Basic Properties of the Atmosphere

1
Basic Properties of the Atmosphere
2
Essential Points

1. Heat, Temperature and Temperature Scales
2. The Electromagnetic Spectrum
3. Composition of the Atmosphere
4. Layers in the atmosphere are defined by
   temperature profiles
5. How pressure varies in the atmosphere
6. Principal weather instruments
7. Earths radiation budget

3
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

4
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
  youll get burned. Same temperature, much larger
  amount of heat.

5
Heat and Temperature

• The earths 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.

6
Temperature Scales

• Fahrenheit
• 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

7
Converting C to F In Your Head

• Double the Centigrade
• Subtract the first Digit
• Add 32

8
Converting F to C In Your Head

• Subtract 32
• Add the first Digit
• Divide by two

9
Absolute Temperature

• Once atoms stop moving, thats 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

10
Electromagnetic Radiation

• Radio cm to km wavelength
• Microwaves 0.1 mm to cm
• Infrared 0.001 to 0.1 mm
• Visible light 0.0004 0.0007 mm
• Ultraviolet 10-9 4 x 10-7 m
• X-rays 10-13 10-9 m
• Gamma Rays 10-15 10-11 m

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Composition of the Atmosphere

• Nitrogen 78.08
• Oxygen 20.95
• Argon 0.93 (9300 ppm)
• Carbon Dioxide 0.035 (350 ppm)
• Neon 18 ppm
• Helium 5.2 ppm
• Methane 1.4 ppm
• Ozone 0.07 ppm

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Other Components of the Atmosphere

• Water Droplets
• Ice Crystals
• Sulfuric Acid Aerosols
• Volcanic Ash
• Windblown Dust
• Sea Salt
• Human Pollutants

13
Structure of the Atmosphere

• Defined by Temperature Profiles
• Troposphere
• Where Weather Happens
• Stratosphere
• Ozone Layer
• Mesosphere
• Thermosphere
• Ionosphere

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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

15
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

16
Mesosphere

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

17
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

18
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

19
Air Pressure

• By lucky coincidence, earths 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

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Pressure and Altitude

• Average at sea level 1013 mb
• 500 mb at 5 km (upper limit of permanent human
  settlement)
• 280 mb at 10 km
• 56 mb at 20 km
• 1 mb at 50 km
• 0.00056 mb at 100 km
• Roughly drops by half each 5 km of altitude

21
Pressure and Altitude
22
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

23
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

24
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

25
Atmospheric Measurements

• Temperature
• Pressure
• Humidity
• Wind Velocity and Direction

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Weather Instruments

• Temperature Thermometer
• Pressure Barometer
• Humidity Hygrometer
• Wind Velocity and Direction
• Anemometer and Wind Vane

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Thermometers

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

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Barometers

• Mercury
• 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

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Hygrometers

• Filament
• 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

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Sounding

• Balloons carry radiosondes
• Thermometer
• Barometer
• Hygrometer
• Transmitter
• Typically reach 30 km before balloon breaks

31
Radar

• Detect precipitation types and amounts
• Doppler radar measures velocity of winds

32
Satellite Studies

• Visual imagery
• Infrared imagery
• Laser spectroscopy

33
Earths Radiation Budget

• What comes in must go out
• Direct Reflectance (Short Wave)
• 31
• Infrared Re-emission (Long Wave)
• 69

34
How Heat Moves

• Radiation
• Conduction
• Convection

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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
• Ocean 3 5
• Camera light meters set to 18

36
Global Albedo