Basic Properties of the Atmosphere

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

4
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.

5
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

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, 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

9
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

10
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

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

24
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

25
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

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
Earths 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, 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

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
• 0.00056 mb at 100 km

35
Pressure and Altitude