1. Basic Properties of the Atmosphere

2. Heat and Temperature
Temperature: Average energy of molecules or atoms in a material
Heat: Total energy of molecules or atoms in a material
Can have large amount of heat but low temperatures
Can have high temperatures but little heat

3. Heat and Temperature
The Arctic Ocean has a large amount of heat (because of large mass) even though the temperature is low.
Air in an oven at 500 F has high temperature but little heat.
However, touch anything solid in the oven, and you’ll get burned. Same temperature, much larger amount of heat.

4. Heat and Temperature
The earth’s outermost atmosphere is extremely “hot” but its heat content is negligible
The surface of the moon can reach 250 F in sunlight and -200 F in shadow, but the vacuum around the Apollo astronauts contained no heat.
It takes time for things to warm up and cool off.

5. Temperature Scales Fahrenheit Centigrade or Celsius
Water Freezes at 32 F
Water Boils at 212 F
Centigrade or Celsius
Water Freezes at 0 C
Water Boils at 100 C
Two scales exactly equal at -40

6. Converting C to F – In Your Head
Double the Centigrade
Subtract the first Digit
Add 32

7. Converting F to C – In Your Head
Subtract 32
Add the first Digit
Divide by two

8. Absolute Temperature
Once atoms stop moving, that’s as cold as it can get
Absolute Zero = -273 C = -459 F
Kelvin scale uses Celsius degrees and starts at absolute zero
Most formulas involving temperature use the Kelvin Scale

9. Electromagnetic Radiation
Radio: cm to km wavelength
Microwaves: 0.1 mm to cm
Infrared: to 0.1 mm
Visible light – mm
Ultraviolet 10-9 – 4 x 10-7 m
X-rays – 10-9 m
Gamma Rays –10-11 m

10. Composition of the Atmosphere
Nitrogen %
Oxygen %
Argon 0.93% (9300 ppm)
Carbon Dioxide % (350 ppm)
Neon 18 ppm
Helium 5.2 ppm
Methane 1.4 ppm
Ozone ppm

11. Other Components of the Atmosphere
Water Droplets
Ice Crystals
Sulfuric Acid Aerosols
Volcanic Ash
Windblown Dust
Sea Salt
Human Pollutants

12. Structure of the Atmosphere
Defined by Temperature Profiles
Troposphere
Where Weather Happens
Stratosphere
Ozone Layer
Mesosphere
Thermosphere
Ionosphere

13. Troposphere Heating of the Surface creates warm air at surface
Warm air rises, but air expands as it rises and cools as it expands (Adiabatic cooling)
Heating + Adiabatic Cooling = Warm air at surface, cooler air above
Buoyancy = Cool air at surface, warmer air above
Two opposing tendencies = constant turnover

14. Stratosphere Altitude 11-50 km Temperature increases with altitude
-60 C at base to 0 C at top
Reason: absorption of solar energy to make ozone at upper levels (ozone layer)
Ozone (O3) is effective at absorbing solar ultraviolet radiation

15. Mesosphere 50 – 80 km altitude Temperature decreases with altitude
0 C at base, -95 C at top
Top is coldest region of atmosphere

16. Thermosphere 80 km and above
Temperature increases with altitude as atoms accelerated by solar radiation
-95 C at base to 100 C at 120 km
Heat content negligible
Traces of atmosphere to 1000 km
Formerly called Ionosphere

17. Why is the Mesosphere so Cold?
Stratosphere warmed because of ozone layer
Thermosphere warmed by atoms being accelerated by sunlight
Mesosphere is sandwiched between two warmer layers

18. Composition and Altitude
Up to about 80 km, atmospheric composition is uniform (troposphere, stratosphere, mesosphere)
This zone is called the homosphere
Above 80 km light atoms rise
This zone is sometimes called the heterosphere

19. Mean Free Path
Below 80 km, an atom accelerated by solar radiation will very soon hit another atom
Energy gets evenly distributed
Above 80 km atoms rarely hit other atoms
Light atoms get accelerated more and fly higher
Few atoms escape entirely

20. Planets and Atmospheres
At top of atmosphere, an atom behaves like any ballistic object
Velocity increases with temperature
If velocity exceeds escape velocity, atom or molecule escapes
Earth escape velocity 11 km/sec.
Moon escape velocity 2.4 km/sec

21. Atmospheric Measurements
Temperature
Pressure
Humidity
Wind Velocity and Direction

22. Weather Instruments Temperature: Thermometer Pressure: Barometer
Humidity: Hygrometer
Wind Velocity and Direction:
Anemometer and Wind Vane

23. Thermometers Fluid Bimetallic Electronic Mercury Alcohol
Use expansion of fluid
Bimetallic
Differential expansion of different metals
Electronic
Electrical resistance change with temperature

24. Barometers Mercury Aneroid
Air pressure will support 10 meters of water
Mercury is 13 times denser
Air pressure will support 76 cm of mercury
Aneroid
Air pressure deforms an evacuated chamber

25. Hygrometers Filament Sling Psychrometer Electrical
Hair expands and contracts with humidity
Sling Psychrometer
Measures cooling by evaporation
Two thermometers
Wet bulb and Dry bulb
Electrical
Chemicals change resistance as they absorb moisture

26. Sounding Balloons carry radiosondes
Thermometer
Barometer
Hygrometer
Transmitter
Typically reach 30 km before balloon breaks

27. Radar Detect precipitation types and amounts
Doppler radar measures velocity of winds

28. Satellite Studies
Visual imagery
Infrared imagery
Laser spectroscopy

29. Earth’s Radiation Budget
What comes in must go out
Direct Reflectance (Short Wave)
31%
Infrared Re-emission (Long Wave)
69%

30. How Heat Moves
Radiation
Conduction
Convection

31. Albedo Albedo = % incident energy reflected by a body
Fresh snow: 75 – 95%
Old snow: 40 – 60%
Desert: 25 – 30%
Deciduous forest, grassland: 15 – 20%
Conifer forest: 5 – 15%
Camera light meters set to 18%

32. Global Albedo

33. Air Pressure
By lucky coincidence, earth’s atmospheric pressure is approximately neat round numbers in metric terms
14.7 pounds per square inch (1 kg/cm2)
Pressure of ten meters of water
Approximately one bar or 100 kPa
Weather reports use millibars (mb)
One mb = pressure of one cm water

34. Pressure and Altitude Average at sea level 1013 mb
500 mb at 5 km (upper limit of human settlement)
280 mb at 10 km
56 mb at 20 km
1 mb at 50 km
mb at 100 km

35. Pressure and Altitude