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.Earth’s 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 1. Heat, Temperature and Temperature Scales

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 you’ll get burned. Same temperature, much larger amount of heat. 1. Heat, Temperature and Temperature Scales

5. 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. 1. Heat, Temperature and Temperature Scales

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 1. Heat, Temperature and Temperature Scales

7. Converting C to F – In Your Head Double the Centigrade Subtract the first Digit Add 32 1. Heat, Temperature and Temperature Scales

8. Converting F to C – In Your Head Subtract 32 Add the first Digit Divide by two 1. Heat, Temperature and Temperature Scales

9. 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 1. Heat, Temperature and Temperature Scales

10. Electromagnetic Radiation Radio:cm to km wavelength Microwaves:0.1 mm to cm Infrared:0.001 to 0.1 mm Visible light0.0004 – 0.0007 mm Ultraviolet10 -9 – 4 x 10 -7 m X-rays10 -13 – 10 -9 m Gamma Rays10 -15 –10 -11 m 2. The Electromagnetic Spectrum

11. Composition of the Atmosphere Nitrogen 78.08% Oxygen 20.95% Argon0.93% (9300 ppm) Carbon Dioxide 0.035%(350 ppm) Neon18 ppm Helium5.2 ppm Methane1.4 ppm Ozone0.07 ppm 3. Composition of the Atmosphere

12. Other Components of the Atmosphere Water Droplets Ice Crystals Sulfuric Acid Aerosols Volcanic Ash Windblown Dust Sea Salt Human Pollutants 3. Composition of the Atmosphere

13. Structure of the Atmosphere Defined by Temperature Profiles Troposphere –Where Weather Happens Stratosphere –Ozone Layer Mesosphere Thermosphere –Ionosphere 4. Layers in the atmosphere are defined by temperature profiles

14. 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 4. Layers in the atmosphere are defined by temperature profiles

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 (O 3 ) is effective at absorbing solar ultraviolet radiation 4. Layers in the atmosphere are defined by temperature profiles

16. Mesosphere 50 – 80 km altitude Temperature decreases with altitude 0 C at base, -95 C at top Top is coldest region of atmosphere 4. Layers in the atmosphere are defined by temperature profiles

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 4. Layers in the atmosphere are defined by temperature profiles

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 4. Layers in the atmosphere are defined by temperature profiles

19. 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/cm 2 ) Pressure of ten meters of water Approximately one bar or 100 kPa Weather reports use millibars (mb) One mb = pressure of one cm water 5. How pressure varies in the atmosphere

20. 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 5. How pressure varies in the atmosphere

21. Pressure and Altitude 5. How pressure varies in the atmosphere

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 5. How pressure varies in the atmosphere

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 5. How pressure varies in the atmosphere

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 5. How pressure varies in the atmosphere

25. Atmospheric Measurements Temperature Pressure Humidity Wind Velocity and Direction 6. Principal weather instruments

26. Weather Instruments Temperature: Thermometer Pressure:Barometer Humidity:Hygrometer Wind Velocity and Direction: Anemometer and Wind Vane 6. Principal weather instruments

27. Thermometers Fluid –Mercury –Alcohol –Use expansion of fluid Bimetallic –Differential expansion of different metals Electronic –Electrical resistance change with temperature 6. Principal weather instruments

28. 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 6. Principal weather instruments

29. 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 6. Principal weather instruments

30. Sounding Balloons carry radiosondes –Thermometer –Barometer –Hygrometer –Transmitter Typically reach 30 km before balloon breaks 6. Principal weather instruments

31. Radar Detect precipitation types and amounts Doppler radar measures velocity of winds 6. Principal weather instruments

32. Satellite Studies Visual imagery Infrared imagery Laser spectroscopy 6. Principal weather instruments

33. Earth’s Radiation Budget What comes in must go out Direct Reflectance (Short Wave) –31% Infrared Re-emission (Long Wave) –69% 7. Earth’s radiation budget

34. How Heat Moves Radiation Conduction Convection 7. Earth’s radiation budget

35. 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% 7. Earth’s radiation budget

36. Global Albedo 7. Earth’s radiation budget