1. Part 1. Energy and Mass Chapter 1. Composition and Structure of the Atmosphere

2. Meteorology The study of the atmosphere and the processes that cause “weather” Climatology Examines weather elements over long time periods

3. Introduction The Atmosphere A mixture of gas molecules, suspended particles, and falling precipitation The atmosphere strongly affects our day-to- day lives

4. The Thickness of the Atmosphere Density decreases rapidly with height The top of the atmosphere is undefined Majority of mass is compressed near the surface

5. Gases and particles are exchanged between the surface and atmosphere A gas molecule that is input slowly into the atmosphere has a long average residence time. A gas molecule that is input rapidly into the atmosphere has a short average residence time. Average residence time of CO 2 is about 100 years.

6. Evolution of the Atmosphere Early atmosphere = hydrogen (H 2 ) and helium (He) -- 4 billion years ago Secondary atmosphere formed from volcanic outgassing (produced CO 2 rich atmosphere) -- 4 to 3 billion years ago CO 2 replaced by O 2 through photosynthesis (by life!) and dissolution in water -- by 3.4 billion years ago; significant free O 2 by 2.5 billion years ago N 2 (inert) slowly grew to present day levels

7. Composition of the Atmosphere

8. Variable Gases

9. Water Vapor Most abundant variable gas Added/ removed to air through the hydrologic cycle Concentrations = nearly 0% to nearly 4% (by volume) Important to energy balance and many atmospheric processes (it is a greenhouse gas)

10. Water vapor image showing broader distribution of moisture than the image of actual clouds (below) Water vapor image Cloud image Dry air Moist air

11. Carbon Dioxide A trace gas 0.038% of atmosphere’s mass Important to Earth’s energy balance (it is a greenhouse gas) Added through biologic respiration, volcanic activity, decay, and natural and human-related combustion Removed through photosynthesis Increasing at a rate of 1.8 ppm/year

12. Temporal increases due to human activities Seasonal variations related to biological activity 2006 value: about 380 ppm

13. Methane A variable gas in small but recently increasing concentrations Increases from burning of fossil fuels, livestock digestion, and agriculture cultivation (esp. rice) Effective absorber of terrestrial radiation (it is a greenhouse gas) Plays a role in near-surface warming

14. The annual increases in atmospheric methane

15. Aerosols (particulates) Any solid and/or liquid particle, other than water Both natural (sea spray, dust, combustion) and human (combustion) sources Long residence times for some types Acts as condensation nuclei Will cool atmosphere if emitted in large amounts (such as volcanic eruptions)

16. Vertical Structure of the Atmosphere Density Mass (kg) per unit volume (m 3 ) Sea level average = 1.2 kg/m 3 Near surface air is more dense Compressibility of air Mean free path (of an air molecule) –At surface = 0.0001 mm –At 150 km = 10 m Elevation in the atmosphere Higher density Lower density

17. Thermal Layers of the Atmosphere Four distinct atmospheric layers Troposphere Stratosphere Mesosphere Thermosphere Each has particular temperature characteristics with height.

18. Troposphere Lowest layer Steady temperature decrease with height -6.5 o C/km (-3.6 o F/1000ft) Virtually all weather processes Contains 80% of atmospheric mass Tropopause = top of troposphere

19. Violent updrafts may penetrate cloud tops into the stratosphere. The flattened top of this cumulonimbus cloud is in the stratosphere.

20. Stratosphere Little actual “weather” Temperature inversion Caused by absorption of UV radiation by O 3 (ozone) in the ozone layer Stratopause = top of stratosphere

21. Ozone Tri-atomic form of oxygen Absorbs ultraviolet radiation Chlorofluorocarbons (CFCs) destroy ozone Destruction peaks over southern hemisphere Antarctic circumpolar vortex limits latitudinal mixing Leads to an O 3 “hole”

22. The reduction of ozone over Antarctica over time. Area in red indicates the “ozone hole.”

23. Mesosphere Decreasing temperatures with height Coldest layer Thermosphere Slowly merges into space Increasing temperatures with height “Temperature” = molecular kinetic energy Combined Mesosphere and Thermosphere = 0.1% of total mass of atmosphere

25. Ionosphere A layer of electrically charged particles (ions) In the meso- and thermosphere D-, E-, and F-layers with increasing height Interactions with subatomic solar particles cause The aurora borealis (northern lights) The aurora australis (southern lights)

26. The ionosphere reflects radio waves, allowing radio transmissions over long distances around the Earth.

27. Temperature Energy of the atmosphere, measured in degrees (Fahrenheit, Celsius or Kelvin) Humidity Water content of the atmosphere, often expressed as relative humidity Pressure Force of the atmosphere, measured in millibars (mb) or kilopascals (kPa) Weather Measurements and Units

29. A Brief History of Meteorology Galileo Prototype thermometer in 1593 Fahrenheit (1714) and Celsius (1736) temperature scales Torricelli Barometer (1643) Instruments to measure water vapor introduced in late 1700s