Warming the Earth and the Atmosphere

1. Warming the Earth and the Atmosphere • Temperature and heat transfer • Balancing act - absorption, emission and equilibrium • Incoming solar energy

2. Temperature and Heat Transfer • Temperature and Heat are NOT the same thing! • Temperature is the average kinetic energy of a group of particles (atoms or molecules). • Heat is a quantity of energy. • “Heating” is sometimes used to denote a change in temperature – NOT IN GES 241! Adding or subtracting a quantity of heat energy may OR MAY NOT result in a temperature change.

3. Temperature Scales • kinetic energy, temperature and heat • Kelvin scale • Celsius scale • Fahrenheit scale • temperature conversions • Every temperature scale has two physically-meaningfulcharacteristics: a zero point and a degree interval.

4. Fig. 2-2, p. 27

5. Temperature as Average Kinetic Energy • Atoms/molecules have mass and move at some speed, thus have kinetic energy: KE = ½ mv2 • Too many particles to keep track of all those individual kinetic energies (one for each particle) • Temperature is the average kinetic energy of all the particles in a substance

6. Ideal Gas Law

7. Ideal Gas Law p = ρR T p: gas pressure T: gas temperature ρ: gas density R is a constant for any given mixture of gases but changes from gas to gas. For dry air, R = 287 J kg-1 K-1

8. Phases of Matter

9. Phases of Matter Phases and Pressure • Phase of a substance depends on both temperature and pressure • Often more than one phase is present

10. Phase Changes • Ionization: Stripping of electrons, changing atoms into plasma • Dissociation: Breaking of molecules into atoms • Evaporation: Breaking of flexible chemical bonds, changing liquid into solid • Melting: Breaking of rigid chemical bonds, changing solid into liquid

11. Latent Heat - The Hidden Warmth • phase changes and energy exchanges • sensible heat • Latent heat explains why your skin feels cold whenyou step out of a warm shower, and why perspirationis an effective way to cool your body.

12. Stepped Art Fig. 2-3, p. 28

13. Conduction • conduction and heat transfer • good conductors and poor conductors • Why are feathers (down) used in winter parkas?

14. Convection • convection and heat transfer • thermals • Soaring birds, like hawks and falcons, are highlyskilled at finding thermals.

15. Radiation • radiation and energy transfer • electromagnetic waves • Wein’s law • Stefan-Boltzmann law • Selective absorption of radiation: Greenhous Gases

16. What is light? • Light can act either like a wave or like a particle • Particles of light are called photons

17. Waves • A wave is a pattern of motion that can carry energy without carrying matter along with it

18. Properties of Waves • Wavelength (λ) is the distance between two wave peaks • Frequency (ν) is the number of times per second that a wave vibrates up and down • Wave Speed (c) is the distance one point on the wave travels in one second c = λν

19. Light: Electromagnetic Waves • A light wave is a vibration of electric and magnetic fields • Light interacts with charged particles through these electric and magnetic fields

20. Wavelength and Frequency wavelength x frequency = speed of light = constant

21. Fig. 2-7, p. 32

22. Radiation • electromagnetic spectrum • ultraviolet radiation • visible radiation • infrared radiation • Moderate amounts of ultraviolet radiation gives you a healthy-looking tan; excessive amounts give you skin cancer.

23. The Concept of Flux Flux: the quantity passing through a unit area in a unit time Example: Energy Flux in SI units. Energy Flux = “the number of Joules of energy passing through 1 square meter in one second” Units of Energy Flux: Js-1m-2 = Wm-2 (Chalkboard Example)

24. Fig. 2-8, p. 34

25. Stefan-Boltzmann Law “The hotter the object, the more it radiates.” F = σT4 F: energy flux from body at temperature T (units: Wm-2) T: temperature of body σ: Stefan-Boltzmann constant, σ=5.67x10-8 Wm-2K-4

26. Stefan-Boltzmann Law • Blackbody flux is the total area under the curve. • Fourth power means hot objects are radiating MUCH more than cool ones • Example: 2 objects, one at 300 K and one at 600 K. One object is twice as hot, but it radiates 16 times the energy from each square meter of its surface than the cooler one.

27. Fig. 2-9, p. 34

28. Wien’s Law “The hotter the object, the shorter wavelength light it emits.” λmax = C / T λmax: Wavelength of maximum blackbody emission (in microns/micrometers, μm) C: constant, C = 2898 μm K T: body temperature in K

29. Wien’s Law Example 1: Earth at 288 K λmax = 2898 μm K / 288 K = 10 μm 10 microns is IR radiation. Earth radiates mostly in the infrared. Example 2: The Sun at 5778 K λmax = 2898 μm K / 5778 K = 0.501 μm = 501 nm 501 nm is visible (green) radiation. The Sun radiates mostly in the visible (green).

30. Balancing Act - Absorption, Emission, and Equilibrium

31. Selective Absorbers and the Atmospheric Greenhouse Effect • blackbody radiation • selective absorbers • atmospheric greenhouse effect • The best greenhouse gas is water vapor.

32. Particles of Light • Particles of light are called photons • Each photon has a wavelength and a frequency • The energy of a photon depends on its frequency

33. Wavelength, Frequency, and Energy lν = c λ = wavelength ν= frequency c = 3.00 x 108 ms-1 “speed of light” E = h ν photon energy h = 6.626 x 10-34 J s

34. Atomic Analogy: Child’s Playslide (Chalkboard)

35. Energy Level Transitions • The only allowed changes in energy are those corresponding to a transition between energy levels Not Allowed Allowed (Hydrogen Atom)

36. Chemical Fingerprints • We can plot those energy transitions as frequencies (because of E=hν ) and therefore as wavelengths (because of c=λν) • Each type of atom has a unique spectral fingerprint

37. Energy Levels of Molecules • Molecules have additional energy levels because they can vibrate and rotate

38. Energy Levels of Molecules • The large numbers of vibrational and rotational energy levels can make the spectra of molecules very complicated • Many of these molecular transitions are in the infrared part of the spectrum

39. So how does the greenhouse effect work then… Atmosphere contains gases that selectively absorb IR radiation, but transmit visible light (“greenhouse gases”) Visible light (from the 5778 K Sun) travels through the atmosphere and is absorbed by the surface. The surface (≈ 300 K) re-radiates that energy upward as IR light. The IR energy gets absorbed by atmospheric GHGs. The atmosphere radiates some upward to space, but also back downward to the surface. This energy raises the temperature of the ground.

40. The simplest greenhouse effect calculation you can do… (Chalkboard)

41. The Global Energy Budget Just like a bank budget: Bank: In = Out + Savings Earth Energy: In = Out + Energy Storage Energy can be stored in many ways, including temperature can change. Working definition of weather: “Weather is the dynamical way in which the atmosphere maintains the long-term global energy balance.”

42. The Bathtub Analogy for Energy Balance (Chalkboard)

43. Incoming Solar Energy

44. The Earth’s Annual Energy Balance • What happens to the solar energy that reaches the top of the earth’s atmosphere? • What happens to the solar energy that is absorbed by the earth’s surface and by the atmosphere?

45. Scattered and Reflected Light • scattering • reflection • albedo • Scattering is responsible for the blue sky color.

46. Fig. 2-15, p. 41

47. Fig. 2-16, p. 42

48. FIGURE 2.16 The earth-atmosphere energy balance. Numbers represent approximations based on surface observations and satellite data. While the actual value of each process may vary by several percent, it is the relative size of the numbers that is important. Stepped Art Fig. 2-16, p. 42

49. Why the Earth has Seasons • earth-sun distance • tilt of the earth’s axis • Earth-sun distance has little effect on atmospheric temperature.

50. Seasons in the Northern Hemisphere • insolation • summer solstice • spring and autumn equinox