapor as possible
Saturated Air: air that is holding as much water vapor as possible
à water vapor will start to condensate to form droplets of water
Water vapor can not be seen, water droplets can be seen (clouds)

20. Ways to make air saturated:
1) Add more water vapor to the air
2) Lower the temperature of the air
à  lowering temperature air has a reduced ability to hold moisture
60 deg. F unsaturated
40 deg. F
saturated

21. Dew point
The temperature to which the air must be cooled to become saturated, condensation will occur

22. Measuring Moisture in the Atmosphere
 Moisture is determined by measuring the amount of evaporation.
Evaporation causes cooler temperatures.
Lower temperature, due to evaporation
Measures the air temperature, Higher temperature

23. The amount of moisture is determined by measuring the difference in temperature caused by evaporation and the air temperature.
Psychrometer  tool used to measure the air temperature and the temperature after evaporation.

24. Relative Humidity
à expresses the amount of moisture in the air, compared to how much it can hold.
50% Humidity
25% Humidity

25. Influences of humidity:
à High humidity can make the air uncomfortable
    When the relative humidity is 100%, the dew point is reached and condensation occurs

28. Wind
à Movement of air due to convection currents, temperature and densities changes
 Uneven heating of the Earth causes differences in air pressure
Wind moves from areas of high pressure to areas of low pressure
Anemometer  tool used to measure wind speed

29. Determining Wind Strength
Winds strength is determined by the pressure gradient
Pressure gradient  change in pressure over a distance
à larger gradient =
stronger winds
à smaller gradient =
slower winds

30. Sea Breeze
Low Pressure
High Pressure

31. Land Breeze
High Pressure
Low Pressure

32. Land heats and cools faster than water creating Low pressure during the day
Water heats and cools slower, creating low pressure at night

33. Prevailing Winds and Ocean Currents
Notice how both the maps generally match.
Winds are the major factor in moving the surface waters of the oceans.
Winds are moving between areas of high and low pressure, but notice:
The winds follow a curved path this is due to the Coriolis Effect

34. Coriolis Effect: (song)
Due to the Earth’s rotation, freely moving object like wind and water, will follow a curved path,
à  curving to the right in the Northern Hemisphere
à curving to the left in the Southern Hemisphere

35. Large Scale

36. Small Scale
Rotate Counter clockwise
Rotate Clockwise

39. When air moves from High to Low pressure wind is created. (song)
Vertical Movement
Rising
Sinking
Horizontal Movement
Into the center
Out of the center
Cause
Less dense are rising
More dense air sinking
Effect
Cooling, condensation and cloud formation
Warming, drying clear skies
Also known as
Convergence Zone
Divergence Zone

40. High and Low Pressure

41. Where will clouds form? Formation of clouds requires:
Water vapor
Lower temperatures
Condensation nuclei
Clouds form when water vapor condensates
As air rises, the temperature decreases due to expansion and lower pressures
Condensation nuclei  tiny dust particles suspended in the air on which condensation can occur.
Air rises, cools & condensates within a Low pressure system
When the air temperature cools to the dew point, condensation will occur and a cloud will form

42. If air temperature and dew point are not the same at the surface, how can they cool to the same temperature in the troposphere?
The air temperature will cool faster than the dew point temperature

43. Cloud height chart
Use the air temperature & dew point

44. Temperature is 30 C and the dew point is 20 C, what is the cloud height?

45. How do clouds form and cause precipitation?
Clouds form when rising air is cooled below its dew point.
 As air rises, the air cools due to expansion and condensation occurs.
Condensation nuclei tiny particles of dust upon which condensation will occur.
Rain Drops get larger as smaller drops of water bump into each other.
Clouds  mass of liquid water droplets suspended in air.
Precipitation  water fall from the sky

46. Large cloud droplet
drizzle droplet
Cloud droplet
Condensation nuclei
Large rain drop

47. Types of Precipitation
Type of Precipitation
Description
Rain
Water droplets falling from the sky
Snow
Frozen water crystals
Sleet
Partially frozen mixture of rain and snow
Hail
Ice balls created from repeated freezing and thawing

48. Temperature and Atmospheric Pressure
 As temperature increases, the pressure will decrease because the air is less dense.
 As the temperature decreases the pressure will increase because the air is more dense.
 Inverse relationship

49. Temperature and Relative Humidity
 As the temperature increases the relative humidity will decrease because the air has a greater ability to hold moisture.
 As the temperature decreases the relative humidity will increase because the air has a lower ability to hold moisture.
 Inverse relationship