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Fig. 2-CO, p. 26

Fig. 2-CO, p. 26. ENERGY: Warming the Earth & Atmosphere. Energy – The capacity to do work on matter. Gravitational Potential Energy – an object has the potential to do work (stored energy) PE= mgh Kinetic Energy – energy possessed by moving matter. KE ½ m v 2

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Fig. 2-CO, p. 26

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  1. Fig. 2-CO, p. 26

  2. ENERGY: Warming the Earth & Atmosphere • Energy– The capacity to do work on matter. • Gravitational Potential Energy – an object has the potential to do work (stored energy) PE= mgh • Kinetic Energy – energy possessed by moving matter. KE ½ m v2 • Temperature – measure of the average • Speed of atoms and molecule

  3. Fig. 2-1, p. 29

  4. ENERGY: Warming the Earth & Atmosphere • KE = ½ mv2 = 5/2 kT (diatomic gases) • so KE ~ v2 ~ T • Heat – is the energy that is transferred from one object to another as a result of a temperature difference between them. The heat transferred is added to the stored energy of the object. • Heat is transferred by the processes of Conduction, Convection, and Radiation.

  5. ENERGY: Warming the Earth & Atmosphere • Temperature scales • Absolute – Kelvin lowest temperature = 0 K • and 273.15 K = boiling point of H2O • Relative -- Celsius 0oC = freezing point of H2O • and 100 C = boiling point of H2 O • -- Fahrenheit 32oF = freezing pt of H2O • 212oF = boiling pt. of H2O

  6. Fig. 2-2, p. 30

  7. Potential Energy • The potential energy (stored energy) of an object is measured by the specific heat and the latent heat. • The specific heat is the energy added when a 1 C or K temperature change occurs for unit mass. • The latent energy value of potential energy is released when matter changes state from a gas liquid or liquid  solid.

  8. Table 2-1, p. 30

  9. Latent Heat Processes • Gaining Latent Heat (Environment cools) • Melting Solid  Liquid • Evaporation Liquid  Gas (or vapor) • Sublimation Solid  Gas (or vapor) • Releasing Latent Heat (Environment heats) • Freezing Liquid  Solid • Condensation Gas (or vapor)  Liquid • Deposition Gas (or vapor)  Solid

  10. Fig. 2-3, p. 31

  11. Fig. 2-4, p. 31

  12. Fig. 1, p. 32

  13. Heating Processes of the Atmosphere • Consider how the atmosphere is heated by Conduction, Convection and Radiation • CONDUCTION – Heating by transfer from molecule to molecule within the substance • Air is a poor conductor. • Liquids are better conductors. • Solids are the best conductors.

  14. Fig. 2-5, p. 33

  15. Table 2-2, p. 33

  16. Heat Convection • Convection – heat transfer by mass movement of a fluid. • Air Thermal is the vertical movement of air molecules as a result of a density difference. • ConvectiveCirculation movement of warm air upwards where is cooled and then falling air because it’s heavier density.

  17. Fig. 2-6, p. 34

  18. Heat Convection • The wind carries the air mass horizontally if there convection by moving over a cooler or warmer surface then it is called Advection. • When the wind causes air to rise over a topographical obstacle it is called orographic uplift. On the windward side of the obstacle there will be cooling and on the lee side there will be warming.

  19. Fig. 2, p. 34

  20. Radiation Heating • Radiation – is the heating by absorption of electromagnetic waves into an object. • Since every object has a temperature that body emits electromagnetic radiation. • The amount of heating of an object by radiation is the difference between the amount of heat absorbed by radiation and the heat loss by emission.

  21. ELECTROMAGNETIC WAVES • Electromagnetic waves travel at the speed of light in either free space or in a medium. The speed of light in free space is the largest and is c= 2.997 x 108 m/s this is approximated as 3 x 108 m/s. • The energy of a photon of a wave is given by E = h f where f is the frequency of a wave. Often we refer to the wavelength. • f = c/λ then Energy E = hc/λ so E ~ 1/λ

  22. Fig. 2-7, p. 35

  23. Radiation Heating • The amount of energy emitted per second by a body of unit area and temperature T is E = σ T4 this is the Stefan-Boltzmann Law. T is in K and σ = 5.67 x 10-8 w/m-2 K-4 • The temperature of the surface of the sun is 5800 K (5628 oC = 10,500 oF) and the earth is 288 K (15oC = 59oF) • The maximum radiated wavelength emitted is by Wien’s Law λ=2897(mμ)/T(K)

  24. Fig. 2-8, p. 37

  25. Solar and Earth Radiation Maximum Wavelength • Since the temperature of the sun is 5800K one can find the maximum wavelength emitted by using Wien’s Law. • λ = 2897 μm K/ 5800 K = 0.50 μm. • For the earth which has a temperature of 288K, the maximum wavelength emitted is • λ= 2897 μm K/ 288 K = 10 μm.

  26. Fig. 2-9, p. 37

  27. Solar and Earth Radiation Characteristics • Most of the radiation emitted from the sun is 0.2 to 2.0 μm. Referred to as shortwave radiation (UV, Visible, and near IR). • Most of Earth’s radiation is between 4 and 20 μm which is longwave radiation (IR). • The temp ratio of sun to earth is 20x, so radiation ratio of sun to earth, given by Stefan-Boltzmann’s Law is 160,000 x

  28. Solar Flux, Intensity and Solar Constant • Solar Flux is the amount of radiation emitted by the sun’s surface area per unit time and is calculated as the blackbody radiation. It is a constant throughout space. There are changes in flux due to solar flares and sunspot activity. • The Intensity (I) is the amount of Energy per unit surface area. It is the flux per unit area. I decreases as one increases the distance from the sun. I ~ 1/R2.

  29. Fig. 3, p. 38

  30. Solar Flux, Intensity and Solar Constant • The solar intensity at the top of the earth’s atmosphere is called the average solar constant and is 1367 W/m2. So on a 1 m2 surface perpendicular to the sun’s energy there is 1367 W. That intensity is reduced because of the opacity of the atmosphere and the presence of aerosols to1000 W this is called the insolation. In this county taking into consideration clouds it is 300 W. Averaged annually per day is 156 W.

  31. HUMAN UV PROTECTION • The NWS makes a daily UV prediction for UV for selected cities throughout the US. • These predictions allow one to use UV blockers (sun screen) to prevent UV reaching the skin. • Sun screen uses a solar protection factor SPF. 15 SPF is equivalent to the same UV exposure in 15 minutes compared to a 1 minute exposure without using sun screen.

  32. Fig. 4, p. 39

  33. Equilibrium -- Balancing Absorption and Emission • Any object radiates energy. So the earth absorbs solar energy and radiates some of its internal energy according to its temperature. Thus equilibrium of a body is established when Eab = Eemit • Since the rate of emission is not as great as the amount receives from the sun, the temperature of the earth can increase or decrease it’s temperature.

  34. Fig. 2-10, p. 40

  35. Equilibrium -- Balancing Absorption and Emission • An object that can absorb all the energy it receives is a perfect absorber. This the characteristic of a blackbody. These bodies not only absorb all that they receive but emit all the energy possible by the Stefan-Boltzmann Law. This is known as Kirchhoff’s radiation Law. Both the sun and the earth can be considered blackbodies.

  36. Equilibrium -- Balancing Absorption and Emission • Snow is a good absorber and good emitter at IR frequencies. While that does not happen at visible wavelengths. This is also a part of Kirchhoff’s Law. • Those objects which have different absorption characteristics for different wavelengths are known as selective filters. Most of the gases in our atmosphere are selective filters and also emit radiation.

  37. Fig. 2-11a, p. 41

  38. Fig. 2-11b, p. 41

  39. Fig. 2-11c, p. 41

  40. Equilibrium -- Balancing Absorption and Emission • The selective filters also give rise to the greenhouse effect. In this case atmospheric gases allow visible light to pass through while absorbing the infrared wavelengths. Since these gases also radiate energy this will cause a buildup of the earth’s temperature. This process also occurs for glass and is used to keep green houses warm all year.

  41. Fig. 2-12, p. 42

  42. Solar Constant and Insolation • The average incoming solar energy at the top of the atmosphere is 1367 W/m2 this is the Solar Constant. The atmosphere absorbs some of the energy and clouds reflect some energy so that only 51% of the radiation is directly absorbed by the surface, The average insolation value is 697 W/m2 and varies locally depending on clouds, aerosols and the sun’s angle.

  43. Fig. 2-13, p. 44

  44. Table 2-3, p. 44

  45. Fig. 2-14, p. 45

  46. Fig. 2-15, p. 45

  47. Fig. 5, p. 46

  48. Fig. 6, p. 46

  49. Fig. 7, p. 46

  50. Fig. 2-16, p. 47

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